FreeBSD Manual Pages
IPFW(8) FreeBSD System Manager's Manual IPFW(8) NAME ipfw, dnctl -- User interface for firewall, traffic shaper, packet sched- uler, in-kernel NAT. SYNOPSIS FIREWALL CONFIGURATION ipfw [-cq] add rule ipfw [-acdefnNStT] [set N] {list | show} [rule | first-last ...] ipfw [-f | -q] [set N] flush ipfw [-q] [set N] {delete | zero | resetlog} [number ...] ipfw set [disable number ...] [enable number ...] ipfw set move [rule] number to number ipfw set swap number number ipfw set show SYSCTL SHORTCUTS ipfw enable {firewall | altq | one_pass | debug | verbose | dyn_keepalive} ipfw disable {firewall | altq | one_pass | debug | verbose | dyn_keepalive} LOOKUP TABLES ipfw [set N] table name create create-options ipfw [set N] table {name | all} destroy ipfw [set N] table name modify modify-options ipfw [set N] table name swap name ipfw [set N] table name add table-key [value] ipfw [set N] table name add [table-key value ...] ipfw [set N] table name atomic add [table-key value ...] ipfw [set N] table name delete [table-key ...] ipfw [set N] table name lookup addr ipfw [set N] table name lock ipfw [set N] table name unlock ipfw [set N] table {name | all} list ipfw [set N] table {name | all} info ipfw [set N] table {name | all} detail ipfw [set N] table {name | all} flush DUMMYNET CONFIGURATION (TRAFFIC SHAPER AND PACKET SCHEDULER) dnctl {pipe | queue | sched} number config config-options dnctl [-s [field]] {pipe | queue | sched} {delete | list | show} [number ...] IN-KERNEL NAT ipfw [-q] nat number config config-options ipfw nat number show {config | log} STATEFUL IPv6/IPv4 NETWORK ADDRESS AND PROTOCOL TRANSLATION ipfw [set N] nat64lsn name create create-options ipfw [set N] nat64lsn name config config-options ipfw [set N] nat64lsn {name | all} {list | show} [states] ipfw [set N] nat64lsn {name | all} destroy ipfw [set N] nat64lsn name stats [reset] STATELESS IPv6/IPv4 NETWORK ADDRESS AND PROTOCOL TRANSLATION ipfw [set N] nat64stl name create create-options ipfw [set N] nat64stl name config config-options ipfw [set N] nat64stl {name | all} {list | show} ipfw [set N] nat64stl {name | all} destroy ipfw [set N] nat64stl name stats [reset] XLAT464 CLAT IPv6/IPv4 NETWORK ADDRESS AND PROTOCOL TRANSLATION ipfw [set N] nat64clat name create create-options ipfw [set N] nat64clat name config config-options ipfw [set N] nat64clat {name | all} {list | show} ipfw [set N] nat64clat {name | all} destroy ipfw [set N] nat64clat name stats [reset] IPv6-to-IPv6 NETWORK PREFIX TRANSLATION ipfw [set N] nptv6 name create create-options ipfw [set N] nptv6 {name | all} {list | show} ipfw [set N] nptv6 {name | all} destroy ipfw [set N] nptv6 name stats [reset] INTERNAL DIAGNOSTICS ipfw internal iflist ipfw internal talist ipfw internal vlist LIST OF RULES AND PREPROCESSING ipfw [-cfnNqS] [-p preproc [preproc-flags]] pathname DESCRIPTION The ipfw utility is the user interface for controlling the ipfw(4) fire- wall, the dummynet(4) traffic shaper/packet scheduler, and the in-kernel NAT services. A firewall configuration, or ruleset, is made of a list of rules numbered from 1 to 65535. Packets are passed to the firewall from a number of different places in the protocol stack (depending on the source and des- tination of the packet, it is possible for the firewall to be invoked multiple times on the same packet). The packet passed to the firewall is compared against each of the rules in the ruleset, in rule-number order (multiple rules with the same number are permitted, in which case they are processed in order of insertion). When a match is found, the action corresponding to the matching rule is performed. Depending on the action and certain system settings, packets can be rein- jected into the firewall at some rule after the matching one for further processing. A ruleset always includes a default rule (numbered 65535) which cannot be modified or deleted, and matches all packets. The action associated with the default rule can be either deny or allow depending on how the kernel is configured. If the ruleset includes one or more rules with the keep-state, record-state, limit or set-limit option, the firewall will have a stateful behaviour, i.e., upon a match it will create dynamic rules, i.e., rules that match packets with the same 5-tuple (protocol, source and destination addresses and ports) as the packet which caused their creation. Dynamic rules, which have a limited lifetime, are checked at the first occurrence of a check-state, keep-state or limit rule, and are typically used to open the firewall on-demand to legitimate traffic only. Please note, that keep-state and limit imply implicit check-state for all packets (not only these matched by the rule) but record-state and set-limit have no implicit check-state. See the STATEFUL FIREWALL and EXAMPLES Sections below for more information on the stateful behaviour of ipfw. All rules (including dynamic ones) have a few associated counters: a packet count, a byte count, a log count and a timestamp indicating the time of the last match. Counters can be displayed or reset with ipfw commands. Each rule belongs to one of 32 different sets , and there are ipfw com- mands to atomically manipulate sets, such as enable, disable, swap sets, move all rules in a set to another one, delete all rules in a set. These can be useful to install temporary configurations, or to test them. See Section SETS OF RULES for more information on sets. Rules can be added with the add command; deleted individually or in groups with the delete command, and globally (except those in set 31) with the flush command; displayed, optionally with the content of the counters, using the show and list commands. Finally, counters can be re- set with the zero and resetlog commands. COMMAND OPTIONS The following general options are available when invoking ipfw: -a Show counter values when listing rules. The show command implies this option. -b Only show the action and the comment, not the body of a rule. Implies -c. -c When entering or showing rules, print them in compact form, i.e., omitting the "ip from any to any" string when this does not carry any additional information. -d When listing, show dynamic rules in addition to static ones. -D When listing, show only dynamic states. When deleting, delete only dynamic states. -f Run without prompting for confirmation for commands that can cause problems if misused, i.e., flush. If there is no tty asso- ciated with the process, this is implied. The delete command with this flag ignores possible errors, i.e., nonexistent rule number. And for batched commands execution continues with the next command. -i When listing a table (see the LOOKUP TABLES section below for more information on lookup tables), format values as IP ad- dresses. By default, values are shown as integers. -n Only check syntax of the command strings, without actually pass- ing them to the kernel. -N Try to resolve addresses and service names in output. -q Be quiet when executing the add, nat, zero, resetlog or flush commands; (implies -f). This is useful when updating rulesets by executing multiple ipfw commands in a script (e.g., `sh /etc/rc.firewall'), or by processing a file with many ipfw rules across a remote login session. It also stops a table add or delete from failing if the entry already exists or is not present. The reason why this option may be important is that for some of these actions, ipfw may print a message; if the action results in blocking the traffic to the remote client, the remote login ses- sion will be closed and the rest of the ruleset will not be pro- cessed. Access to the console would then be required to recover. -S When listing rules, show the set each rule belongs to. If this flag is not specified, disabled rules will not be listed. -s [field] When listing pipes, sort according to one of the four counters (total or current packets or bytes). -t When listing, show last match timestamp converted with ctime(). -T When listing, show last match timestamp as seconds from the epoch. This form can be more convenient for postprocessing by scripts. LIST OF RULES AND PREPROCESSING To ease configuration, rules can be put into a file which is processed using ipfw as shown in the last synopsis line. An absolute pathname must be used. The file will be read line by line and applied as arguments to the ipfw utility. Optionally, a preprocessor can be specified using -p preproc where pathname is to be piped through. Useful preprocessors include cpp(1) and m4(1). If preproc does not start with a slash (`/') as its first charac- ter, the usual PATH name search is performed. Care should be taken with this in environments where not all file systems are mounted (yet) by the time ipfw is being run (e.g. when they are mounted over NFS). Once -p has been specified, any additional arguments are passed on to the pre- processor for interpretation. This allows for flexible configuration files (like conditionalizing them on the local hostname) and the use of macros to centralize frequently required arguments like IP addresses. TRAFFIC SHAPER CONFIGURATION The dnctl pipe, queue and sched commands are used to configure the traf- fic shaper and packet scheduler. See the TRAFFIC SHAPER (DUMMYNET) CONFIGURATION Section below for details. If the world and the kernel get out of sync the ipfw ABI may break, pre- venting you from being able to add any rules. This can adversely affect the booting process. You can use ipfw disable firewall to temporarily disable the firewall to regain access to the network, allowing you to fix the problem. PACKET FLOW A packet is checked against the active ruleset in multiple places in the protocol stack, under control of several sysctl variables. These places and variables are shown below, and it is important to have this picture in mind in order to design a correct ruleset. ^ to upper layers V | | +----------->-----------+ ^ V [ip(6)_input] [ip(6)_output] net.inet(6).ip(6).fw.enable=1 | | ^ V [ether_demux] [ether_output_frame] net.link.ether.ipfw=1 | | +-->--[bdg_forward]-->--+ net.link.bridge.ipfw=1 ^ V | to devices | The number of times the same packet goes through the firewall can vary between 0 and 4 depending on packet source and destination, and system configuration. Note that as packets flow through the stack, headers can be stripped or added to it, and so they may or may not be available for inspection. E.g., incoming packets will include the MAC header when ipfw is invoked from ether_demux(), but the same packets will have the MAC header stripped off when ipfw is invoked from ip_input() or ip6_input(). Also note that each packet is always checked against the complete rule- set, irrespective of the place where the check occurs, or the source of the packet. If a rule contains some match patterns or actions which are not valid for the place of invocation (e.g. trying to match a MAC header within ip_input or ip6_input ), the match pattern will not match, but a not operator in front of such patterns will cause the pattern to always match on those packets. It is thus the responsibility of the programmer, if necessary, to write a suitable ruleset to differentiate among the pos- sible places. skipto rules can be useful here, as an example: # packets from ether_demux or bdg_forward ipfw add 10 skipto 1000 all from any to any layer2 in # packets from ip_input ipfw add 10 skipto 2000 all from any to any not layer2 in # packets from ip_output ipfw add 10 skipto 3000 all from any to any not layer2 out # packets from ether_output_frame ipfw add 10 skipto 4000 all from any to any layer2 out (yes, at the moment there is no way to differentiate between ether_demux and bdg_forward). Also note that only actions allow, deny, netgraph, ngtee and related to dummynet are processed for layer2 frames and all other actions act as if they were allow for such frames. Full set of actions is supported for IP packets without layer2 headers only. For example, divert action does not divert layer2 frames. SYNTAX In general, each keyword or argument must be provided as a separate com- mand line argument, with no leading or trailing spaces. Keywords are case-sensitive, whereas arguments may or may not be case-sensitive de- pending on their nature (e.g. uid's are, hostnames are not). Some arguments (e.g., port or address lists) are comma-separated lists of values. In this case, spaces after commas ',' are allowed to make the line more readable. You can also put the entire command (including flags) into a single argument. E.g., the following forms are equivalent: ipfw -q add deny src-ip 10.0.0.0/24,127.0.0.1/8 ipfw -q add deny src-ip 10.0.0.0/24, 127.0.0.1/8 ipfw "-q add deny src-ip 10.0.0.0/24, 127.0.0.1/8" RULE FORMAT The format of firewall rules is the following: [rule_number] [set set_number] [prob match_probability] action [log [logamount number]] [altq queue] [{tag | untag} number] body where the body of the rule specifies which information is used for fil- tering packets, among the following: Layer2 header fields When available IPv4 and IPv6 Protocol SCTP, TCP, UDP, ICMP, etc. Source and dest. addresses and ports Direction See Section PACKET FLOW Transmit and receive interface By name or address Misc. IP header fields Version, type of service, data- gram length, identification, fragmentation flags, Time To Live IP options IPv6 Extension headers Fragmentation, Hop-by-Hop op- tions, Routing Headers, Source routing rthdr0, Mobile IPv6 rthdr2, IPSec options. IPv6 Flow-ID Misc. TCP header fields TCP flags (SYN, FIN, ACK, RST, etc.), sequence number, acknowl- edgment number, window TCP options ICMP types for ICMP packets ICMP6 types for ICMP6 packets User/group ID When the packet can be associ- ated with a local socket. Divert status Whether a packet came from a di- vert socket (e.g., natd(8)). Fib annotation state Whether a packet has been tagged for using a specific FIB (rout- ing table) in future forwarding decisions. Note that some of the above information, e.g. source MAC or IP addresses and TCP/UDP ports, can be easily spoofed, so filtering on those fields alone might not guarantee the desired results. rule_number Each rule is associated with a rule_number in the range 1..65535, with the latter reserved for the default rule. Rules are checked sequentially by rule number. Multiple rules can have the same number, in which case they are checked (and listed) according to the order in which they have been added. If a rule is entered without specifying a number, the kernel will assign one in such a way that the rule becomes the last one before the default rule. Automatic rule numbers are assigned by incrementing the last non- default rule number by the value of the sysctl variable net.inet.ip.fw.autoinc_step which defaults to 100. If this is not possible (e.g. because we would go beyond the maximum allowed rule number), the number of the last non-default value is used instead. set set_number Each rule is associated with a set_number in the range 0..31. Sets can be individually disabled and enabled, so this parameter is of fundamental importance for atomic ruleset manipulation. It can be also used to simplify deletion of groups of rules. If a rule is entered without specifying a set number, set 0 will be used. Set 31 is special in that it cannot be disabled, and rules in set 31 are not deleted by the ipfw flush command (but you can delete them with the ipfw delete set 31 command). Set 31 is also used for the default rule. prob match_probability A match is only declared with the specified probability (floating point number between 0 and 1). This can be useful for a number of applications such as random packet drop or (in conjunction with dummynet) to simulate the effect of multiple paths leading to out-of-order packet delivery. Note: this condition is checked before any other condition, in- cluding ones such as keep-state or check-state which might have side effects. log [logamount number] Packets matching a rule with the log keyword will be made avail- able for logging in two ways: if the sysctl variable net.inet.ip.fw.verbose is set to 0 (default), one can use bpf(4) attached to the ipfw0 pseudo interface. This pseudo interface can be created manually after a system boot by using the follow- ing command: # ifconfig ipfw0 create Or, automatically at boot time by adding the following line to the rc.conf(5) file: firewall_logif="YES" There is zero overhead when no bpf(4) is attached to the pseudo interface. If