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RTENTRY(9) FreeBSD Kernel Developer's Manual RTENTRY(9)
NAME rtentry - structure of an entry in the kernel routing table
SYNOPSIS #include <sys/types.h> #include <sys/socket.h> #include <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 <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).
int rt_flags; See below. If the RTF_UP flag is not present, the rtfree() function will delete the route from the radix tree when the last reference drops.
int rt_refcnt; Route entries are reference-counted; this field indicates the number of external (to the radix tree) references.
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.
u_long rt_mtu; See description of rmx_mtu below.
u_long rt_weight; See description of rmx_weight below.
This member is a reference to a route whose destination is rt_gateway. It is only used for RTF_GATEWAY routes.
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 EHOSTUNREACH error from output routines. RTF_DYNAMIC This route was created dynamically by rtredirect(). RTF_MODIFIED This route was modified by 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 Indicates that this route is immutable to 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 struct rt_metrics passed with routing control messages via route(4) API. Currently only rmx_mtu, rmx_expire, and rmx_pksent metrics are supplied. All others are ignored.
The following metrics are defined by struct rt_metrics:
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 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-trip 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 route(4), route(8),
HISTORY 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.
AUTHORS This manual page was written by Garrett Wollman.
BUGS There are a number of historical relics remaining in this interface. The rt_gateway and rmx_filler fields could be named better.
FreeBSD 14.0-RELEASE-p11 March 5, 2014 FreeBSD 14.0-RELEASE-p11