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ROUTE(4)	       FreeBSD Kernel Interfaces Manual		      ROUTE(4)

     route -- kernel packet forwarding database

     #include <sys/socket.h>
     #include <net/if.h>
     #include <net/route.h>

     socket(PF_ROUTE, SOCK_RAW,	int family);

     UNIX provides some	packet routing facilities.  The	kernel maintains a
     routing information database, which is used in selecting the appropriate
     network interface when transmitting packets.

     A user process (or	possibly multiple co-operating processes) maintains
     this database by sending messages over a special kind of socket.  This
     supplants fixed size ioctl(2)'s used in earlier releases.	Routing	table
     changes may only be carried out by	the super user.

     The operating system may spontaneously emit routing messages in response
     to	external events, such as receipt of a redirect,	or failure to locate a
     suitable route for	a request.  The	message	types are described in greater
     detail below.

     Routing database entries come in two flavors: for a specific host,	or for
     all hosts on a generic subnetwork (as specified by	a bit mask and value
     under the mask.  The effect of wildcard or	default	route may be achieved
     by	using a	mask of	all zeros, and there may be hierarchical routes.

     When the system is	booted and addresses are assigned to the network in-
     terfaces, each protocol family installs a routing table entry for each
     interface when it is ready	for traffic.  Normally the protocol specifies
     the route through each interface as a "direct" connection to the destina-
     tion host or network.  If the route is direct, the	transport layer	of a
     protocol family usually requests the packet be sent to the	same host
     specified in the packet.  Otherwise, the interface	is requested to	ad-
     dress the packet to the gateway listed in the routing entry (i.e. the
     packet is forwarded).

     When routing a packet, the	kernel will attempt to find the	most specific
     route matching the	destination.  (If there	are two	different mask and
     value-under-the-mask pairs	that match, the	more specific is the one with
     more bits in the mask.  A route to	a host is regarded as being supplied
     with a mask of as many ones as there are bits in the destination).	 If no
     entry is found, the destination is	declared to be unreachable, and	a
     routing-miss message is generated if there	are any	listeners on the rout-
     ing control socket	described below.

     A wildcard	routing	entry is specified with	a zero destination address
     value, and	a mask of all zeroes.  Wildcard	routes will be used when the
     system fails to find other	routes matching	the destination.  The combina-
     tion of wildcard routes and routing redirects can provide an economical
     mechanism for routing traffic.

     One opens the channel for passing routing control messages	by using the
     socket call shown in the synopsis above:

     The family	parameter may be AF_UNSPEC which will provide routing informa-
     tion for all address families, or can be restricted to a specific address
     family by specifying which	one is desired.	 There can be more than	one
     routing socket open per system.

     Messages are formed by a header followed by a small number	of sockaddrs
     (now variable length particularly in the ISO case), interpreted by	posi-
     tion, and delimited by the	new length entry in the	sockaddr.  An example
     of	a message with four addresses might be an ISO redirect:	Destination,
     Netmask, Gateway, and Author of the redirect.  The	interpretation of
     which address are present is given	by a bit mask within the header, and
     the sequence is least significant to most significant bit within the vec-

     Any messages sent to the kernel are returned, and copies are sent to all
     interested	listeners.  The	exception to this is a new address marked as
     tentative,	where copies will be sent once Duplicate Address Detection has
     completed and the tentative flag cleared or the duplicated	flag set.
     Also, new address messages	will also be emitted when other	flags on the
     address change such as deprecated and detached.  The kernel will provide
     the process ID for	the sender, and	the sender may use an additional se-
     quence field to distinguish between outstanding messages.	However, mes-
     sage replies may be lost when kernel buffers are exhausted.

     The kernel	may reject certain messages, and will indicate this by filling
     in	the rtm_errno field.  The routing code returns EEXIST if requested to
     duplicate an existing entry, ESRCH	if requested to	delete a non-existent
     entry, or ENOBUFS if insufficient resources were available	to install a
     new route.	 In the	current	implementation,	all routing processes run lo-
     cally, and	the values for rtm_errno are available through the normal
     errno mechanism, even if the routing reply	message	is lost.

     A process may avoid the expense of	reading	replies	to its own messages by
     issuing a setsockopt(2) call indicating that the SO_USELOOPBACK option at
     the SOL_SOCKET level is to	be turned off.	A process may ignore all mes-
     sages from	the routing socket by doing a shutdown(2) system call for fur-
     ther input.

     A process can specify which route message types it's interested in	by
     passing an	array of route messsage	types to the setsockopt(2) call	with
     the RO_MSGFILTER option at	the PF_ROUTE level.  For example, to only get
     specific messages:

	   unsigned char rtfilter[] = {	RTM_IFINFO, RTM_IFANNOUNCE };

	   if (setsockopt(routefd, PF_ROUTE, RO_MSGFILTER,
	       &rtfilter, (socklen_t)sizeof(rtfilter)) == -1)
		   err(1, "setsockopt(RO_MSGFILTER)");

     If	a route	is in use when it is deleted, the routing entry	will be	marked
     down and removed from the routing table, but the resources	associated
     with it will not be reclaimed until all references	to it are released.
     User processes can	obtain information about the routing entry to a	spe-
     cific destination by using	a RTM_GET message, or by reading the /dev/kmem
     device, or	by calling sysctl(3).