net.inet.ip.fw.verbose is set to 1, packets will be logged to syslogd(8) with a LOG_SECURITY facility up to a maximum of logamount packets. If no logamount is specified, the limit is taken from the sysctl variable net.inet.ip.fw.verbose_limit. In both cases, a value of 0 means unlimited logging. Once the limit is reached, logging can be re-enabled by clearing the logging counter or the packet counter for that entry, see the resetlog command. Note: logging is done after all other packet matching conditions have been successfully verified, and before performing the final action (accept, deny, etc.) on the packet. tag number When a packet matches a rule with the tag keyword, the numeric tag for the given number in the range 1..65534 will be attached to the packet. The tag acts as an internal marker (it is not sent out over the wire) that can be used to identify these pack- ets later on. This can be used, for example, to provide trust between interfaces and to start doing policy-based filtering. A packet can have multiple tags at the same time. Tags are "sticky", meaning once a tag is applied to a packet by a matching rule it exists until explicit removal. Tags are kept with the packet everywhere within the kernel, but are lost when packet leaves the kernel, for example, on transmitting packet out to the network or sending packet to a divert(4) socket. To check for previously applied tags, use the tagged rule option. To delete previously applied tag, use the untag keyword. Note: since tags are kept with the packet everywhere in ker- nelspace, they can be set and unset anywhere in the kernel net- work subsystem (using the mbuf_tags(9) facility), not only by means of the ipfw(4) tag and untag keywords. For example, there can be a specialized netgraph(4) node doing traffic analyzing and tagging for later inspecting in firewall. untag number When a packet matches a rule with the untag keyword, the tag with the number number is searched among the tags attached to this packet and, if found, removed from it. Other tags bound to packet, if present, are left untouched. altq queue When a packet matches a rule with the altq keyword, the ALTQ identifier for the given queue (see altq(4)) will be attached. Note that this ALTQ tag is only meaningful for packets going "out" of IPFW, and not being rejected or going to divert sockets. Note that if there is insufficient memory at the time the packet is processed, it will not be tagged, so it is wise to make your ALTQ "default" queue policy account for this. If multiple altq rules match a single packet, only the first one adds the ALTQ classification tag. In doing so, traffic may be shaped by using count altq queue rules for classification early in the ruleset, then later applying the filtering decision. For example, check-state and keep-state rules may come later and provide the actual filtering decisions in addition to the fallback ALTQ tag. You must run pfctl(8) to set up the queues before IPFW will be able to look them up by name, and if the ALTQ disciplines are re- arranged, the rules in containing the queue identifiers in the kernel will likely have gone stale and need to be reloaded. Stale queue identifiers will probably result in misclassifica- tion. All system ALTQ processing can be turned on or off via ipfw enable altq and ipfw disable altq. The usage of net.inet.ip.fw.one_pass is irrelevant to ALTQ traffic shaping, as the actual rule action is followed always after adding an ALTQ tag. RULE ACTIONS A rule can be associated with one of the following actions, which will be executed when the packet matches the body of the rule. allow | accept | pass | permit Allow packets that match rule. The search terminates. check-state [:flowname | :any] Checks the packet against the dynamic ruleset. If a match is found, execute the action associated with the rule which gener- ated this dynamic rule, otherwise move to the next rule. Check-state rules do not have a body. If no check-state rule is found, the dynamic ruleset is checked at the first keep-state or limit rule. The :flowname is symbolic name assigned to dynamic rule by keep-state opcode. The special flowname :any can be used to ignore states flowname when matching. The :default keyword is special name used for compatibility with old rulesets. count Update counters for all packets that match rule. The search con- tinues with the next rule. deny | drop Discard packets that match this rule. The search terminates. divert port Divert packets that match this rule to the divert(4) socket bound to port port. The search terminates. fwd | forward ipaddr | tablearg[,port] Change the next-hop on matching packets to ipaddr, which can be an IP address or a host name. The next hop can also be supplied by the last table looked up for the packet by using the tablearg keyword instead of an explicit address. The search terminates if this rule matches. If ipaddr is a local address, then matching packets will be for- warded to port (or the port number in the packet if one is not specified in the rule) on the local machine. If ipaddr is not a local address, then the port number (if speci- fied) is ignored, and the packet will be forwarded to the remote address, using the route as found in the local routing table for that IP. A fwd rule will not match layer2 packets (those received on ether_input, ether_output, or bridged). The fwd action does not change the contents of the packet at all. In particular, the destination address remains unmodified, so packets forwarded to another system will usually be rejected by that system unless there is a matching rule on that system to capture them. For packets forwarded locally, the local address of the socket will be set to the original destination address of the packet. This makes the netstat(1) entry look rather weird but is intended for use with transparent proxy servers. nat nat_nr | global | tablearg Pass packet to a nat instance (for network address translation, address redirect, etc.): see the NETWORK ADDRESS TRANSLATION (NAT) Section for further information. nat64lsn name Pass packet to a stateful NAT64 instance (for IPv6/IPv4 network address and protocol translation): see the IPv6/IPv4 NETWORK ADDRESS AND PROTOCOL TRANSLATION Section for further information. nat64stl name Pass packet to a stateless NAT64 instance (for IPv6/IPv4 network address and protocol translation): see the IPv6/IPv4 NETWORK ADDRESS AND PROTOCOL TRANSLATION Section for further information. nat64clat name Pass packet to a CLAT NAT64 instance (for client-side IPv6/IPv4 network address and protocol translation): see the IPv6/IPv4 NETWORK ADDRESS AND PROTOCOL TRANSLATION Section for further in- formation. nptv6 name Pass packet to a NPTv6 instance (for IPv6-to-IPv6 network prefix translation): see the IPv6-to-IPv6 NETWORK PREFIX TRANSLATION (NPTv6) Section for further information. pipe pipe_nr Pass packet to a dummynet "pipe" (for bandwidth limitation, de- lay, etc.). See the TRAFFIC SHAPER (DUMMYNET) CONFIGURATION Sec- tion for further information. The search terminates; however, on exit from the pipe and if the sysctl(8) variable net.inet.ip.fw.one_pass is not set, the packet is passed again to the firewall code starting from the next rule. queue queue_nr Pass packet to a dummynet "queue" (for bandwidth limitation using WF2Q+). reject (Deprecated). Synonym for unreach host. reset Discard packets that match this rule, and if the packet is a TCP packet, try to send a TCP reset (RST) notice. The search termi- nates. reset6 Discard packets that match this rule, and if the packet is a TCP packet, try to send a TCP reset (RST) notice. The search termi- nates. skipto number | tablearg Skip all subsequent rules numbered less than number. The search continues with the first rule numbered number or higher. It is possible to use the tablearg keyword with a skipto for a computed skipto. Skipto may work either in O(log(N)) or in O(1) depending on amount of memory and/or sysctl variables. See the SYSCTL VARIABLES section for more details. call number | tablearg The current rule number is saved in the internal stack and rule- set processing continues with the first rule numbered number or higher. If later a rule with the return action is encountered, the processing returns to the first rule with number of this call rule plus one or higher (the same behaviour as with packets re- turning from divert(4) socket after a divert action). This could be used to make somewhat like an assembly language "subroutine" calls to rules with common checks for different interfaces, etc. Rule with any number could be called, not just forward jumps as with skipto. So, to prevent endless loops in case of mistakes, both call and return actions don't do any jumps and simply go to the next rule if memory cannot be allocated or stack over- flowed/underflowed. Internally stack for rule numbers is implemented using mbuf_tags(9) facility and currently has size of 16 entries. As mbuf tags are lost when packet leaves the kernel, divert should not be used in subroutines to avoid endless loops and other unde- sired effects. return Takes rule number saved to internal stack by the last call action and returns ruleset processing to the first rule with number greater than number of corresponding call rule. See description of the call action for more details. Note that return rules usually end a "subroutine" and thus are unconditional, but ipfw command-line utility currently requires every action except check-state to have body. While it is some- times useful to return only on some packets, usually you want to print just "return" for readability. A workaround for this is to use new syntax and -c switch: # Add a rule without actual body ipfw add 2999 return via any # List rules without "from any to any" part ipfw -c list This cosmetic annoyance may be fixed in future releases. tee port Send a copy of packets matching this rule to the divert(4) socket bound to port port. The search continues with the next rule. unreach code Discard packets that match this rule, and try to send an ICMP un- reachable notice with code code, where code is a number from 0 to 255, or one of these aliases: net, host, protocol, port, needfrag, srcfail, net-unknown, host-unknown, isolated, net-prohib, host-prohib, tosnet, toshost, filter-prohib, host-precedence or precedence-cutoff. The search terminates. unreach6 code Discard packets that match this rule, and try to send an ICMPv6 unreachable notice with code code, where code is a number from 0, 1, 3 or 4, or one of these aliases: no-route, admin-prohib, address or port. The search terminates. netgraph cookie Divert packet into netgraph with given cookie. The search termi- nates. If packet is later returned from netgraph it is either accepted or continues with the next rule, depending on net.inet.ip.fw.one_pass sysctl variable. ngtee cookie A copy of packet is diverted into netgraph, original packet con- tinues with the next rule. See ng_ipfw(4) for more information on netgraph and ngtee actions. setfib fibnum | tablearg The packet is tagged so as to use the FIB (routing table) fibnum in any subsequent forwarding decisions. In the current implemen- tation, this is limited to the values 0 through 15, see setfib(2). Processing continues at the next rule. It is possi- ble to use the tablearg keyword with setfib. If the tablearg value is not within the compiled range of fibs, the packet's fib is set to 0. setdscp DSCP | number | tablearg Set specified DiffServ codepoint for an IPv4/IPv6 packet. Pro- cessing continues at the next rule. Supported values are: cs0 (000000), cs1 (001000), cs2 (010000), cs3 (011000), cs4 (100000), cs5 (101000), cs6 (110000), cs7 (111000), af11 (001010), af12 (001100), af13 (001110), af21 (010010), af22 (010100), af23 (010110), af31 (011010), af32 (011100), af33 (011110), af41 (100010), af42 (100100), af43 (100110), va (101100), ef (101110), be (000000). Additionally, DSCP value can be specified by number (0..63). It is also possible to use the tablearg keyword with setdscp. If the tablearg value is not within the 0..63 range, lower 6 bits of supplied value are used. tcp-setmss mss Set the Maximum Segment Size (MSS) in the TCP segment to value mss. The kernel module ipfw_pmod should be loaded or kernel should have options IPFIREWALL_PMOD to be able use this action. This command does not change a packet if original MSS value is lower than specified value. Both TCP over IPv4 and over IPv6 are supported. Regardless of matched a packet or not by the tcp-setmss rule, the search continues with the next rule. reass Queue and reassemble IPv4 fragments. If the packet is not frag- mented, counters are updated and processing continues with the next rule. If the packet is the last logical fragment, the packet is reassembled and, if net.inet.ip.fw.one_pass is set to 0, processing continues with the next rule. Otherwise, the packet is allowed to pass and the search terminates. If the packet is a fragment in the middle of a logical group of frag- ments, it is consumed and processing stops immediately. Fragment handling can be tuned via net.inet.ip.maxfragpackets and net.inet.ip.maxfragsperpacket which limit, respectively, the max- imum number of processable fragments (default: 800) and the maxi- mum number of fragments per packet (default: 16). NOTA BENE: since fragments do not contain port numbers, they should be avoided with the reass rule. Alternatively, direction- based (like in / out ) and source-based (like via ) match pat- terns can be used to select fragments. Usually a simple rule like: # reassemble incoming fragments ipfw add reass all from any to any in is all you need at the beginning of your ruleset. abort Discard packets that match this rule, and if the packet is an SCTP packet, try to send an SCTP packet containing an ABORT chunk. The search terminates. abort6 Discard packets that match this rule, and if the packet is an SCTP packet, try to send an SCTP packet containing an ABORT chunk. The search terminates. RULE BODY The body of a rule contains zero or more patterns (such as specific source and destination addresses or ports, protocol options, incoming or outgoing interfaces, etc.) that the packet must match in order to be recognised. In general, the patterns are connected by (implicit) and op- erators -- i.e., all must match in order for the rule to match. Individ- ual patterns can be prefixed by the not operator to reverse the result of the match, as in ipfw add 100 allow ip from not 1.2.3.4 to any Additionally, sets of alternative match patterns (or-blocks) can be con- structed by putting the patterns in lists enclosed between parentheses ( ) or braces { }, and using the or operator as follows: ipfw add 100 allow ip from { x or not y or z } to any Only one level of parentheses is allowed. Beware that most shells have special meanings for parentheses or braces, so it is advisable to put a backslash \ in front of them to prevent such interpretations. The body of a rule must in general include a source and destination ad- dress specifier. The keyword any can be used in various places to spec- ify that the content of a required field is irrelevant. The rule body has the following format: [proto from src to dst] [options] The first part (proto from src to dst) is for backward compatibility with earlier versions of FreeBSD. In modern FreeBSD any match pattern (in- cluding MAC headers, IP protocols, addresses and ports) can be specified in the options section. Rule fields have the following meaning: proto: protocol | { protocol or ... } protocol: [not] protocol-name | protocol-number An IP protocol specified by number or name (for a complete list see /etc/protocols), or one of the following keywords: ip4 | ipv4 Matches IPv4 packets. ip6 | ipv6 Matches IPv6 packets. ip | all Matches any packet. The ipv6 in proto option will be treated as inner protocol. And, the ipv4 is not available in proto option. The { protocol or ... } format (an or-block) is provided for con- venience only but its use is deprecated. src and dst: {addr | { addr or ... }} [[not] ports] An address (or a list, see below) optionally followed by ports specifiers. The second format (or-block with multiple addresses) is provided for convenience only and its use is discouraged. addr: [not] {any | me | me6 | table(name[,value]) | addr-list | addr-set} any Matches any IP address. me Matches any IP address configured on an interface in the system. me6 Matches any IPv6 address configured on an interface in the system. The address list is evaluated at the time the packet is analysed. table(name[,value]) Matches any IPv4 or IPv6 address for which an entry ex- ists in the lookup table number. If an optional 32-bit unsigned value is also specified, an entry will match only if it has this value. See the LOOKUP TABLES section below for more information on lookup tables. addr-list: ip-addr[,addr-list] ip-addr: A host or subnet address specified in one of the following ways: numeric-ip | hostname Matches a single IPv4 address, specified as dotted-quad or a hostname. Hostnames are resolved at the time the rule is added to the firewall list. addr/masklen Matches all addresses with base addr (specified as an IP address, a network number, or a hostname) and mask width of masklen bits. As an example, 1.2.3.4/25 or 1.2.3.0/25 will match all IP numbers from 1.2.3.0 to 1.2.3.127 . addr:mask Matches all addresses with base addr (specified as an IP address, a network number, or a hostname) and the mask of mask, specified as a dotted quad. As an example, 1.2.3.4:255.0.255.0 or 1.0.3.0:255.0.255.0 will match 1.