SYNOPSIS

In sys/types.h In sys/socket.h In net/route.h

DESCRIPTION

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 In net/route.h header file defines the structures and manifest constants used in this facility.

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

Vt 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 Fn rt_key rt and Fn rt_mask rt macros can be used to extract this information (in the form of a Vt struct sockaddr * ) given a Vt struct rtentry * .

Vt 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).

Vt int rt_flags

See below. If the RTF_UP flag is not present, the Fn rtfree function will delete the route from the radix tree when the last reference drops.

Vt int rt_refcnt

Route entries are reference-counted; this field indicates the number of external (to the radix tree) references.

Vt struct ifnet *rt_ifp

Vt 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.

Vt u_long rt_mtu;

See description of rmx_mtu below.

Vt u_long rt_weight;

See description of rmx_weight below.

Vt u_long rt_expire;

See description of rmx_expire below.

Vt counter64_t rt_pksent;

See description of rmx_pksent below.

Vt 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.

Vt struct mtx rt_mtx

Mutex to lock this routing entry.

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 Er EHOSTUNREACH error from output routines.

RTF_DYNAMIC

This route was created dynamically by Fn rtredirect .

RTF_MODIFIED

This route was modified by Fn rtredirect .

RTF_DONE

Used only in the route(4) protocol, indicating that the request was executed.

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.

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_PROTO1

RTF_PROTO2

RTF_PROTO3

Protocol-specific.

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 address.

RTF_MULTICAST

Indicates that the destination is a multicast address.

Several metrics are supplied in Vt struct rt_metrics passed with routing control messages via route(4) API. Currently only Vt rmx_mtu , rmx_expire , and Vt rmx_pksent metrics are supplied. All others are ignored.

The following metrics are defined by Vt struct rt_metrics :

Vt u_long rmx_locks

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

Vt u_long rmx_mtu

MTU for this path.

Vt u_long rmx_hopcount

Number of intermediate systems on the path to this destination.

Vt 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.

Vt 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 )

Vt u_long rmx_sendpipe

As before, but in the opposite direction.

Vt u_long rmx_ssthresh

The slow-start threshold used in TCP congestion-avoidance.

Vt u_long rmx_rtt

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

Vt u_long rmx_rttvar

The average deviation of the round-trip time to this destination, in units of RMX_RTTUNIT per second.

Vt u_long rmx_pksent

A count of packets successfully sent via this route.

Vt u_long rmx_filler[4]

Empty space available for protocol-specific information.

HISTORY

The Vt rtentry structure first appeared in BSD 4.2 The radix-tree representation of the routing table and the Vt rt_metrics structure first appeared in BSD 4.3 reno

AUTHORS

This manual page was written by An Garrett Wollman .