     The messages are:

     #define RTM_ADD	     0x1    /* Add Route */
     #define RTM_DELETE	     0x2    /* Delete Route */
     #define RTM_CHANGE	     0x3    /* Change Metrics, Flags, or Gateway */
     #define RTM_GET	     0x4    /* Report Information */
     #define RTM_LOSING	     0x5    /* Kernel Suspects Partitioning */
     #define RTM_REDIRECT    0x6    /* Told to use different route */
     #define RTM_MISS	     0x7    /* Lookup failed on	this address */
     #define RTM_LOCK	     0x8     /*	fix specified metrics */
     #define RTM_OLDADD	     0x9     /*	caused by SIOCADDRT */
     #define RTM_OLDDEL	     0xa     /*	caused by SIOCDELRT */
     #define RTM_ONEWADDR    0xc    /* Old (pre-8.0) RTM_NEWADDR message */
     //	#define	RTM_RESOLVE  0xb     /*	req to resolve dst to LL addr */
     #define RTM_ODELADDR    0xd    /* Old (pre-8.0) RTM_DELADDR message */
     #define RTM_OOIFINFO    0xe    /* Old (pre-1.5) RTM_IFINFO	message	*/
     #define RTM_OIFINFO     0xf    /* Old (pre-6.0) RTM_IFINFO	message	*/
     #define RTM_IFANNOUNCE  0x10   /* iface arrival/departure */
     #define RTM_IEEE80211   0x11    /*	IEEE80211 wireless event */
     #define RTM_SETGATE     0x12    /*	set prototype gateway for clones
				      *	(see example in	arp_rtrequest).
     #define RTM_LLINFO_UPD  0x13    /*	indication to ARP/NDP/etc. that	link-layer
				      *	address	has changed
     #define RTM_IFINFO	     0x14   /* iface/link going	up/down	etc. */
     #define RTM_OCHGADDR    0x15   /* Old (pre-8.0) RTM_CHGADDR message */
     #define RTM_NEWADDR     0x16   /* address being added to iface */
     #define RTM_DELADDR     0x17   /* address being removed from iface	*/
     #define RTM_CHGADDR     0x18   /* address properties changed */

     A message header consists of one of the following:

     struct rt_msghdr {
	 u_short rtm_msglen;	    /* to skip over non-understood messages */
	 u_char	 rtm_version;	    /* future binary compatibility */
	 u_char	 rtm_type;	    /* message type */
	 u_short rtm_index;	    /* index for associated ifp	*/
	 int	 rtm_flags;	    /* flags, incl kern	& message, e.g.	DONE */
	 int	 rtm_addrs;	    /* bitmask identifying sockaddrs in	msg */
	 pid_t	 rtm_pid;	    /* identify	sender */
	 int	 rtm_seq;	    /* for sender to identify action */
	 int	 rtm_errno;	    /* why failed */
	 int	 rtm_use;	    /* from rtentry */
	 u_long	 rtm_inits;	    /* which metrics we	are initializing */
	 struct	 rt_metrics rtm_rmx; /*	metrics	themselves */

     struct if_msghdr {
	 u_short ifm_msglen;	    /* to skip over non-understood messages */
	 u_char	 ifm_version;	    /* future binary compatibility */
	 u_char	 ifm_type;	    /* message type */
	 int	 ifm_addrs;	    /* like rtm_addrs */
	 int	 ifm_flags;	    /* value of	if_flags */
	 u_short ifm_index;	    /* index for associated ifp	*/
	 struct	 if_data ifm_data;  /* statistics and other data about if */

     struct ifa_msghdr {
	 u_short ifam_msglen;	    /* to skip over non-understood messages */
	 u_char	 ifam_version;	    /* future binary compatibility */
	 u_char	 ifam_type;	    /* message type */
	 u_short ifam_index;	    /* index for associated ifp	*/
	 int	 ifam_flags;	    /* value of	ifa_flags */
	 int	 ifam_addrs;	    /* like rtm_addrs */
	 pid_t	 ifam_pid;	    /* identify	sender */
	 int	 ifam_addrflags;    /* family specific address flags */
	 int	 ifam_metric;	    /* value of	ifa_metric */

     struct if_announcemsghdr {
	 u_short ifan_msglen;	    /* to skip over non-understood messages */
	 u_char	 ifan_version;	    /* future binary compatibility */
	 u_char	 ifan_type;	    /* message type */
	 u_short ifan_index;	    /* index for associated ifp	*/
	 char	 ifan_name[IFNAMSIZ]; /* if name, e.g. "en0" */
	 u_short ifan_what;	    /* what type of announcement */

     The RTM_IFINFO message uses a if_msghdr header, the RTM_NEWADDR,
     RTM_CHGADDR, and RTM_DELADDR messages use a ifa_msghdr header, the
     RTM_IFANNOUNCE message uses a if_announcemsghdr header, and all other
     messages use the rt_msghdr	header.