*.3.*. This form is advised only for non-contiguous masks. It is better to resort to the addr/masklen format for contiguous masks, which is more compact and less er- ror-prone. addr-set: addr[/masklen]{list} list: {num | num-num}[,list] Matches all addresses with base address addr (specified as an IP address, a network number, or a hostname) and whose last byte is in the list between braces { } . Note that there must be no spa- ces between braces and numbers (spaces after commas are allowed). Elements of the list can be specified as single entries or ranges. The masklen field is used to limit the size of the set of addresses, and can have any value between 24 and 32. If not specified, it will be assumed as 24. This format is particularly useful to handle sparse address sets within a single rule. Because the matching occurs using a bit- mask, it takes constant time and dramatically reduces the com- plexity of rulesets. As an example, an address specified as 1.2.3.4/24{128,35-55,89} or 1.2.3.0/24{128,35-55,89} will match the following IP ad- dresses: 1.2.3.128, 1.2.3.35 to 1.2.3.55, 1.2.3.89 . addr6-list: ip6-addr[,addr6-list] ip6-addr: A host or subnet specified one of the following ways: numeric-ip | hostname Matches a single IPv6 address as allowed by inet_pton(3) or a hostname. Hostnames are resolved at the time the rule is added to the firewall list. addr/masklen Matches all IPv6 addresses with base addr (specified as allowed by inet_pton(3) or a hostname) and mask width of masklen bits. addr/mask Matches all IPv6 addresses with base addr (specified as allowed by inet_pton(3) or a hostname) and the mask of mask, specified as allowed by inet_pton(3). As an exam- ple, fe::640:0:0/ffff::ffff:ffff:0:0 will match fe:*:*:*:0:640:*:*. This form is advised only for non- contiguous masks. It is better to resort to the addr/masklen format for contiguous masks, which is more compact and less error-prone. No support for sets of IPv6 addresses is provided because IPv6 addresses are typically random past the initial prefix. ports: {port | port-port}[,ports] For protocols which support port numbers (such as SCTP, TCP and UDP), optional ports may be specified as one or more ports or port ranges, separated by commas but no spaces, and an optional not operator. The `-' notation specifies a range of ports (in- cluding boundaries). Service names (from /etc/services) may be used instead of numeric port values. The length of the port list is limited to 30 ports or ranges, though one can specify larger ranges by using an or-block in the options section of the rule. A backslash (`\') can be used to escape the dash (`-') character in a service name (from a shell, the backslash must be typed twice to avoid the shell itself interpreting it as an escape character). ipfw add count tcp from any ftp\\-data-ftp to any Fragmented packets which have a non-zero offset (i.e., not the first fragment) will never match a rule which has one or more port specifications. See the frag option for details on matching fragmented packets. RULE OPTIONS (MATCH PATTERNS) Additional match patterns can be used within rules. Zero or more of these so-called options can be present in a rule, optionally prefixed by the not operand, and possibly grouped into or-blocks. The following match patterns can be used (listed in alphabetical order): // this is a comment. Inserts the specified text as a comment in the rule. Everything following // is considered as a comment and stored in the rule. You can have comment-only rules, which are listed as having a count action followed by the comment. bridged Alias for layer2. defer-immediate-action | defer-action A rule with this option will not perform normal action upon a match. This option is intended to be used with record-state or keep-state as the dynamic rule, created but ignored on match, will work as intended. Rules with both record-state and defer-immediate-action create a dynamic rule and continue with the next rule without actually performing the action part of this rule. When the rule is later activated via the state table, the action is performed as usual. diverted Matches only packets generated by a divert socket. diverted-loopback Matches only packets coming from a divert socket back into the IP stack input for delivery. diverted-output Matches only packets going from a divert socket back outward to the IP stack output for delivery. dst-ip ip-address Matches IPv4 packets whose destination IP is one of the ad- dress(es) specified as argument. {dst-ip6 | dst-ipv6} ip6-address Matches IPv6 packets whose destination IP is one of the ad- dress(es) specified as argument. dst-port ports Matches IP packets whose destination port is one of the port(s) specified as argument. established Matches TCP packets that have the RST or ACK bits set. ext6hdr header Matches IPv6 packets containing the extended header given by header. Supported headers are: Fragment, (frag), Hop-to-hop options (hopopt), any type of Rout- ing Header (route), Source routing Routing Header Type 0 (rthdr0), Mobile IPv6 Routing Header Type 2 (rthdr2), Destination options (dstopt), IPSec authentication headers (ah), and IPsec encapsulated security payload headers (esp). fib fibnum Matches a packet that has been tagged to use the given FIB (rout- ing table) number. flow table(name[,value]) Search for the flow entry in lookup table name. If not found, the match fails. Otherwise, the match succeeds and tablearg is set to the value extracted from the table. This option can be useful to quickly dispatch traffic based on certain packet fields. See the LOOKUP TABLES section below for more information on lookup tables. flow-id labels Matches IPv6 packets containing any of the flow labels given in labels. labels is a comma separated list of numeric flow labels. dst-mac table(name[,value]) Search for the destination MAC address entry in lookup table name. If not found, the match fails. Otherwise, the match suc- ceeds and tablearg is set to the value extracted from the table. src-mac table(name[,value]) Search for the source MAC address entry in lookup table name. If not found, the match fails. Otherwise, the match succeeds and tablearg is set to the value extracted from the table. frag spec Matches IPv4 packets whose ip_off field contains the comma sepa- rated list of IPv4 fragmentation options specified in spec. The recognized options are: df (don't fragment), mf (more fragments), rf (reserved fragment bit) offset (non-zero fragment offset). The absence of a particular options may be denoted with a `!'. Empty list of options defaults to matching on non-zero fragment offset. Such rule would match all not the first fragment data- grams, both IPv4 and IPv6. This is a backward compatibility with older rulesets. gid group Matches all TCP or UDP packets sent by or received for a group. A group may be specified by name or number. jail jail Matches all TCP or UDP packets sent by or received for the jail whose ID or name is jail. icmptypes types Matches ICMP packets whose ICMP type is in the list types. The list may be specified as any combination of individual types (nu- meric) separated by commas. Ranges are not allowed. The sup- ported ICMP types are: echo reply (0), destination unreachable (3), source quench (4), redirect (5), echo request (8), router advertisement (9), router solicitation (10), time-to-live exceeded (11), IP header bad (12), timestamp request (13), timestamp reply (14), information request (15), information reply (16), address mask request (17) and address mask reply (18). icmp6types types Matches ICMP6 packets whose ICMP6 type is in the list of types. The list may be specified as any combination of individual types (numeric) separated by commas. Ranges are not allowed. in | out Matches incoming or outgoing packets, respectively. in and out are mutually exclusive (in fact, out is implemented as not in). ipid id-list Matches IPv4 packets whose ip_id field has value included in id-list, which is either a single value or a list of values or ranges specified in the same way as ports. iplen len-list Matches IP packets whose total length, including header and data, is in the set len-list, which is either a single value or a list of values or ranges specified in the same way as ports. ipoptions spec Matches packets whose IPv4 header contains the comma separated list of options specified in spec. The supported IP options are: ssrr (strict source route), lsrr (loose source route), rr (record packet route) and ts (timestamp). The absence of a particular option may be denoted with a `!'. ipprecedence precedence Matches IPv4 packets whose precedence field is equal to precedence. ipsec Matches packets that have IPSEC history associated with them (i.e., the packet comes encapsulated in IPSEC, the kernel has IPSEC support, and can correctly decapsulate it). Note that specifying ipsec is different from specifying proto ipsec as the latter will only look at the specific IP protocol field, irrespective of IPSEC kernel support and the validity of the IPSEC data. Further note that this flag is silently ignored in kernels with- out IPSEC support. It does not affect rule processing when given and the rules are handled as if with no ipsec flag. iptos spec Matches IPv4 packets whose tos field contains the comma separated list of service types specified in spec. The supported IP types of service are: lowdelay (IPTOS_LOWDELAY), throughput (IPTOS_THROUGHPUT), reliability (IPTOS_RELIABILITY), mincost (IPTOS_MINCOST), congestion (IPTOS_ECN_CE). The absence of a particular type may be denoted with a `!'. dscp spec[,spec] Matches IPv4/IPv6 packets whose DS field value is contained in spec mask. Multiple values can be specified via the comma sepa- rated list. Value can be one of keywords used in setdscp action or exact number. ipttl ttl-list Matches IPv4 packets whose time to live is included in ttl-list, which is either a single value or a list of values or ranges specified in the same way as ports. ipversion ver Matches IP packets whose IP version field is ver. keep-state [:flowname] Upon a match, the firewall will create a dynamic rule, whose de- fault behaviour is to match bidirectional traffic between source and destination IP/port using the same protocol. The rule has a limited lifetime (controlled by a set of sysctl(8) variables), and the lifetime is refreshed every time a matching packet is found. The :flowname is used to assign additional to addresses, ports and protocol parameter to dynamic rule. It can be used for more accurate matching by check-state rule. The :default keyword is special name used for compatibility with old rulesets. layer2 Matches only layer2 packets, i.e., those passed to ipfw from ether_demux() and ether_output_frame(). limit {src-addr | src-port | dst-addr | dst-port} N [:flowname] The firewall will only allow N connections with the same set of parameters as specified in the rule. One or more of source and destination addresses and ports can be specified. lookup {dst-ip | dst-port | dst-mac | src-ip | src-port | src-mac | uid | jail} name Search an entry in lookup table name that matches the field spec- ified as argument. If not found, the match fails. Otherwise, the match succeeds and tablearg is set to the value extracted from the table. This option can be useful to quickly dispatch traffic based on certain packet fields. See the LOOKUP TABLES section below for more information on lookup tables. { MAC | mac } dst-mac src-mac Match packets with a given dst-mac and src-mac addresses, speci- fied as the any keyword (matching any MAC address), or six groups of hex digits separated by colons, and optionally followed by a mask indicating the significant bits. The mask may be specified using either of the following methods: 1. A slash (/) followed by the number of significant bits. For example, an address with 33 significant bits could be specified as: MAC 10:20:30:40:50:60/33 any 2. An ampersand (&) followed by a bitmask specified as six groups of hex digits separated by colons. For example, an address in which the last 16 bits are significant could be specified as: MAC 10:20:30:40:50:60&00:00:00:00:ff:ff any Note that the ampersand character has a special meaning in many shells and should generally be escaped. Note that the order of MAC addresses (destination first, source second) is the same as on the wire, but the opposite of the one used for IP addresses. mac-type mac-type Matches packets whose Ethernet Type field corresponds to one of those specified as argument. mac-type is specified in the same way as port numbers (i.e., one or more comma-separated single values or ranges). You can use symbolic names for known values such as vlan, ipv4, ipv6. Values can be entered as decimal or hexadecimal (if prefixed by 0x), and they are always printed as hexadecimal (unless the -N option is used, in which case symbolic resolution will be attempted). proto protocol Matches packets with the corresponding IP protocol. record-state Upon a match, the firewall will create a dynamic rule as if keep-state was specified. However, this option doesn't imply an implicit check-state in contrast to keep-state. recv | xmit | via {ifX | if* | table(name[,value]) | ipno | any} Matches packets received, transmitted or going through, respec- tively, the interface specified by exact name (ifX), by device name (if*), by IP address, or through some interface. Table name may be used to match interface by its kernel ifindex. See the LOOKUP TABLES section below for more information on lookup ta- bles. The via keyword causes the interface to always be checked. If recv or xmit is used instead of via, then only the receive or transmit interface (respectively) is checked. By specifying both, it is possible to match packets based on both receive and transmit interface, e.g.: ipfw add deny ip from any to any out recv ed0 xmit ed1 The recv interface can be tested on either incoming or outgoing packets, while the xmit interface can only be tested on outgoing packets. So out is required (and in is invalid) whenever xmit is used. A packet might not have a receive or transmit interface: packets originating from the local host have no receive interface, while packets destined for the local host have no transmit interface. set-limit {src-addr | src-port | dst-addr | dst-port} N Works like limit but does not have an implicit check-state at- tached to it. setup Matches TCP packets that have the SYN bit set but no ACK bit. This is the short form of "tcpflags syn,!ack". sockarg Matches packets that are associated to a local socket and for which the SO_USER_COOKIE socket option has been set to a non-zero value. As a side effect, the value of the option is made avail- able as tablearg value, which in turn can be used as skipto or pipe number. src-ip ip-address Matches IPv4 packets whose source IP is one of the address(es) specified as an argument. src-ip6 ip6-address Matches IPv6 packets whose source IP is one of the address(es) specified as an argument. src-port ports Matches IP packets whose source port is one of the port(s) speci- fied as argument. tagged tag-list Matches packets whose tags are included in tag-list, which is ei- ther a single value or a list of values or ranges specified in the same way as ports. Tags can be applied to the packet using tag rule action parameter (see it's description for details on tags). tcpack ack TCP packets only. Match if the TCP header acknowledgment number field is set to ack. tcpdatalen tcpdatalen-list Matches TCP packets whose length of TCP data is tcpdatalen-list, which is either a single value or a list of values or ranges specified in the same way as ports. tcpflags spec TCP packets only. Match if the TCP header contains the comma separated list of flags specified in spec. The supported TCP flags are: fin, syn, rst, psh, ack and urg. The absence of a particular flag may be denoted with a `!'