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ROUTE(7P)							     ROUTE(7P)

NAME    [Toc]    [Back]

     route - kernel packet forwarding database

SYNOPSIS    [Toc]    [Back]

     #include <sys/socket.h>
     #include <net/if.h>
     #include <net/route.h>
     int socket(PF_ROUTE, SOCK_RAW, family);

DESCRIPTION    [Toc]    [Back]

     The system	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 re-direct, 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
     interfaces, 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
     destination 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
     address 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	listers	on the routing
     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
     combination of wildcard routes and	routing	redirects can provide an

									Page 1

ROUTE(7P)							     ROUTE(7P)

     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
     information 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
     interpreted by position.  An example of a message with three addresses
     might be a	redirect:  Destination,	Gateway, and Author of the redirect.
     The interpretation	of which addresses are present is given	by a bit mask
     within the	header,	and the	sequence is least significant to most
     significant bit within the	vector.

     Any messages sent to the kernel are returned, and copies are sent to all
     interested	listeners.  The	kernel will provide the	process	id. for	the
     sender, and the sender may	use an additional sequence field to
     distinguish between outstanding messages.	However, message 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
     locally, 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
     messages from the routing socket by doing a shutdown(2) system call for
     further input.

     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
     specific destination by using a RTM_GET message, or by reading the
     /dev/kmem device.

     Messages include:

	  #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_LOOSING	   0x5	  /* Kernel Suspects Partitioning */
	  #define   RTM_REDIRECT   0x6	  /* Told to use different route */

									Page 2

ROUTE(7P)							     ROUTE(7P)

	  #define   RTM_MISS	   0x7	  /* Lookup failed on this address */
	  #define   RTM_RESOLVE	   0xb	  /* request to	resolve	dst to LL addr */

     A message header consists of:

	  struct rt_msghdr {
	      u_short rmt_msglen;  /* to skip over non-understood messages */
	      u_char  rtm_version; /* future binary compatibility */
	      u_char  rtm_type;	   /* message type */
	      u_short rmt_index;   /* index for	associated ifp */
	      pid_t   rmt_pid;	   /* identify sender */
	      __uint32_t     rtm_addrs;	  /* bitmask identifying sockaddrs in msg */
	      int     rtm_seq;	   /* for sender to identify action */
	      int     rtm_errno;   /* why failed */
	      int     rtm_flags;   /* flags, incl kern & message, e.g. DONE */
	      int     rtm_use;	   /* from rtentry */
	      u_long  rtm_inits;   /* which values we are initializing */
	      struct  rt_metrics rtm_rmx;    /*	metrics	themselves */


	  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 */

     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_CLONING	  0x100	    /* generate	new routes on use */
	  #define   RTF_XRESOLVE  0x200	    /* external	daemon resolves	name */
	  #define   RTF_LLINFO	  0x400	    /* generated by ARP	or ESIS	*/
	  #define   RTF_STATIC	  0x800	    /* manually	added */
	  #define   RTF_BLACKHOLE 0x1000    /* just discard pkts (during updates) */

									Page 3

ROUTE(7P)							     ROUTE(7P)

	  #define   RTF_PROTO2	  0x4000    /* protocol	specific routing flag #1 */
	  #define   RTF_PROTO1	  0x8000    /* protocol	specific routing flag #2 */
	  #define   RTF_CKSUM	  0x10000   /* TCP/UDP checksumming done on this route */

     Specifiers	for metric values in rmx_locks and rtm_inits are:

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

     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 */

SEE ALSO    [Toc]    [Back]

     ip(7p), netintro(7p)

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