     The metrics structure is:

     struct rt_metrics {
	 u_long	rmx_locks;	    /* Kernel must leave these values alone */
	 u_long	rmx_mtu;	    /* MTU for this path */
	 u_long	rmx_hopcount;	    /* max hops	expected */
	 u_long	rmx_expire;	    /* lifetime	for route, e.g.	redirect */
	 u_long	rmx_recvpipe;	    /* inbound delay-bandwidth product */
	 u_long	rmx_sendpipe;	    /* outbound	delay-bandwidth	product	*/
	 u_long	rmx_ssthresh;	    /* outbound	gateway	buffer limit */
	 u_long	rmx_rtt;	    /* estimated round trip time */
	 u_long	rmx_rttvar;	    /* estimated rtt variance */
	 u_long	rmx_pksent;	    /* packets sent using this route */

     Flags include the values:

     #define RTF_UP	   0x1	     /*	route usable */
     #define RTF_GATEWAY   0x2	     /*	destination is a gateway */
     #define RTF_HOST	   0x4	     /*	host entry (net	otherwise) */
     #define RTF_REJECT	   0x8	     /*	host or	net unreachable	*/
     #define RTF_DYNAMIC   0x10	     /*	created	dynamically (by	redirect) */
     #define RTF_MODIFIED  0x20	     /*	modified dynamically (by redirect) */
     #define RTF_DONE	   0x40	     /*	message	confirmed */
     #define RTF_MASK	   0x80	     /*	subnet mask present */
     #define RTF_CONNECTED 0x100     /*	hosts on this route are	neighbours */
     #define RTF_LLDATA	   0x400     /*	used by	apps to	add/del	L2 entries */
     #define RTF_STATIC	   0x800     /*	manually added */
     #define RTF_BLACKHOLE 0x1000    /*	just discard pkts (during updates) */
     #define RTF_PROTO2	   0x4000    /*	protocol specific routing flag */
     #define RTF_PROTO1	   0x8000    /*	protocol specific routing flag */
     #define RTF_SRC	   0x10000   /*	route has fixed	source address */
     #define RTF_ANNOUNCE  0x20000   /*	announce new ARP or NDP	entry */
     #define RTF_LOCAL	   0x40000   /*	route represents a local address */
     #define RTF_BROADCAST 0x80000   /*	route represents a bcast address */

     Specifiers	for metric values in rmx_locks and rtm_inits are:

     #define RTV_MTU	   0x1	  /* init or lock _mtu */
     #define RTV_HOPCOUNT  0x2	  /* init or lock _hopcount */
     #define RTV_EXPIRE	   0x4	  /* init or lock _expire */
     #define RTV_RPIPE	   0x8	  /* init or lock _recvpipe */
     #define RTV_SPIPE	   0x10	  /* init or lock _sendpipe */
     #define RTV_SSTHRESH  0x20	  /* init or lock _ssthresh */
     #define RTV_RTT	   0x40	  /* init or lock _rtt */
     #define RTV_RTTVAR	   0x80	  /* init or lock _rttvar */

     Specifiers	for which addresses are	present	in the messages	are:

     #define RTA_DST	   0x1	  /* destination sockaddr present */
     #define RTA_GATEWAY   0x2	  /* gateway sockaddr present */
     #define RTA_NETMASK   0x4	  /* netmask sockaddr present */
     #define RTA_GENMASK   0x8	  /* cloning mask sockaddr present */
     #define RTA_IFP	   0x10	  /* interface name sockaddr present */
     #define RTA_IFA	   0x20	  /* interface addr sockaddr present */
     #define RTA_AUTHOR	   0x40	  /* sockaddr for author of redirect */
     #define RTA_BRD	   0x80	  /* for NEWADDR, broadcast or p-p dest	addr */
     #define RTA_TAG	   0x100  /* route tag */

     Flags for IPv6 addresses:

     #define IN6_IFF_ANYCAST	     0x01    /*	anycast	address	*/
     #define IN6_IFF_TENTATIVE	     0x02    /*	tentative address */
     #define IN6_IFF_DUPLICATED	     0x04    /*	DAD detected duplicate */
     #define IN6_IFF_DETACHED	     0x08    /*	may be detached	from the link */
     #define IN6_IFF_DEPRECATED	     0x10    /*	deprecated address */
     #define IN6_IFF_NODAD	     0x20    /*	don't perform DAD on this address
					      *	(used only at first SIOC* call)
     #define IN6_IFF_AUTOCONF	     0x40    /*	autoconfigurable address. */
     #define IN6_IFF_TEMPORARY	     0x80    /*	temporary (anonymous) address. */

     socket(2),	sysctl(3)

     RTM_RESOLVE were obsolete.	 RTF_CONNECTED and RTF_LLDATA appeared in
     NetBSD 8.0.

     ifa_msghdr	gained the fields ifam_pid and ifam_addrflags in NetBSD	8.0.

FreeBSD	13.0			 July 11, 2018			  FreeBSD 13.0


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