. A rule which contains a tcpflags specification can never match a fragmented packet which has a non-zero offset. See the frag option for details on matching fragmented packets. tcpmss tcpmss-list Matches TCP packets whose MSS (maximum segment size) value is set to tcpmss-list, which is either a single value or a list of val- ues or ranges specified in the same way as ports. tcpseq seq TCP packets only. Match if the TCP header sequence number field is set to seq. tcpwin tcpwin-list Matches TCP packets whose header window field is set to tcpwin-list, which is either a single value or a list of values or ranges specified in the same way as ports. tcpoptions spec TCP packets only. Match if the TCP header contains the comma separated list of options specified in spec. The supported TCP options are: mss (maximum segment size), window (tcp window advertisement), sack (selective ack), ts (rfc1323 timestamp) and cc (rfc1644 t/tcp connection count). The absence of a particular option may be denoted with a `!'. uid user Match all TCP or UDP packets sent by or received for a user. A user may be matched by name or identification number. verrevpath For incoming packets, a routing table lookup is done on the packet's source address. If the interface on which the packet entered the system matches the outgoing interface for the route, the packet matches. If the interfaces do not match up, the packet does not match. All outgoing packets or packets with no incoming interface match. The name and functionality of the option is intentionally similar to the Cisco IOS command: ip verify unicast reverse-path This option can be used to make anti-spoofing rules to reject all packets with source addresses not from this interface. See also the option antispoof. versrcreach For incoming packets, a routing table lookup is done on the packet's source address. If a route to the source address ex- ists, but not the default route or a blackhole/reject route, the packet matches. Otherwise, the packet does not match. All out- going packets match. The name and functionality of the option is intentionally similar to the Cisco IOS command: ip verify unicast source reachable-via any This option can be used to make anti-spoofing rules to reject all packets whose source address is unreachable. antispoof For incoming packets, the packet's source address is checked if it belongs to a directly connected network. If the network is directly connected, then the interface the packet came on in is compared to the interface the network is connected to. When in- coming interface and directly connected interface are not the same, the packet does not match. Otherwise, the packet does match. All outgoing packets match. This option can be used to make anti-spoofing rules to reject all packets that pretend to be from a directly connected network but do not come in through that interface. This option is similar to but more restricted than verrevpath because it engages only on packets with source addresses of directly connected networks in- stead of all source addresses. LOOKUP TABLES Lookup tables are useful to handle large sparse sets of addresses or other search keys (e.g., ports, jail IDs, interface names). In the rest of this section we will use the term ``key''. Table name needs to match the following spec: table-name. Tables with the same name can be created in different sets. However, rule links to the tables in set 0 by de- fault. This behavior can be controlled by net.inet.ip.fw.tables_sets variable. See the SETS OF RULES section for more information. There may be up to 65535 different lookup tables. The following table types are supported: table-type: addr | iface | number | flow | mac table-key: addr[/masklen] | iface-name | number | flow-spec flow-spec: flow-field[,flow-spec] flow-field: src-ip | proto | src-port | dst-ip | dst-port addr Matches IPv4 or IPv6 address. Each entry is represented by an addr[/masklen] and will match all addresses with base addr (spec- ified as an IPv4/IPv6 address, or a hostname) and mask width of masklen bits. If masklen is not specified, it defaults to 32 for IPv4 and 128 for IPv6. When looking up an IP address in a table, the most specific entry will match. iface Matches interface names. Each entry is represented by string treated as interface name. Wildcards are not supported. number Matches protocol ports, uids/gids or jail IDs. Each entry is represented by 32-bit unsigned integer. Ranges are not sup- ported. flow Matches packet fields specified by flow type suboptions with ta- ble entries. mac Matches MAC address. Each entry is represented by an addr[/masklen] and will match all addresses with base addr and mask width of masklen bits. If masklen is not specified, it de- faults to 48. When looking up an MAC address in a table, the most specific entry will match. Tables require explicit creation via create before use. The following creation options are supported: create-options: create-option | create-options create-option: type table-type | valtype value-mask | algo algo-desc | limit number | locked | missing | or-flush type Table key type. valtype Table value mask. algo Table algorithm to use (see below). limit Maximum number of items that may be inserted into table. locked Restrict any table modifications. missing Do not fail if table already exists and has exactly same options as new one. or-flush Flush existing table with same name instead of returning error. Implies missing so existing table must be compatible with new one. Some of these options may be modified later via modify keyword. The fol- lowing options can be changed: modify-options: modify-option | modify-options modify-option: limit number limit Alter maximum number of items that may be inserted into table. Additionally, table can be locked or unlocked using lock or unlock com- mands. Tables of the same type can be swapped with each other using swap name command. Swap may fail if tables limits are set and data exchange would result in limits hit. Operation is performed atomically. One or more entries can be added to a table at once using add command. Addition of all items are performed atomically. By default, error in ad- dition of one entry does not influence addition of other entries. How- ever, non-zero error code is returned in that case. Special atomic key- word may be specified before add to indicate all-or-none add request. One or more entries can be removed from a table at once using delete com- mand. By default, error in removal of one entry does not influence re- moving of other entries. However, non-zero error code is returned in that case. It may be possible to check what entry will be found on particular table-key using lookup table-key command. This functionality is optional and may be unsupported in some algorithms. The following operations can be performed on one or all tables: list List all entries. flush Removes all entries. info Shows generic table information. detail Shows generic table information and algo-specific data. The following lookup algorithms are supported: algo-desc: algo-name | algo-name algo-data algo-name: addr: radix | addr: hash | iface: array | number: array | flow: hash | mac: radix addr: radix Separate Radix trees for IPv4 and IPv6, the same way as the rout- ing table (see route(4)). Default choice for addr type. addr:hash Separate auto-growing hashes for IPv4 and IPv6. Accepts entries with the same mask length specified initially via addr:hash masks=/v4,/v6 algorithm creation options. Assume /32 and /128 masks by default. Search removes host bits (according to mask) from supplied address and checks resulting key in appropriate hash. Mostly optimized for /64 and byte-ranged IPv6 masks. iface:array Array storing sorted indexes for entries which are presented in the system. Optimized for very fast lookup. number:array Array storing sorted u32 numbers. flow:hash Auto-growing hash storing flow entries. Search calculates hash on required packet fields and searches for matching entries in selected bucket. mac: radix Radix tree for MAC address The tablearg feature provides the ability to use a value, looked up in the table, as the argument for a rule action, action parameter or rule option. This can significantly reduce number of rules in some configura- tions. If two tables are used in a rule, the result of the second (des- tination) is used. Each record may hold one or more values according to value-mask. This mask is set on table creation via valtype option. The following value types are supported: value-mask: value-type[,value-mask] value-type: skipto | pipe | fib | nat | dscp | tag | divert | netgraph | limit | ipv4 skipto rule number to jump to. pipe Pipe number to use. fib fib number to match/set. nat nat number to jump to. dscp dscp value to match/set. tag tag number to match/set. divert port number to divert traffic to. netgraph hook number to move packet to. limit maximum number of connections. ipv4 IPv4 nexthop to fwd packets to. ipv6 IPv6 nexthop to fwd packets to. The tablearg argument can be used with the following actions: nat, pipe, queue, divert, tee, netgraph, ngtee, fwd, skipto, setfib, action parame- ters: tag, untag, rule options: limit, tagged. When used with the skipto action, the user should be aware that the code will walk the ruleset up to a rule equal to, or past, the given number. See the EXAMPLES Section for example usage of tables and the tablearg keyword. SETS OF RULES Each rule or table belongs to one of 32 different sets , numbered 0 to 31. Set 31 is reserved for the default rule. By default, rules or tables are put in set 0, unless you use the set N attribute when adding a new rule or table. Sets can be individually and atomically enabled or disabled, so this mechanism permits an easy way to store multiple configurations of the firewall and quickly (and atomi- cally) switch between them. By default, tables from set 0 are referenced when adding rule with table opcodes regardless of rule set. This behavior can be changed by setting net.inet.ip.fw.tables_sets variable to 1. Rule's set will then be used for table references. The command to enable/disable sets is ipfw set [disable number ...] [enable number ...] where multiple enable or disable sections can be specified. Command exe- cution is atomic on all the sets specified in the command. By default, all sets are enabled. When you disable a set, its rules behave as if they do not exist in the firewall configuration, with only one exception: dynamic rules created from a rule before it had been disabled will still be active until they expire. In order to delete dynamic rules you have to explicitly delete the parent rule which generated them. The set number of rules can be changed with the command ipfw set move {rule rule-number | old-set} to new-set Also, you can atomically swap two rulesets with the command ipfw set swap first-set second-set See the EXAMPLES Section on some possible uses of sets of rules. STATEFUL FIREWALL Stateful operation is a way for the firewall to dynamically create rules for specific flows when packets that match a given pattern are detected. Support for stateful operation comes through the check-state, keep-state, record-state, limit and set-limit options of rules. Dynamic rules are created when a packet matches a keep-state, record-state, limit or set-limit rule, causing the creation of a dynamic rule which will match all and only packets with a given protocol between a src-ip/src-port dst-ip/dst-port pair of addresses (src and dst are used here only to denote the initial match addresses, but they are completely equivalent afterwards). Rules created by keep-state option also have a :flowname taken from it. This name is used in matching together with ad- dresses, ports and protocol. Dynamic rules will be checked at the first check-state, keep-state or limit occurrence, and the action performed upon a match will be the same as in the parent rule. Note that no additional attributes other than protocol and IP addresses and ports and :flowname are checked on dynamic rules. The typical use of dynamic rules is to keep a closed firewall configura- tion, but let the first TCP SYN packet from the inside network install a dynamic rule for the flow so that packets belonging to that session will be allowed through the firewall: ipfw add check-state :OUTBOUND ipfw add allow tcp from my-subnet to any setup keep-state :OUTBOUND ipfw add deny tcp from any to any A similar approach can be used for UDP, where an UDP packet coming from the inside will install a dynamic rule to let the response through the firewall: ipfw add check-state :OUTBOUND ipfw add allow udp from my-subnet to any keep-state :OUTBOUND ipfw add deny udp from any to any Dynamic rules expire after some time, which depends on the status of the flow and the setting of some sysctl variables. See Section SYSCTL VARIABLES for more details. For TCP sessions, dynamic rules can be in- structed to periodically send keepalive packets to refresh the state of the rule when it is about to expire. See Section EXAMPLES for more examples on how to use dynamic rules. TRAFFIC SHAPER (DUMMYNET) CONFIGURATION ipfw is also the user interface for the dummynet traffic shaper, packet scheduler and network emulator, a subsystem that can artificially queue, delay or drop packets emulating the behaviour of certain network links or queueing systems. dummynet operates by first using the firewall to select packets using any match pattern that can be used in ipfw rules. Matching packets are then passed to either of two different objects, which implement the traffic regulation: pipe A pipe emulates a link with given bandwidth and propagation delay, driven by a FIFO scheduler and a single queue with programmable queue size and packet loss rate. Packets are appended to the queue as they come out from ipfw, and then transferred in FIFO order to the link at the desired rate. queue A queue is an abstraction used to implement packet scheduling using one of several packet scheduling algorithms. Packets sent to a queue are first grouped into flows according to a mask on the 5-tuple. Flows are then passed to the scheduler associated to the queue, and each flow uses scheduling param- eters (weight and others) as configured in the queue itself. A scheduler in turn is connected to an emulated link, and ar- bitrates the link's bandwidth among backlogged flows accord- ing to weights and to the features of the scheduling algo- rithm in use. In practice, pipes can be used to set hard limits to the bandwidth that a flow can use, whereas queues can be used to determine how different flows share the available bandwidth. A graphical representation of the binding of queues, flows, schedulers and links is below. (flow_mask|sched_mask) sched_mask +---------+ weight Wx +-------------+ | |->-[flow]-->--| |-+ -->--| QUEUE x | ... | | | | |->-[flow]-->--| SCHEDuler N | | +---------+ | | | ... | +--[LINK N]-->-- +---------+ weight Wy | | +--[LINK N]-->-- | |->-[flow]-->--| | | -->--| QUEUE y | ... | | | | |->-[flow]-->--| | | +---------+ +-------------+ | +-------------+ It is important to understand the role of the SCHED_MASK and FLOW_MASK, which are configured through the commands ipfw sched N config mask SCHED_MASK ... and ipfw queue X config mask FLOW_MASK .... The SCHED_MASK is used to assign flows to one or more scheduler in- stances, one for each value of the packet's 5-tuple after applying SCHED_MASK. As an example, using ``src-ip 0xffffff00'' creates one in- stance for each /24 destination subnet. The FLOW_MASK, together with the SCHED_MASK, is used to split packets into flows. As an example, using ``src-ip 0x000000ff'' together with the previous SCHED_MASK makes a flow for each individual source address. In turn, flows for each /24 subnet will be sent to the same scheduler in- stance. The above diagram holds even for the pipe case, with the only