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INET(4) BSD Kernel Interfaces Manual INET(4) NAME inet -- Internet protocol family SYNOPSIS #include <sys/types.h> #include <netinet/in.h> DESCRIPTION The Internet protocol family is a collection of protocols layered atop the Internet Protocol (IP) transport layer, and utilizing the Internet address format. The Internet family provides protocol support for the SOCK_STREAM, SOCK_DGRAM, and SOCK_RAW socket types; the SOCK_RAW inter- face provides access to the IP protocol. ADDRESSING Internet addresses are four byte quantities, stored in network standard format (on little endian machines, such as the alpha, amd64 and i386 these are word and byte reversed). The include file <netinet/in.h> de- fines this address as a discriminated union. Sockets bound to the Internet protocol family utilize the following ad- dressing structure, struct sockaddr_in { uint8_t sin_len; sa_family_t sin_family; in_port_t sin_port; struct in_addr sin_addr; char sin_zero[8]; }; Sockets may be created with the local address INADDR_ANY to affect "wildcard" matching on incoming messages. The address in a connect(2) or sendto(2) call may be given as INADDR_ANY to mean "this host". The dis- tinguished address INADDR_BROADCAST is allowed as a shorthand for the broadcast address on the primary network if the first network configured supports broadcast. PROTOCOLS The Internet protocol family is comprised of the IP network protocol, In- ternet Control Message Protocol (ICMP), Internet Group Management Proto- col (IGMP), Transmission Control Protocol (TCP), and User Datagram Proto- col (UDP). TCP is used to support the SOCK_STREAM abstraction while UDP is used to support the SOCK_DGRAM abstraction. A raw interface to IP is available by creating an Internet socket of type SOCK_RAW. The ICMP mes- sage protocol is accessible from a raw socket. The inet address on an interface consist of the address itself, the net- mask, either broadcast address in case of a broadcast interface or peers address in case of point-to-point interface. The following ioctl(2) com- mands are provided for a datagram socket in the Internet domain: SIOCAIFADDR Add address to an interface. The command requires struct in_aliasreq as argument. SIOCDIFADDR Delete address from an interface. The command re- quires struct ifreq as argument. SIOCGIFADDR SIOCGIFBRDADDR SIOCGIFDSTADDR SIOCGIFNETMASK Return address information from interface. The re- turned value is in struct ifreq. This way of ad- dress information retrieval is obsoleted, a pre- ferred way is to use getifaddrs(3) API. MIB Variables A number of variables are implemented in the net.inet branch of the sysctl(3) MIB. In addition to the variables supported by the transport protocols (for which the respective manual pages may be consulted), the following general variables are defined: IPCTL_FORWARDING (ip.forwarding) Boolean: enable/disable forward- ing of IP packets. Defaults to off. IPCTL_SENDREDIRECTS (ip.redirect) Boolean: enable/disable sending of ICMP redirects in response to IP packets for which a better, and for the sender directly reachable, route and next hop is known. De- faults to on. IPCTL_DEFTTL (ip.ttl) Integer: default time-to-live ("TTL") to use for outgoing IP packets. IPCTL_ACCEPTSOURCEROUTE (ip.accept_sourceroute) Boolean: enable/disable accepting of source-routed IP packets (default false). IPCTL_SOURCEROUTE (ip.sourceroute) Boolean: enable/disable for- warding of source-routed IP packets (default false). ip.process_options Integer: control IP options processing. By set- ting this variable to 0, all IP options in the incoming packets will be ignored, and the pack- ets will be passed unmodified. By setting to 1, IP options in the incoming packets will be pro- cessed accordingly. By setting to 2, an ICMP "prohibited by filter" message will be sent back in response to incoming packets with IP options. Default is 1. This sysctl(8) variable affects packets destined for a local host as well as packets forwarded to some other host. ip.rfc6864 Boolean: control IP IDs generation behaviour. True value enables RFC6864 support, which speci- fies that IP ID field of atomic datagrams can be set to any value. The FreeBSD implementation sets it to zero. Enabled by default. ip.random_id Boolean: control IP IDs generation behaviour. Setting this sysctl(8) to 1 causes the ID field in non-atomic IP datagrams (or all IP datagrams, if ip.rfc6864 is disabled) to be randomized in- stead of incremented by 1 with each packet gen- erated. This closes a minor information leak which allows remote observers to determine the rate of packet generation on the machine by watching the counter. At the same time, on high-speed links, it can decrease the ID reuse cycle greatly. Default is 0 (sequential IP IDs). IPv6 flow IDs and fragment IDs are always random. ip.maxfragpackets Integer: maximum number of fragmented packets the host will accept and hold in the reassem- bling queue simultaneously. 0 means that the host will not accept any fragmented packets. -1 means that the host will accept as many frag- mented packets as it receives. ip.maxfragsperpacket Integer: maximum number of fragments the host will accept and hold in the reassembling queue for a packet. 0 means that the host will not accept any fragmented packets. SEE ALSO ioctl(2), socket(2), getifaddrs(3), sysctl(3), icmp(4), intro(4), ip(4), ipfirewall(4), route(4), tcp(4), udp(4), pfil(9) "An Introductory 4.3 BSD Interprocess Communication Tutorial", PS1, 7. "An Advanced 4.3 BSD Interprocess Communication Tutorial", PS1, 8. HISTORY The inet protocol interface appeared in 4.2BSD. The "protocol cloning" code appeared in FreeBSD 2.1. CAVEATS The Internet protocol support is subject to change as the Internet proto- cols develop. Users should not depend on details of the current imple- mentation, but rather the services exported. BSD Feb 4, 2016 BSD
NAME | SYNOPSIS | DESCRIPTION | ADDRESSING | PROTOCOLS | SEE ALSO | HISTORY | CAVEATS
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