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NAME    [Toc]    [Back]

     rtentry -- structure of an entry in the kernel routing table

SYNOPSIS    [Toc]    [Back]

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

DESCRIPTION    [Toc]    [Back]

     The kernel provides a common mechanism by which all protocols can store
     and retrieve entries from a central table of routes.  Parts of this mechanism
 are also used to interact with user-level processes by means of a
     socket in the route(4) pseudo-protocol family.  The <net/route.h> header
     file defines the structures and manifest constants used in this facility.

     The basic structure of a route is defined by ``struct rtentry'', which
     includes the following fields:

	   struct radix_node rt_nodes[2];
		   Glue used by the radix-tree routines.  These members also
		   include in their substructure the key (i.e., destination
		   address) and mask used when the route was created.  The
		   rt_key(rt) and rt_mask(rt) macros can be used to extract
		   this information (in the form of a ``struct sockaddr *'')
		   given a struct rtentry *.

	   struct sockaddr *rt_gateway;
		   The ``target'' of the route, which can either represent a
		   destination in its own right (some protocols will put a
		   link-layer address here), or some intermediate stop on the
		   way to that destination (if the RTF_GATEWAY flag is set).

	   long rt_refcnt;
		   Route entries are reference-counted; this field indicates
		   the number of external (to the radix tree) references.  If
		   the RTF_UP flag is not present, the rtfree() function will
		   delete the route from the radix tree when the last reference

	   u_long rt_flags;
		   See below.

	   struct ifnet *rt_ifp;

	   struct ifaddr *rt_ifa;
		   These two fields represent the ``answer'', as it were, to
		   the question posed by a route lookup; that is, they name
		   the interface and interface address to be used in sending a
		   packet to the destination or set of destinations which this
		   route represents.

	   struct sockaddr *rt_genmask;
		   When the rtalloc() family of functions performs a cloning
		   operation as requested by the RTF_CLONING or RTF_PRCLONING
		   flag, this field is used as the mask for the new route
		   which is inserted into the table.  If this field is a null
		   pointer, then a host route is generated.

	   caddr_t rt_llinfo;
		   When the RTF_LLINFO flag is set, this field contains information
 specific to the link layer represented by the named
		   interface address.  (It is normally managed by the
		   rt_ifa->ifa_rtrequest() routine.)  Protocols such as arp(4)
		   use this field to reference per-destination state internal
		   to that protocol.

	   struct rt_metrics rt_rmx;
		   See below.

	   struct rtentry *rt_gwroute;
		   This member is a reference to a route whose destination is
		   rt_gateway.	It is only used for RTF_GATEWAY routes.

	   struct rtentry *rt_parent;
		   A reference to the route from which this route was cloned,
		   or a null pointer if this route was not generated by
		   cloning.  See also the RTF_WASCLONED flag.

     The following flag bits are defined:
	   RTF_UP	    The route is not deleted.
	   RTF_GATEWAY	    The route points to an intermediate destination
			    and not the ultimate recipient; the rt_gateway and
			    rt_gwroute fields name that destination.
	   RTF_HOST	    This is a host route.
	   RTF_REJECT	    The destination is presently unreachable.  This
			    should result in an EHOSTUNREACH error from output
	   RTF_DYNAMIC	    This route was created dynamically by
	   RTF_MODIFIED     This route was modified by rtredirect().
	   RTF_DONE	    Used only in the route(4) protocol, indicating
			    that the request was executed.
	   RTF_CLONING	    When this route is returned as a result of a
			    lookup, automatically create a new route using
			    this one as a template and rt_genmask (if present)
			    as a mask.
	   RTF_XRESOLVE     When this route is returned as a result of a
			    lookup, send a report on the route(4) interface
			    requesting that an external process perform resolution
 for this route.  (Used in conjunction with
	   RTF_LLINFO	    Indicates that this route represents information
			    being managed by a link layer's adaptation layer
			    (e.g., ARP).
	   RTF_STATIC	    Indicates that this route was manually added by
			    means of the route(8) command.
	   RTF_BLACKHOLE    Requests that output sent via this route be discarded.

	   RTF_PROTO3	    Protocol-specific.
	   RTF_PRCLONING    Like RTF_CLONING, only managed by an entire protocol.
  (E.g., IP uses this flag to manage a perhost
 cache integrated with the routing table, for
			    those destinations which do not have a link layer
			    performing this function.)
	   RTF_WASCLONED    Indicates that this route was generated as a
			    result of cloning requested by the RTF_CLONING or
			    RTF_PRCLONING flag.  When set, the rt_parent field
			    indicates the route from which this one was generated.

	   RTF_PINNED	    (Reserved for future use to indicate routes which
			    are not to be modified by a routing protocol.)
	   RTF_LOCAL	    Indicates that the destination of this route is an
			    address configured as belonging to this system.
	   RTF_BROADCAST    Indicates that the destination is a broadcast
	   RTF_MULTICAST    Indicates that the destination is a multicast

     Every route has associated with it a set of metrics, defined by struct

	   u_long rmx_locks;
		   Flag bits indicating which metrics the kernel is not permitted
 to dynamically modify.

	   u_long rmx_mtu;
		   MTU for this path.

	   u_long rmx_hopcount;
		   Number of intermediate systems on the path to this destination.

	   u_long rmx_expire;
		   The time (a la time(3)) at which this route should expire,
		   or zero if it should never expire.  It is the responsibility
 of individual protocol suites to ensure that routes are
		   actually deleted once they expire.

	   u_long rmx_recvpipe;
		   Nominally, the bandwidth-delay product for the path from
		   the destination to this system.  In practice, this value is
		   used to set the size of the receive buffer (and thus the
		   window in sliding-window protocols like TCP).

	   u_long rmx_sendpipe;
		   As before, but in the opposite direction.

	   u_long rmx_ssthresh;
		   The slow-start threshold used in TCP congestion-avoidance.

	   u_long rmx_rtt;
		   The round-trip time to this destination, in units of
		   RMX_RTTUNIT per second.

	   u_long rmx_rttvar;
		   The average deviation of the round-type time to this destination,
 in units of RMX_RTTUNIT per second.

	   u_long rmx_pksent;
		   A count of packets successfully sent via this route.

	   u_long rmx_filler[4];
		   Empty space available for protocol-specific information.

SEE ALSO    [Toc]    [Back]

     route(4), route(8), rtalloc(9)

HISTORY    [Toc]    [Back]

     The rtentry structure first appeared in 4.2BSD.  The radix-tree representation
 of the routing table and the rt_metrics structure first appeared
     in 4.3BSD-Reno.  The RTF_PRCLONING mechanism first appeared in
     FreeBSD 2.0.

BUGS    [Toc]    [Back]

     There are a number of historical relics remaining in this interface.  The
     rt_gateway and rmx_filler fields could be named better.

     There is some disagreement over whether it is legitimate for RTF_LLINFO
     to be set by any process other than rt_ifa->ifa_rtrequest().

AUTHORS    [Toc]    [Back]

     This manual page was written by Garrett Wollman.

FreeBSD 5.2.1			October 8, 1996 		 FreeBSD 5.2.1
[ Back ]
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