restriction that a pipe only supports a SCHED_MASK, and forces the use of a FIFO scheduler (these are for backward compatibility reasons; in fact, inter- nally, a dummynet's pipe is implemented exactly as above). There are two modes of dummynet operation: "normal" and "fast". The "normal" mode tries to emulate a real link: the dummynet scheduler en- sures that the packet will not leave the pipe faster than it would on the real link with a given bandwidth. The "fast" mode allows certain packets to bypass the dummynet scheduler (if packet flow does not exceed pipe's bandwidth). This is the reason why the "fast" mode requires less CPU cy- cles per packet (on average) and packet latency can be significantly lower in comparison to a real link with the same bandwidth. The default mode is "normal". The "fast" mode can be enabled by setting the net.inet.ip.dummynet.io_fast sysctl(8) variable to a non-zero value. PIPE, QUEUE AND SCHEDULER CONFIGURATION The pipe, queue and scheduler configuration commands are the following: pipe number config pipe-configuration queue number config queue-configuration sched number config sched-configuration The following parameters can be configured for a pipe: bw bandwidth | device Bandwidth, measured in [K|M|G]{bit/s|Byte/s}. A value of 0 (default) means unlimited bandwidth. The unit must immediately follow the number, as in dnctl pipe 1 config bw 300Kbit/s If a device name is specified instead of a numeric value, as in dnctl pipe 1 config bw tun0 then the transmit clock is supplied by the specified device. At the moment only the tun(4) device supports this functionality, for use in conjunction with ppp(8). delay ms-delay Propagation delay, measured in milliseconds. The value is rounded to the next multiple of the clock tick (typically 10ms, but it is a good practice to run kernels with "options HZ=1000" to reduce the granularity to 1ms or less). The default value is 0, meaning no delay. burst size If the data to be sent exceeds the pipe's bandwidth limit (and the pipe was previously idle), up to size bytes of data are al- lowed to bypass the dummynet scheduler, and will be sent as fast as the physical link allows. Any additional data will be trans- mitted at the rate specified by the pipe bandwidth. The burst size depends on how long the pipe has been idle; the effective burst size is calculated as follows: MAX( size , bw * pipe_idle_time). profile filename A file specifying the additional overhead incurred in the trans- mission of a packet on the link. Some link types introduce extra delays in the transmission of a packet, e.g., because of MAC level framing, contention on the use of the channel, MAC level retransmissions and so on. From our point of view, the channel is effectively unavailable for this extra time, which is constant or variable depending on the link type. Additionally, packets may be dropped after this time (e.g., on a wireless link after too many retransmissions). We can model the additional delay with an empirical curve that rep- resents its distribution. cumulative probability 1.0 ^ | L +-- loss-level x | ****** | * | ***** | * | ** | * +-------*-------------------> delay The empirical curve may have both vertical and horizontal lines. Vertical lines represent constant delay for a range of probabili- ties. Horizontal lines correspond to a discontinuity in the de- lay distribution: the pipe will use the largest delay for a given probability. The file format is the following, with whitespace acting as a separator and '#' indicating the beginning a comment: name identifier optional name (listed by "dnctl pipe show") to identify the delay distribution; bw value the bandwidth used for the pipe. If not specified here, it must be present explicitly as a configuration parame- ter for the pipe; loss-level L the probability above which packets are lost. (0.0 <= L <= 1.0, default 1.0 i.e., no loss); samples N the number of samples used in the internal representation of the curve (2..1024; default 100); delay prob | prob delay One of these two lines is mandatory and defines the for- mat of the following lines with data points. XXX YYY 2 or more lines representing points in the curve, with either delay or probability first, according to the cho- sen format. The unit for delay is milliseconds. Data points do not need to be sorted. Also, the number of ac- tual lines can be different from the value of the "sam- ples" parameter: ipfw utility will sort and interpolate the curve as needed. Example of a profile file: name bla_bla_bla samples 100 loss-level 0.86 prob delay 0 200 # minimum overhead is 200ms 0.5 200 0.5 300 0.8 1000 0.9 1300 1 1300 #configuration file end The following parameters can be configured for a queue: pipe pipe_nr Connects a queue to the specified pipe. Multiple queues (with the same or different weights) can be connected to the same pipe, which specifies the aggregate rate for the set of queues. weight weight Specifies the weight to be used for flows matching this queue. The weight must be in the range 1..100, and defaults to 1. The following case-insensitive parameters can be configured for a sched- uler: type {fifo | wf2q+ | rr | qfq | fq_codel | fq_pie} specifies the scheduling algorithm to use. fifo is just a FIFO scheduler (which means that all packets are stored in the same queue as they arrive to the sched- uler). FIFO has O(1) per-packet time complexity, with very low constants (estimate 60-80ns on a 2GHz desktop machine) but gives no service guarantees. wf2q+ implements the WF2Q+ algorithm, which is a Weighted Fair Queueing algorithm which permits flows to share bandwidth according to their weights. Note that weights are not priorities; even a flow with a minuscule weight will never starve. WF2Q+ has O(log N) per-packet processing cost, where N is the number of flows, and is the default algorithm used by previous versions dummynet's queues. rr implements the Deficit Round Robin algorithm, which has O(1) processing costs (roughly, 100-150ns per packet) and permits bandwidth allocation according to weights, but with poor service guarantees. qfq implements the QFQ algorithm, which is a very fast vari- ant of WF2Q+, with similar service guarantees and O(1) processing costs (roughly, 200-250ns per packet). fq_codel implements the FQ-CoDel (FlowQueue-CoDel) scheduler/AQM algorithm, which uses a modified Deficit Round Robin scheduler to manage two lists of sub-queues (old sub- queues and new sub-queues) for providing brief periods of priority to lightweight or short burst flows. By de- fault, the total number of sub-queues is 1024. FQ- CoDel's internal, dynamically created sub-queues are con- trolled by separate instances of CoDel AQM. fq_pie implements the FQ-PIE (FlowQueue-PIE) scheduler/AQM algo- rithm, which similar to fq_codel but uses per sub-queue PIE AQM instance to control the queue delay. fq_codel inherits AQM parameters and options from codel (see be- low), and fq_pie inherits AQM parameters and options from pie (see below). Additionally, both of fq_codel and fq_pie have shared scheduler parameters which are: quantum m specifies the quantum (credit) of the scheduler. m is the number of bytes a queue can serve before being moved to the tail of old queues list. The default is 1514 bytes, and the maximum acceptable value is 9000 bytes. limit m specifies the hard size limit (in unit of packets) of all queues managed by an instance of the scheduler. The default value of m is 10240 packets, and the maximum ac- ceptable value is 20480 packets. flows m specifies the total number of flow queues (sub-queues) that fq_* creates and manages. By default, 1024 sub- queues are created when an instance of the fq_{codel/pie} scheduler is created. The maximum acceptable value is 65536. Note that any token after fq_codel or fq_pie is considered a pa- rameter for fq_{codel/pie}. So, ensure all scheduler configura- tion options not related to fq_{codel/pie} are written before fq_codel/fq_pie tokens. In addition to the type, all parameters allowed for a pipe can also be specified for a scheduler. Finally, the following parameters can be configured for both pipes and queues: buckets hash-table-size Specifies the size of the hash table used for storing the various queues. Default value is 64 controlled by the sysctl(8) variable net.inet.ip.dummynet.hash_size, allowed range is 16 to 65536. mask mask-specifier Packets sent to a given pipe or queue by an ipfw rule can be fur- ther classified into multiple flows, each of which is then sent to a different dynamic pipe or queue. A flow identifier is construc- ted by masking the IP addresses, ports and protocol types as speci- fied with the mask options in the configuration of the pipe or queue. For each different flow identifier, a new pipe or queue is created with the same parameters as the original object, and match- ing packets are sent to it. Thus, when dynamic pipes are used, each flow will get the same bandwidth as defined by the pipe, whereas when dynamic queues are used, each flow will share the parent's pipe bandwidth evenly with other flows generated by the same queue (note that other queues with different weights might be connected to the same pipe). Available mask specifiers are a combination of one or more of the following: dst-ip mask, dst-ip6 mask, src-ip mask, src-ip6 mask, dst-port mask, src-port mask, flow-id mask, proto mask or all, where the latter means all bits in all fields are significant. noerror When a packet is dropped by a dummynet queue or pipe, the error is normally reported to the caller routine in the kernel, in the same way as it happens when a device queue fills up. Setting this op- tion reports the packet as successfully delivered, which can be needed for some experimental setups where you want to simulate loss or congestion at a remote router. plr packet-loss-rate Packet loss rate. Argument packet-loss-rate is a floating-point number between 0 and 1, with 0 meaning no loss, 1 meaning 100% loss. The loss rate is internally represented on 31 bits. queue {slots | sizeKbytes} Queue size, in slots or KBytes. Default value is 50 slots, which is the typical queue size for Ethernet devices. Note that for slow speed links you should keep the queue size short or your traffic might be affected by a significant queueing delay. E.g., 50 max- sized Ethernet packets (1500 bytes) mean 600Kbit or 20s of queue on a 30Kbit/s pipe. Even worse effects can result if you get packets from an interface with a much larger MTU, e.g. the loopback inter- face with its 16KB packets. The sysctl(8) variables net.inet.ip.dummynet.pipe_byte_limit and net.inet.ip.dummynet.pipe_slot_limit control the maximum lengths that can be specified. red | gred w_q/min_th/max_th/max_p [ecn] Make use of the RED (Random Early Detection) queue management algorithm. w_q and max_p are floating point numbers between 0 and 1 (inclusive), while min_th and max_th are integer numbers specify- ing thresholds for queue management (thresholds are computed in bytes if the queue has been defined in bytes, in slots otherwise). The two parameters can also be of the same value if needed. The dummynet also supports the gentle RED variant (gred) and ECN (Ex- plicit Congestion Notification) as optional. Three sysctl(8) vari- ables can be used to control the RED behaviour: net.inet.ip.dummynet.red_lookup_depth specifies the accuracy in computing the average queue when the link is idle (defaults to 256, must be greater than zero) net.inet.ip.dummynet.red_avg_pkt_size specifies the expected average packet size (defaults to 512, must be greater than zero) net.inet.ip.dummynet.red_max_pkt_size specifies the expected maximum packet size, only used when queue thresholds are in bytes (defaults to 1500, must be greater than zero). codel [target time] [interval time] [ecn | noecn] Make use of the CoDel (Controlled-Delay) queue management algo- rithm. time is interpreted as milliseconds by default but seconds (s), milliseconds (ms) or microseconds (us) can be specified in- stead. CoDel drops or marks (ECN) packets depending on packet so- journ time in the queue. target time (5ms by default) is the mini- mum acceptable persistent queue delay that CoDel allows. CoDel does not drop packets directly after packets sojourn time becomes higher than target time but waits for interval time (100ms default) before dropping. interval time should be set to maximum RTT for all expected connections. ecn enables (disabled by default) packet marking (instead of dropping) for ECN-enabled TCP flows when queue delay becomes high. Note that any token after codel is considered a parameter for CoDel. So, ensure all pipe/queue configuration options are written before codel token. The sysctl(8) variables net.inet.ip.dummynet.codel.target and net.inet.ip.dummynet.codel.interval can be used to set CoDel de- fault parameters. pie [target time] [tupdate time] [alpha n] [beta n] [max_burst time] [max_ecnth n] [ecn | noecn] [capdrop | nocapdrop] [drand | nodrand] [onoff] [dre | ts] Make use of the PIE (Proportional Integral controller Enhanced) queue management algorithm. PIE drops or marks packets depending on a calculated drop probability during en-queue process, with the aim of achieving high throughput while keeping queue delay low. At regular time intervals of tupdate time (15ms by default) a back- ground process (re)calculates the probability based on queue delay deviations from target time (15ms by default) and queue delay trends. PIE approximates current queue delay by using a departure rate estimation method, or (optionally) by using a packet timestamp method similar to CoDel. time is interpreted as milliseconds by default but seconds (s), milliseconds (ms) or microseconds (us) can be specified instead. The other PIE parameters and options are as follows: alpha n n is a floating point number between 0 and 7 which speci- fies the weight of queue delay deviations that is used in drop probability calculation. 0.125 is the default. beta n n is a floating point number between 0 and 7 which speci- fies is the weight of queue delay trend that is used in drop probability calculation. 1.25 is the default. max_burst time The maximum period of time that PIE does not drop/mark packets. 150ms is the default and 10s is the maximum value. max_ecnth n Even when ECN is enabled, PIE drops packets instead of marking them when drop probability becomes higher than ECN probability threshold max_ecnth n , the default is 0.1 (i.e 10%) and 1 is the maximum value. ecn | noecn enable or disable ECN marking for ECN-enabled TCP flows. Disabled by default. capdrop | nocapdrop enable or disable cap drop adjustment. Cap drop adjustment is enabled by default. drand | nodrand enable or disable drop probability de-randomisation. De- randomisation eliminates the problem of dropping packets too close or too far. De-randomisation is enabled by de- fault. onoff enable turning PIE on and off depending on queue load. If this option is enabled, PIE turns on when over 1/3 of queue becomes full. This option is disabled by default. dre | ts Calculate queue delay using departure rate estimation dre or timestamps ts. dre is used by default. Note that any token after pie is considered a parameter for PIE. So ensure all pipe/queue the configuration options are written be- fore pie token. sysctl(8) variables can be used to control the pie default parameters. See the SYSCTL VARIABLES section for more de- tails. When used with IPv6 data, dummynet currently has several limitations. Information necessary to route link-local packets to an interface is not available after processing by dummynet so those packets are dropped in the output path. Care should be taken to ensure that link-local packets are not passed to dummynet. CHECKLIST Here are some important points to consider when designing your rules: o Remember that you filter both packets going in and out. Most connec- tions need packets going in both directions. o Remember to test very carefully. It is a good idea to be near the console when doing this. If you cannot be near the console, use an auto-recovery script such as the one in /usr/share/examples/ipfw/change_rules.sh. o Do not forget the loopback interface. FINE POINTS o There are circumstances where fragmented datagrams are uncondition- ally dropped. TCP packets are dropped if they do not contain at least 20 bytes of TCP header, UDP packets are dropped if they do not contain a full 8 byte UDP header, and ICMP packets are dropped if they do not contain 4 bytes of ICMP header, enough to specify the ICMP type, code, and checksum. These packets are simply logged as "pullup failed" since there may not be enough good data in the packet to produce a meaningful log entry. o Another type of packet is unconditionally dropped, a TCP packet with a fragment offset of one. This is a valid packet, but it only has one use, to try to circumvent firewalls. When logging is enabled, these packets are reported as being dropped by rule -1. o If you are logged in over a network, loading the kld(4) version of ipfw is probably not as straightforward as you would think. The fol- lowing command line is recommended: kldload ipfw && \ ipfw add 32000 allow ip from any to any Along the same lines, doing an ipfw flush in similar surroundings is also a bad idea. o The ipfw filter list may not be modified if the system security level is set to 3 or higher (see init(8) for information on system security levels). PACKET DIVERSION A divert(4) socket bound to the specified port will receive all packets diverted to that port. If no socket is bound to the destination port, or if the divert module is not loaded, or if the kernel was not compiled with divert socket support, the packets are dropped. NETWORK ADDRESS TRANSLATION (NAT) ipfw support in-kernel NAT using the kernel version of libalias(3). The kernel module ipfw_nat should be loaded or kernel should have options IPFIREWALL_NAT to be able use NAT. The nat configuration command is the following: nat nat_number config nat-configuration The following parameters can be configured: ip ip_address Define an ip address to use for aliasing. if nic Use ip address of NIC for aliasing, dynamically changing it if NIC's ip address changes. log Enable logging on this nat instance. deny_in Deny any incoming connection from outside world. same_ports Try to leave the alias port numbers unchanged from the actual lo- cal port numbers. unreg_only Traffic on the local network not originating from a RFC 1918 un- registered address spaces will be ignored. unreg_cgn Like unreg_only, but includes the RFC 6598 (Carrier Grade NAT) address range. reset Reset table of the packet aliasing engine on address change. reverse Reverse the way libalias handles aliasing. proxy_only Obey transparent proxy rules only, packet aliasing is not per- formed. skip_global Skip instance in case of global state lookup (see below). port_range lower-upper Set the aliasing ports between the ranges given. Upper port has to be greater than lower. Some special values can be supplied instead of nat_number in nat rule ac- tions: global Looks up translation state in all configured nat instances. If an entry is found, packet is aliased according to that entry. If no entry was found in any of the instances, packet is passed un- changed, and no new entry will be created. See section MULTIPLE INSTANCES in natd(8) for more information. tablearg Uses argument supplied in lookup table. See LOOKUP TABLES sec- tion below for more information on lookup tables. To let the packet continue after being (de)aliased, set the sysctl vari- able net.inet.ip.fw.one_pass to 0. For more information about aliasing modes, refer to libalias(3). See Section EXAMPLES for some examples of nat usage. REDIRECT AND LSNAT SUPPORT IN IPFW Redirect and LSNAT support follow closely the syntax used in natd(8). See Section EXAMPLES for some examples on how to do redirect and lsnat. SCTP NAT SUPPORT SCTP nat can be configured in a similar manner to TCP through the ipfw command line tool. The main difference is that sctp nat does not do port translation. Since the local and global side ports will be the same, there is no need to specify both. Ports are redirected as follows: nat nat_number config if nic redirect_port sctp ip_address [,addr_list] {[port | port-port] [,ports]} Most sctp nat configuration can be done in real-time through the sysctl(8) interface. All may be changed dynamically, though the hash_ta- ble size will only change for new nat instances. See SYSCTL VARIABLES for more info. IPv6/IPv4 NETWORK ADDRESS AND PROTOCOL TRANSLATION Stateful translation ipfw supports in-kernel IPv6/IPv4 network address and protocol transla- tion. Stateful NAT64 translation allows IPv6-only clients to contact IPv4 servers using unicast TCP, UDP or ICMP protocols. One or more IPv4 addresses assigned to a stateful NAT64 translator are shared among sev- eral IPv6-only clients. When stateful NAT64 is used in conjunction with DNS64, no changes are usually required in the IPv6 client or the IPv4 server. The kernel module ipfw_nat64 should be loaded or kernel should have options IPFIREWALL_NAT64 to be able use stateful NAT64 translator. Stateful NAT64 uses a bunch of memory for several types of objects. When IPv6 client initiates connection, NAT64 translator creates a host entry in the states table. Each host entry uses preallocated IPv4 alias entry. Each alias entry has a number of ports group entries allocated on demand. Ports group entries contains connection state entries. There are several options to control limits and lifetime for these objects. NAT64 translator follows RFC7915 when does ICMPv6/ICMP translation, un- supported message types will be silently dropped. IPv6 needs several ICMPv6 message types to be explicitly allowed for correct operation. Make sure that ND6 neighbor solicitation (ICMPv6 type 135) and neighbor advertisement (ICMPv6 type 136) messages will not be handled by transla- tion rules. After translation NAT64 translator by default sends packets through cor- responding netisr queue. Thus translator host should be configured as IPv4 and IPv6 router. Also this means, that a packet is handled by fire- wall twice. First time an original packet is handled and consumed by translator, and then it is handled again as translated packet. This be- havior can be changed by sysctl variable net.inet.ip.fw.nat64_direct_output. Also translated packet can be tagged using tag rule action, and then matched by tagged opcode to avoid loops and extra overhead. The stateful NAT64 configuration command is the following: nat64lsn name create create-options The following parameters can be configured: prefix4 ipv4_prefix/plen The IPv4 prefix with mask defines the pool of IPv4 addresses used as source address after translation. Stateful NAT64 module translates IPv6 source address of client to one IPv4 address from this pool. Note that incoming IPv4 packets that don't have cor- responding state entry in the states table will be dropped by translator. Make sure that translation rules handle packets, destined to configured prefix. prefix6 ipv6_prefix/length The IPv6 prefix defines IPv4-embedded IPv6 addresses used by translator to represent IPv4 addresses. This IPv6 prefix should be configured in DNS64. The translator implementation follows RFC6052, that restricts the length of prefixes to one of follow- ing: 32, 40, 48, 56, 64, or 96. The Well-Known IPv6 Prefix 64:ff9b:: must be 96 bits long. The special ::/length prefix can be used to handle several IPv6 prefixes with one NAT64 instance. The NAT64 instance will determine a destination IPv4 address from prefix length. states_chunks number The number of states chunks in single ports group. Each ports group by default can keep 64 state entries in single chunk. The above value affects the maximum number of states that can be as- sociated with single IPv4 alias address and port. The value must be power of 2, and up to 128. host_del_age seconds The number of seconds until the host entry for a IPv6 client will be deleted and all its resources will be released due to inactiv- ity. Default value is 3600. pg_del_age seconds The number of seconds until a ports group with unused state en- tries will be released. Default value is 900. tcp_syn_age seconds The number of seconds while a state entry for TCP connection with only SYN sent will be kept. If TCP connection establishing will not be finished, state entry will be deleted. Default value is 10. tcp_est_age seconds The number of seconds while a state entry for established TCP connection will be kept. Default value is 7200. tcp_close_age seconds The number of seconds while a state entry for closed TCP connec- tion will be kept. Keeping state entries for closed connections is needed, because IPv4 servers typically keep closed connections in a TIME_WAIT state for a several minutes. Since translator's IPv4 addresses are shared among all IPv6 clients, new connections from the same addresses and ports may be rejected by server, be- cause these connections are still in a TIME_WAIT state. Keeping them in translator's state table protects from such rejects. De- fault value is 180. udp_age seconds The number of seconds while translator keeps state entry in a waiting for reply to the sent UDP datagram. Default value is 120. icmp_age seconds The number of seconds while translator keeps state entry in a waiting for reply to the sent ICMP message. Default value is 60. log Turn on logging of all handled packets via BPF through ipfwlog0 interface. ipfwlog0 is a pseudo interface and can be created af- ter a boot manually with ifconfig command. Note that it has dif- ferent purpose than ipfw0 interface. Translators sends to BPF an additional information with each packet. With tcpdump you are able to see each handled packet before and after translation. -log Turn off logging of all handled packets via BPF. allow_private Turn on processing private IPv4 addresses. By default IPv6 pack- ets with destinations mapped to private address ranges defined by RFC1918 are not processed. -allow_private Turn off private address handling in nat64 instance. To inspect a states table of stateful NAT64 the following command can be used: nat64lsn name show states Stateless NAT64 translator doesn't use a states table for translation and converts IPv4 addresses to IPv6 and vice versa solely based on the map- pings taken from configured lookup tables. Since a states table doesn't used by stateless translator, it can be configured to pass IPv4 clients to IPv6-only servers. The stateless NAT64 configuration command is the following: nat64stl name create create-options The following parameters can be configured: prefix6 ipv6_prefix/length The IPv6 prefix defines IPv4-embedded IPv6 addresses used by translator to represent IPv4 addresses. This IPv6 prefix should be configured in DNS64. table4 table46 The lookup table table46 contains mapping how IPv4 addresses should be translated to IPv6 addresses. table6 table64 The lookup table table64 contains mapping how IPv6 addresses should be translated to IPv4 addresses. log Turn on logging of all handled packets via BPF through ipfwlog0 interface. -log Turn off logging of all handled packets via BPF. allow_private Turn on processing private IPv4 addresses. By default IPv6 pack- ets with destinations mapped to private address ranges defined by RFC1918 are not processed. -allow_private Turn off private address handling in nat64 instance. Note that the behavior of stateless translator with respect to not matched packets differs from stateful translator. If corresponding ad- dresses was not found in the lookup tables, the packet will not be dropped and the search continues. XLAT464 CLAT translation XLAT464 CLAT NAT64 translator implements client-side stateless transla- tion as defined in RFC6877 and is very similar to statless NAT64 transla- tor explained above. Instead of lookup tables it uses one-to-one mapping between IPv4 and IPv6 addresses using configured prefixes. This mode can be used as a replacement of DNS64 service for applications that are not using it (e.g. VoIP) allowing them to access IPv4-only Internet over IPv6-only networks with help of remote NAT64 translator. The CLAT NAT64 configuration command is the following: nat64clat name create create-options The following parameters can be configured: clat_prefix ipv6_prefix/length The IPv6 prefix defines IPv4-embedded IPv6 addresses used by translator to represent source IPv4 addresses. plat_prefix ipv6_prefix/length The IPv6 prefix defines IPv4-embedded IPv6 addresses used by translator to represent destination IPv4 addresses. This IPv6 prefix should be configured on a remote NAT64 translator. log Turn on logging of all handled packets via BPF through ipfwlog0 interface. -log Turn off logging of all handled packets via BPF. allow_private Turn on processing private IPv4 addresses. By default nat64clat instance will not process IPv4 packets with destination address from private ranges as defined in RFC1918. -allow_private Turn off private address handling in nat64clat instance. Note that the behavior of CLAT translator with respect to not matched packets differs from stateful translator. If corresponding addresses were not matched against prefixes configured, the packet will not be dropped and the search continues. IPv6-to-IPv6 NETWORK PREFIX TRANSLATION (NPTv6) ipfw supports in-kernel IPv6-to-IPv6 network prefix translation as de- scribed in RFC6296. The kernel module ipfw_nptv6 should be loaded or kernel should has options IPFIREWALL_NPTV6 to be able use NPTv6 transla- tor. The NPTv6 configuration command is the following: nptv6 name create create-options The following parameters can be configured: int_prefix ipv6_prefix IPv6 prefix used in internal network. NPTv6 module translates source address when it matches this prefix. ext_prefix ipv6_prefix IPv6 prefix used in external network. NPTv6 module translates destination address when it matches this prefix. ext_if nic The NPTv6 module will use first global IPv6 address from inter- face nic as external prefix. It can be useful when IPv6 prefix of external network is dynamically obtained. ext_prefix and ext_if options are mutually exclusive. prefixlen length The length of specified IPv6 prefixes. It must be in range from 8 to 64. Note that the prefix translation rules are silently ignored when IPv6 packet forwarding is disabled. To enable the packet forwarding, set the sysctl variable net.inet6.ip6.forwarding to 1. To let the packet continue after being translated, set the sysctl vari- able net.inet.ip.fw.one_pass to 0. LOADER TUNABLES Tunables can be set in loader(8) prompt, loader.conf(5) or kenv(1) before ipfw module gets loaded. net.inet.ip.fw.default_to_accept: 0 Defines ipfw last rule behavior. This value overrides options IPFW_DEFAULT_TO_(ACCEPT|DENY) from kernel configuration file. net.inet.ip.fw.tables_max: 128 Defines number of tables available in ipfw. Number cannot exceed 65534. SYSCTL VARIABLES A set of sysctl(8) variables controls the behaviour of the firewall and associated modules (dummynet, bridge, sctp nat). These are shown below together with their default value (but always check with the sysctl(8) command what value is actually in use) and meaning: net.inet.ip.alias.sctp.accept_global_ootb_addip: 0 Defines how the nat responds to receipt of global OOTB ASCONF-Ad- dIP: 0 No response (unless a partially matching association ex- ists - ports and vtags match but global address does not) 1 nat will accept and process all OOTB global AddIP mes- sages. Option 1 should never be selected as this forms a security risk. An attacker can establish multiple fake associations by sending AddIP messages. net.inet.ip.alias.sctp.chunk_proc_limit: 5 Defines the maximum number of chunks in an SCTP packet that will be parsed for a packet that matches an existing association. This value is enforced to be greater or equal than net.inet.ip.alias.sctp.initialising_chunk_proc_limit. A high value is a DoS risk yet setting too low a value may result in im- portant control chunks in the packet not being located and parsed. net.inet.ip.alias.sctp.error_on_ootb: 1 Defines when the nat responds to any Out-of-the-Blue (OOTB) pack- ets with ErrorM packets. An OOTB packet is a packet that arrives with no existing association registered in the nat and is not an INIT or ASCONF-AddIP packet: 0 ErrorM is never sent in response to OOTB packets. 1 ErrorM is only sent to OOTB packets received on the local side. 2 ErrorM is sent to the local side and on the global side ONLY if there is a partial match (ports and vtags match but the source global IP does not). This value is only useful if the nat is tracking global IP addresses. 3 ErrorM is sent in response to all OOTB packets on both the local and global side (DoS risk). At the moment the default is 0, since the ErrorM packet is not yet supported by most SCTP stacks. When it is supported, and if not tracking global addresses, we recommend setting this value to 1 to allow multi-homed local hosts to function with the nat. To track global addresses, we recommend setting this value to 2 to allow global hosts to be informed when they need to (re)send an ASCONF-AddIP. Value 3 should never be chosen (except for debug- ging) as the nat will respond to all OOTB global packets (a DoS risk). net.inet.ip.alias.sctp.hashtable_size: 2003 Size of hash tables used for nat lookups (100 < prime_number > 1000001). This value sets the hash table size for any future created nat instance and therefore must be set prior to creating a nat instance. The table sizes may be changed to suit specific needs. If there will be few concurrent associations, and memory is scarce, you may make these smaller. If there will be many thousands (or millions) of concurrent associations, you should make these larger. A prime number is best for the table size. The sysctl update function will adjust your input value to the next highest prime number. net.inet.ip.alias.sctp.holddown_time: 0 Hold association in table for this many seconds after receiving a SHUTDOWN-COMPLETE. This allows endpoints to correct shutdown gracefully if a shutdown_complete is lost and retransmissions are required. net.inet.ip.alias.sctp.init_timer: 15 Timeout value while waiting for (INIT-ACK|AddIP-ACK). This value cannot be 0. net.inet.ip.alias.sctp.initialising_chunk_proc_limit: 2 Defines the maximum number of chunks in an SCTP packet that will be parsed when no existing association exists that matches that packet. Ideally this packet will only be an INIT or ASCONF-AddIP packet. A higher value may become a DoS risk as malformed pack- ets can consume processing resources. net.inet.ip.alias.sctp.param_proc_limit: 25 Defines the maximum number of parameters within a chunk that will be parsed in a packet. As for other similar sysctl variables, larger values pose a DoS risk. net.inet.ip.alias.sctp.log_level: 0 Level of detail in the system log messages (0 - minimal, 1 - event, 2 - info, 3 - detail, 4 - debug, 5 - max debug). May be a good option in high loss environments. net.inet.ip.alias.sctp.shutdown_time: 15 Timeout value while waiting for SHUTDOWN-COMPLETE. This value cannot be 0. net.inet.ip.alias.sctp.track_global_addresses: 0 Enables/disables global IP address tracking within the nat and places an upper limit on the number of addresses tracked for each association: 0 Global tracking is disabled >1 Enables tracking, the maximum number of addresses tracked for each association is limited to this value This variable is fully dynamic, the new value will be adopted for all newly arriving associations, existing associations are treated as they were previously. Global tracking will decrease the number of collisions within the nat at a cost of increased processing load, memory usage, complexity, and possible nat state problems in complex networks with multiple nats. We recommend not tracking global IP addresses, this will still result in a fully functional nat. net.inet.ip.alias.sctp.up_timer: 300 Timeout value to keep an association up with no traffic. This value cannot be 0. net.inet.ip.dummynet.codel.interval: 100000 Default codel AQM interval in microseconds. The value must be in the range 1..5000000. net.inet.ip.dummynet.codel.target: 5000 Default codel AQM target delay time in microseconds (the minimum acceptable persistent queue delay). The value must be in the range 1..5000000. net.inet.ip.dummynet.expire: 1 Lazily delete dynamic pipes/queue once they have no pending traf- fic. You can disable this by setting the variable to 0, in which case the pipes/queues will only be deleted when the threshold is reached. net.inet.ip.dummynet.fqcodel.flows: 1024 Defines the default total number of flow queues (sub-queues) that fq_codel creates and manages. The value must be in the range 1..65536. net.inet.ip.dummynet.fqcodel.interval: 100000 Default fq_codel scheduler/AQM interval in microseconds. The value must be in the range 1..5000000. net.inet.ip.dummynet.fqcodel.limit: 10240 The default hard size limit (in unit of packet) of all queues managed by an instance of the fq_codel scheduler. The value must be in the range 1..20480. net.inet.ip.dummynet.fqcodel.quantum: 1514 The default quantum (credit) of the fq_codel in unit of byte. The value must be in the range 1..9000. net.inet.ip.dummynet.fqcodel.target: 5000 Default fq_codel scheduler/AQM target delay time in microseconds (the minimum acceptable persistent queue delay). The value must be in the range 1..5000000. net.inet.ip.dummynet.fqpie.alpha: 125 The default alpha parameter (scaled by 1000) for fq_pie sched- uler/AQM. The value must be in the range 1..7000. net.inet.ip.dummynet.fqpie.beta: 1250 The default beta parameter (scaled by 1000) for fq_pie sched- uler/AQM. The value must be in the range 1..7000. net.inet.ip.dummynet.fqpie.flows: 1024 Defines the default total number of flow queues (sub-queues) that fq_pie creates and manages. The value must be in the range 1..65536. net.inet.ip.dummynet.fqpie.limit: 10240 The default hard size limit (in unit of packet) of all queues managed by an instance of the fq_pie scheduler. The value must be in the range 1..20480. net.inet.ip.dummynet.fqpie.max_burst: 150000 The default maximum period of microseconds that fq_pie sched- uler/AQM does not drop/mark packets. The value must be in the range 1..10000000. net.inet.ip.dummynet.fqpie.max_ecnth: 99 The default maximum ECN probability threshold (scaled by 1000) for fq_pie scheduler/AQM. The value must be in the range 1..7000. net.inet.ip.dummynet.fqpie.quantum: 1514 The default quantum (credit) of the fq_pie in unit of byte. The value must be in the range 1..9000. net.inet.ip.dummynet.fqpie.target: 15000 The default target delay of the fq_pie in unit of microsecond. The value must be in the range 1..5000000. net.inet.ip.dummynet.fqpie.tupdate: 15000 The default tupdate of the fq_pie in unit of microsecond. The value must be in the range 1..5000000. net.inet.ip.dummynet.hash_size: 64 Default size of the hash table used for dynamic pipes/queues. This value is used when no buckets option is specified when con- figuring a pipe/queue. net.inet.ip.dummynet.io_fast: 0 If set to a non-zero value, the "fast" mode of dummynet operation (see above) is enabled. net.inet.ip.dummynet.io_pkt Number of packets passed to dummynet. net.inet.ip.dummynet.io_pkt_drop Number of packets dropped by dummynet. net.inet.ip.dummynet.io_pkt_fast Number of packets bypassed by the dummynet scheduler. net.inet.ip.dummynet.max_chain_len: 16 Target value for the maximum number of pipes/queues in a hash bucket. The product max_chain_len*hash_size is used to determine the threshold over which empty pipes/queues will be expired even when net.inet.ip.dummynet.expire=0. net.inet.ip.dummynet.red_lookup_depth: 256 net.inet.ip.dummynet.red_avg_pkt_size: 512 net.inet.ip.dummynet.red_max_pkt_size: 1500 Parameters used in the computations of the drop probability for the RED algorithm. net.inet.ip.dummynet.pie.alpha: 125 The default alpha parameter (scaled by 1000) for pie AQM. The value must be in the range 1..7000. net.inet.ip.dummynet.pie.beta: 1250 The default beta parameter (scaled by 1000) for pie AQM. The value must be in the range 1..7000. net.inet.ip.dummynet.pie.max_burst: 150000 The default maximum period of microseconds that pie AQM does not drop/mark packets. The value must be in the range 1..10000000. net.inet.ip.dummynet.pie.max_ecnth: 99 The default maximum ECN probability threshold (scaled by 1000) for pie AQM. The value must be in the range 1..7000. net.inet.ip.dummynet.pie.target: 15000 The default target delay of pie AQM in unit of microsecond. The value must be in the range 1..5000000. net.inet.ip.dummynet.pie.tupdate: 15000 The default tupdate of pie AQM in unit of microsecond. The value must be in the range 1..5000000. net.inet.ip.dummynet.pipe_byte_limit: 1048576 net.inet.ip.dummynet.pipe_slot_limit: 100 The maximum queue size that can be specified in bytes or packets. These limits prevent accidental exhaustion of resources such as mbufs. If you raise these limits, you should make sure the sys- tem is configured so that sufficient resources are available. net.inet.ip.fw.autoinc_step: 100 Delta between rule numbers when auto-generating them. The value must be in the range 1..1000. net.inet.ip.fw.curr_dyn_buckets: net.inet.ip.fw.dyn_buckets The current number of buckets in the hash table for dynamic rules (readonly). net.inet.ip.fw.debug: 1 Controls debugging messages produced by ipfw. net.inet.ip.fw.default_rule: 65535 The default rule number (read-only). By the design of ipfw, the default rule is the last one, so its number can also serve as the highest number allowed for a rule. net.inet.ip.fw.dyn_buckets: 256 The number of buckets in the hash table for dynamic rules. Must be a power of 2, up to 65536. It only takes effect when all dy- namic rules have expired, so you are advised to use a flush com- mand to make sure that the hash table is resized. net.inet.ip.fw.dyn_count: 3 Current number of dynamic rules (read-only). net.inet.ip.fw.dyn_keepalive: 1 Enables generation of keepalive packets for keep-state rules on TCP sessions. A keepalive is generated to both sides of the con- nection every 5 seconds for the last 20 seconds of the lifetime of the rule. net.inet.ip.fw.dyn_max: 8192 Maximum number of dynamic rules. When you hit this limit, no more dynamic rules can be installed until old ones expire. net.inet.ip.fw.dyn_ack_lifetime: 300 net.inet.ip.fw.dyn_syn_lifetime: 20 net.inet.ip.fw.dyn_fin_lifetime: 1 net.inet.ip.fw.dyn_rst_lifetime: 1 net.inet.ip.fw.dyn_udp_lifetime: 5 net.inet.ip.fw.dyn_short_lifetime: 30 These variables control the lifetime, in seconds, of dynamic rules. Upon the initial SYN exchange the lifetime is kept short, then increased after both SYN have been seen, then decreased again during the final FIN exchange or when a RST is received. Both dyn_fin_lifetime and dyn_rst_lifetime must be strictly lower than 5 seconds, the period of repetition of keepalives. The firewall enforces that. net.inet.ip.fw.dyn_keep_states: 0 Keep dynamic states on rule/set deletion. States are relinked to default rule (65535). This can be handly for ruleset reload. Turned off by default. net.inet.ip.fw.enable: 1 Enables the firewall. Setting this variable to 0 lets you run your machine without firewall even if compiled in. net.inet6.ip6.fw.enable: 1 provides the same functionality as above for the IPv6 case. net.inet.ip.fw.one_pass: 1 When set, the packet exiting from the dummynet pipe or from ng_ipfw(4) node is not passed though the firewall again. Other- wise, after an action, the packet is reinjected into the firewall at the next rule. net.inet.ip.fw.tables_max: 128 Maximum number of tables. net.inet.ip.fw.verbose: 1 Enables verbose messages. net.inet.ip.fw.verbose_limit: 0 Limits the number of messages produced by a verbose firewall. net.inet6.ip6.fw.deny_unknown_exthdrs: 1 If enabled packets with unknown IPv6 Extension Headers will be denied. net.link.ether.ipfw: 0 Controls whether layer2 packets are passed to ipfw. Default is no. net.link.bridge.ipfw: 0 Controls whether bridged packets are passed to ipfw. Default is no. net.inet.ip.fw.nat64_debug: 0 Controls debugging messages produced by ipfw_nat64 module. net.inet.ip.fw.nat64_direct_output: 0 Controls the output method used by ipfw_nat64 module: 0 A packet is handled by ipfw twice. First time an origi- nal packet is handled by ipfw and consumed by ipfw_nat64 translator. Then translated packet is queued via netisr to input processing again. 1 A packet is handled by ipfw only once, and after transla- tion it will be pushed directly to outgoing interface. INTERNAL DIAGNOSTICS There are some commands that may be useful to understand current state of certain subsystems inside kernel module. These commands provide debug- ging output which may change without notice. Currently the following commands are available as internal sub-options: iflist Lists all interface which are currently tracked by ipfw with their in-kernel status. talist List all table lookup algorithms currently available. EXAMPLES There are far too many possible uses of ipfw so this Section will only give a small set of examples. BASIC PACKET FILTERING This command adds an entry which denies all tcp packets from cracker.evil.org to the telnet port of wolf.tambov.su from being for- warded by the host: ipfw add deny tcp from cracker.evil.org to wolf.tambov.su telnet This one disallows any connection from the entire cracker's network to my host: ipfw add deny ip from 123.45.67.0/24 to my.host.org A first and efficient way to limit access (not using dynamic rules) is the use of the following rules: ipfw add allow tcp from any to any established ipfw add allow tcp from net1 portlist1 to net2 portlist2 setup ipfw add allow tcp from net3 portlist3 to net3 portlist3 setup ... ipfw add deny tcp from any to any The first rule will be a quick match for normal TCP packets, but it will not match the initial SYN packet, which will be matched by the setup rules only for selected source/destination pairs. All other SYN packets will be rejected by the final deny rule. If you administer one or more subnets, you can take advantage of the ad- dress sets and or-blocks and write extremely compact rulesets which se- lectively enable services to blocks of clients, as below: goodguys="{ 10.1.2.0/24{20,35,66,18} or 10.2.3.0/28{6,3,11} }" badguys="10.1.2.0/24{8,38,60}" ipfw add allow ip from ${goodguys} to any ipfw add deny ip from ${badguys} to any ... normal policies ... The verrevpath option could be used to do automated anti-spoofing by adding the following to the top of a ruleset: ipfw add deny ip from any to any not verrevpath in This rule drops all incoming packets that appear to be coming to the sys- tem on the wrong interface. For example, a packet with a source address belonging to a host on a protected internal network would be dropped if it tried to enter the system from an external interface. The antispoof option could be used to do similar but more restricted anti-spoofing by adding the following to the top of a ruleset: ipfw add deny ip from any to any not antispoof in This rule drops all incoming packets that appear to be coming from an- other directly connected system but on the wrong interface. For example, a packet with a source address of 192.168.0.0/24, configured on fxp0, but coming in on fxp1 would be dropped. The setdscp option could be used to (re)mark user traffic, by adding the following to the appropriate place in ruleset: ipfw add setdscp be ip from any to any dscp af11,af21 SELECTIVE MIRRORING If your network has network traffic analyzer connected to your host di- rectly via dedicated interface or remotely via RSPAN vlan, you can selec- tively mirror some Ethernet layer2 frames to the analyzer. First, make sure your firewall is already configured and runs. Then, en- able layer2 processing if not already enabled: sysctl net.link.ether.ipfw=1 Next, load needed additional kernel modules: kldload ng_ether ng_ipfw Optionally, make system load these modules automatically at startup: sysrc kld_list+="ng_ether ng_ipfw" Next, configure ng_ipfw(4) kernel module to transmit mirrored copies of layer2 frames out via vlan900 interface: ngctl connect ipfw: vlan900: 1 lower Think of "1" here as of "mirroring instance index" and vlan900 is its destination. You can have arbitrary number of instances. Refer to ng_ipfw(4) for details. At last, actually start mirroring of selected frames using "instance 1". For frames incoming from em0 interface: ipfw add ngtee 1 ip from any to 192.168.0.1 layer2 in recv em0 For frames outgoing to em0 interface: ipfw add ngtee 1 ip from any to 192.168.0.1 layer2 out xmit em0 For both incoming and outgoing frames while flowing through em0: ipfw add ngtee 1 ip from any to 192.168.0.1 layer2 via em0 Make sure you do not perform mirroring for already duplicated frames or kernel may hang as there is no safety net. DYNAMIC RULES In order to protect a site from flood attacks involving fake TCP packets, it is safer to use dynamic rules: ipfw add check-state ipfw add deny tcp from any to any established ipfw add allow tcp from my-net to any setup keep-state This will let the firewall install dynamic rules only for those connec- tion which start with a regular SYN packet coming from the inside of our network. Dynamic rules are checked when encountering the first occur- rence of a check-state, keep-state or limit rule. A check-state rule should usually be placed near the beginning of the ruleset to minimize the amount of work scanning the ruleset. Your mileage may vary. For more complex scenarios with dynamic rules record-state and defer-action can be used to precisely control creation and checking of dynamic rules. Example of usage of these options are provided in NETWORK ADDRESS TRANSLATION (NAT) Section. To limit the number of connections a user can open you can use the fol- lowing type of rules: ipfw add allow tcp from my-net/24 to any setup limit src-addr 10 ipfw add allow tcp from any to me setup limit src-addr 4 The former (assuming it runs on a gateway) will allow each host on a /24 network to open at most 10 TCP connections. The latter can be placed on a server to make sure that a single client does not use more than 4 si- multaneous connections. BEWARE: stateful rules can be subject to denial-of-service attacks by a SYN-flood which opens a huge number of dynamic rules. The effects of such attacks can be partially limited by acting on a set of sysctl(8) variables which control the operation of the firewall. Here is a good usage of the list command to see accounting records and timestamp information: ipfw -at list or in short form without timestamps: ipfw -a list which is equivalent to: ipfw show Next rule diverts all incoming packets from 192.168.2.0/24 to divert port 5000: ipfw divert 5000 ip from 192.168.2.0/24 to any in TRAFFIC SHAPING The following rules show some of the applications of ipfw and dummynet for simulations and the like. This rule drops random incoming packets with a probability of 5%: ipfw add prob 0.05 deny ip from any to any in A similar effect can be achieved making use of dummynet pipes: dnctl add pipe 10 ip from any to any dnctl pipe 10 config plr 0.05 We can use pipes to artificially limit bandwidth, e.g. on a machine act- ing as a router, if we want to limit traffic from local clients on 192.168.2.0/24 we do: ipfw add pipe 1 ip from 192.168.2.0/24 to any out dnctl pipe 1 config bw 300Kbit/s queue 50KBytes note that we use the out modifier so that the rule is not used twice. Remember in fact that ipfw rules are checked both on incoming and outgo- ing packets. Should we want to simulate a bidirectional link with bandwidth limita- tions, the correct way is the following: ipfw add pipe 1 ip from any to any out ipfw add pipe 2 ip from any to any in dnctl pipe 1 config bw 64Kbit/s queue 10Kbytes dnctl pipe 2 config bw 64Kbit/s queue 10Kbytes The above can be very useful, e.g. if you want to see how your fancy Web page will look for a residential user who is connected only through a slow link. You should not use only one pipe for both directions, unless you want to simulate a half-duplex medium (e.g. AppleTalk, Ethernet, IRDA). It is not necessary that both pipes have the same configuration, so we can also simulate asymmetric links. Should we want to verify network performance with the RED queue manage- ment algorithm: ipfw add pipe 1 ip from any to any dnctl pipe 1 config bw 500Kbit/s queue 100 red 0.002/30/80/0.1 Another typical application of the traffic shaper is to introduce some delay in the communication. This can significantly affect applications which do a lot of Remote Procedure Calls, and where the round-trip-time of the connection often becomes a limiting factor much more than band- width: ipfw add pipe 1 ip from any to any out ipfw add pipe 2 ip from any to any in dnctl pipe 1 config delay 250ms bw 1Mbit/s dnctl pipe 2 config delay 250ms bw 1Mbit/s Per-flow queueing can be useful for a variety of purposes. A very simple one is counting traffic: ipfw add pipe 1 tcp from any to any ipfw add pipe 1 udp from any to any ipfw add pipe 1 ip from any to any dnctl pipe 1 config mask all The above set of rules will create queues (and collect statistics) for all traffic. Because the pipes have no limitations, the only effect is collecting statistics. Note that we need 3 rules, not just the last one, because when ipfw tries to match IP packets it will not consider ports, so we would not see connections on separate ports as different ones. A more sophisticated example is limiting the outbound traffic on a net with per-host limits, rather than per-network limits: ipfw add pipe 1 ip from 192.168.2.0/24 to any out ipfw add pipe 2 ip from any to 192.168.2.0/24 in dnctl pipe 1 config mask src-ip 0x000000ff bw 200Kbit/s queue 20Kbytes dnctl pipe 2 config mask dst-ip 0x000000ff bw 200Kbit/s queue 20Kbytes LOOKUP TABLES In the following example, we need to create several traffic bandwidth classes and we need different hosts/networks to fall into different classes. We create one pipe for each class and configure them accord- ingly. Then we create a single table and fill it with IP subnets and ad- dresses. For each subnet/host we set the argument equal to the number of the pipe that it should use. Then we classify traffic using a single rule: dnctl pipe 1 config bw 1000Kbyte/s dnctl pipe 4 config bw 4000Kbyte/s ... ipfw table T1 create type addr ipfw table T1 add 192.168.2.0/24 1 ipfw table T1 add 192.168.0.0/27 4 ipfw table T1 add 192.168.0.2 1 ... ipfw add pipe tablearg ip from 'table(T1)' to any Using the fwd action, the table entries may include hostnames and IP ad- dresses. ipfw table T2 create type addr valtype ipv4 ipfw table T2 add 192.168.2.0/24 10.23.2.1 ipfw table T2 add 192.168.0.0/27 router1.dmz ... ipfw add 100 fwd tablearg ip from any to 'table(T2)' In the following example per-interface firewall is created: ipfw table IN create type iface valtype skipto,fib ipfw table IN add vlan20 12000,12 ipfw table IN add vlan30 13000,13 ipfw table OUT create type iface valtype skipto ipfw table OUT add vlan20 22000 ipfw table OUT add vlan30 23000 .. ipfw add 100 setfib tablearg ip from any to any recv 'table(IN)' in ipfw add 200 skipto tablearg ip from any to any recv 'table(IN)' in ipfw add 300 skipto tablearg ip from any to any xmit 'table(OUT)' out The following example illustrate usage of flow tables: ipfw table fl create type flow:src-ip,proto,dst-ip,dst-port ipfw table fl add 2a02:6b8:77::88,tcp,2a02:6b8:77::99,80 11 ipfw table fl add 10.0.0.1,udp,10.0.0.2,53 12 .. ipfw add 100 allow ip from any to any flow 'table(fl,11)' recv ix0 SETS OF RULES To add a set of rules atomically, e.g. set 18: ipfw set disable 18 ipfw add NN set 18 ... # repeat as needed ipfw set enable 18 To delete a set of rules atomically the command is simply: ipfw delete set 18 To test a ruleset and disable it and regain control if something goes wrong: ipfw set disable 18 ipfw add NN set 18 ... # repeat as needed ipfw set enable 18; echo done; sleep 30 && ipfw set disable 18 Here if everything goes well, you press control-C before the "sleep" ter- minates, and your ruleset will be left active. Otherwise, e.g. if you cannot access your box, the ruleset will be disabled after the sleep ter- minates thus restoring the previous situation. To show rules of the specific set: ipfw set 18 show To show rules of the disabled set: ipfw -S set 18 show To clear a specific rule counters of the specific set: ipfw set 18 zero NN To delete a specific rule of the specific set: ipfw set 18 delete NN NAT, REDIRECT AND LSNAT First redirect all the traffic to nat instance 123: ipfw add nat 123 all from any to any Then to configure nat instance 123 to alias all the outgoing traffic with ip 192.168.0.123, blocking all incoming connections, trying to keep same ports on both sides, clearing aliasing table on address change and keep- ing a log of traffic/link statistics: ipfw nat 123 config ip 192.168.0.123 log deny_in reset same_ports Or to change address of instance 123, aliasing table will be cleared (see reset option): ipfw nat 123 config ip 10.0.0.1 To see configuration of nat instance 123: ipfw nat 123 show config To show logs of all the instances in range 111-999: ipfw nat 111-999 show To see configurations of all instances: ipfw nat show config Or a redirect rule with mixed modes could looks like: ipfw nat 123 config redirect_addr 10.0.0.1 10.0.0.66 redirect_port tcp 192.168.0.1:80 500 redirect_proto udp 192.168.1.43 192.168.1.1 redirect_addr 192.168.0.10,192.168.0.11 10.0.0.100 # LSNAT redirect_port tcp 192.168.0.1:80,192.168.0.10:22 500 # LSNAT or it could be split in: ipfw nat 1 config redirect_addr 10.0.0.1 10.0.0.66 ipfw nat 2 config redirect_port tcp 192.168.0.1:80 500 ipfw nat 3 config redirect_proto udp 192.168.1.43 192.168.1.1 ipfw nat 4 config redirect_addr 192.168.0.10,192.168.0.11,192.168.0.12 10.0.0.100 ipfw nat 5 config redirect_port tcp 192.168.0.1:80,192.168.0.10:22,192.168.0.20:25 500 Sometimes you may want to mix NAT and dynamic rules. It could be achieved with record-state and defer-action options. Problem is, you need to create dynamic rule before NAT and check it after NAT actions (or vice versa) to have consistent addresses and ports. Rule with keep-state option will trigger activation of existing dynamic state, and action of such rule will be performed as soon as rule is matched. In case of NAT and allow rule packet need to be passed to NAT, not allowed as soon is possible. There is example of set of rules to achieve this. Bear in mind that this is example only and it is not very useful by itself. On way out, after all checks place this rules: ipfw add allow record-state skip-action ipfw add nat 1 And on way in there should be something like this: ipfw add nat 1 ipfw add check-state Please note, that first rule on way out doesn't allow packet and doesn't execute existing dynamic rules. All it does, create new dynamic rule with allow action, if it is not created yet. Later, this dynamic rule is used on way in by check-state rule. CONFIGURING CODEL, PIE, FQ-CODEL and FQ-PIE AQM codel and pie AQM can be configured for dummynet pipe or queue. To configure a pipe with codel AQM using default configuration for traf- fic from 192.168.0.0/24 and 1Mbits/s rate limit, we do: dnctl pipe 1 config bw 1mbits/s codel ipfw add 100 pipe 1 ip from 192.168.0.0/24 to any To configure a queue with codel AQM using different configurations param- eters for traffic from 192.168.0.0/24 and 1Mbits/s rate limit, we do: dnctl pipe 1 config bw 1mbits/s dnctl queue 1 config pipe 1 codel target 8ms interval 160ms ecn ipfw add 100 queue 1 ip from 192.168.0.0/24 to any To configure a pipe with pie AQM using default configuration for traffic from 192.168.0.0/24 and 1Mbits/s rate limit, we do: dnctl pipe 1 config bw 1mbits/s pie ipfw add 100 pipe 1 ip from 192.168.0.0/24 to any To configure a queue with pie AQM using different configuration parame- ters for traffic from 192.168.0.0/24 and 1Mbits/s rate limit, we do: dnctl pipe 1 config bw 1mbits/s dnctl queue 1 config pipe 1 pie target 20ms tupdate 30ms ecn ipfw add 100 queue 1 ip from 192.168.0.0/24 to any fq_codel and fq_pie AQM can be configured for dummynet schedulers. To configure fq_codel scheduler using different configurations parameters for traffic from 192.168.0.0/24 and 1Mbits/s rate limit, we do: dnctl pipe 1 config bw 1mbits/s dnctl sched 1 config pipe 1 type fq_codel dnctl queue 1 config sched 1 ipfw add 100 queue 1 ip from 192.168.0.0/24 to any To change fq_codel default configuration for a sched such as disable ECN and change the target to 10ms, we do: dnctl sched 1 config pipe 1 type fq_codel target 10ms noecn Similar to fq_codel, to configure fq_pie scheduler using different con- figurations parameters for traffic from 192.168.0.0/24 and 1Mbits/s rate limit, we do: dnctl pipe 1 config bw 1mbits/s dnctl sched 1 config pipe 1 type fq_pie dnctl queue 1 config sched 1 ipfw add 100 queue 1 ip from 192.168.0.0/24 to any The configurations of fq_pie sched can be changed in a similar way as for fq_codel SEE ALSO cpp(1), m4(1), altq(4), divert(4), dummynet(4), if_bridge(4), ip(4), ipfirewall(4), ng_ether(4), ng_ipfw(4), protocols(5), services(5), init(8), kldload(8), reboot(8), sysctl(8), syslogd(8), sysrc(8) HISTORY The ipfw utility first appeared in FreeBSD 2.0. dummynet was introduced in FreeBSD 2.2.8. Stateful extensions were introduced in FreeBSD 4.0. ipfw2 was introduced in Summer 2002. AUTHORS Ugen J. S. Antsilevich, Poul-Henning Kamp, Alex Nash, Archie Cobbs, Luigi Rizzo, Rasool Al-Saadi. API based upon code written by Daniel Boulet for BSDI. Dummynet has been introduced by Luigi Rizzo in 1997-1998. Some early work (1999-2000) on the dummynet traffic shaper supported by Akamba Corp. The ipfw core (ipfw2) has been completely redesigned and reimplemented by Luigi Rizzo in summer 2002. Further actions and options have been added by various developers over the years. In-kernel NAT support written by Paolo Pisati <piso@FreeBSD.org> as part of a Summer of Code 2005 project. SCTP nat support has been developed by The Centre for Advanced Internet Architectures (CAIA) <http://www.caia.swin.edu.au>. The primary develop- ers and maintainers are David Hayes and Jason But. For further informa- tion visit: <http://www.caia.swin.edu.au/urp/SONATA> Delay profiles have been developed by Alessandro Cerri and Luigi Rizzo, supported by the European Commission within Projects Onelab and Onelab2. CoDel, PIE, FQ-CoDel and FQ-PIE AQM for Dummynet have been implemented by The Centre for Advanced Internet Architectures (CAIA) in 2016, supported by The Comcast Innovation Fund. The primary developer is Rasool Al- Saadi. BUGS The syntax has grown over the years and sometimes it might be confusing. Unfortunately, backward compatibility prevents cleaning up mistakes made in the definition of the syntax. !!! WARNING !!! Misconfiguring the firewall can put your computer in an unusable state, possibly shutting down network services and requiring console access to regain control of it. Incoming packet fragments diverted by divert are reassembled before de- livery to the socket. The action used on those packet is the one from the rule which matches the first fragment of the packet. Packets diverted to userland, and then reinserted by a userland process may lose various packet attributes. The packet source interface name will be preserved if it is shorter than 8 bytes and the userland process saves and reuses the sockaddr_in (as does natd(8)); otherwise, it may be lost. If a packet is reinserted in this manner, later rules may be in- correctly applied, making the order of divert rules in the rule sequence very important. Dummynet drops all packets with IPv6 link-local addresses. Rules using uid or gid may not behave as expected. In particular, incom- ing SYN packets may have no uid or gid associated with them since they do not yet belong to a TCP connection, and the uid/gid associated with a packet may not be as expected if the associated process calls setuid(2) or similar system calls. Rule syntax is subject to the command line environment and some patterns may need to be escaped with the backslash character or quoted appropri- ately. Due to the architecture of libalias(3), ipfw nat is not compatible with the TCP segmentation offloading (TSO). Thus, to reliably nat your net- work traffic, please disable TSO on your NICs using ifconfig(8). ICMP error messages are not implicitly matched by dynamic rules for the respective conversations. To avoid failures of network error detection and path MTU discovery, ICMP error messages may need to be allowed ex- plicitly through static rules. Rules using call and return actions may lead to confusing behaviour if ruleset has mistakes, and/or interaction with other subsystems (netgraph, dummynet, etc.) is used. One possible case for this is packet leaving ipfw in subroutine on the input pass, while later on output encountering unpaired return first. As the call stack is kept intact after input pass, packet will suddenly return to the rule number used on input pass, not on output one. Order of processing should be checked carefully to avoid such mistakes. FreeBSD 13.0 June 4, 2022 FreeBSD 13.0
NAME | SYNOPSIS | DESCRIPTION | PACKET FLOW | SYNTAX | RULE FORMAT | LOOKUP TABLES | SETS OF RULES | STATEFUL FIREWALL | TRAFFIC SHAPER (DUMMYNET) CONFIGURATION | CHECKLIST | FINE POINTS | PACKET DIVERSION | NETWORK ADDRESS TRANSLATION (NAT) | IPv6/IPv4 NETWORK ADDRESS AND PROTOCOL TRANSLATION | IPv6-to-IPv6 NETWORK PREFIX TRANSLATION (NPTv6) | LOADER TUNABLES | SYSCTL VARIABLES | INTERNAL DIAGNOSTICS | EXAMPLES | SEE ALSO | HISTORY | AUTHORS | BUGS
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