6e6b3f7cbc
1. separating L2 tables (ARP, NDP) from the L3 routing tables
2. removing as much locking dependencies among these layers as
possible to allow for some parallelism in the search operations
3. simplify the logic in the routing code,
The most notable end result is the obsolescent of the route
cloning (RTF_CLONING) concept, which translated into code reduction
in both IPv4 ARP and IPv6 NDP related modules, and size reduction in
struct rtentry{}. The change in design obsoletes the semantics of
RTF_CLONING, RTF_WASCLONE and RTF_LLINFO routing flags. The userland
applications such as "arp" and "ndp" have been modified to reflect
those changes. The output from "netstat -r" shows only the routing
entries.
Quite a few developers have contributed to this project in the
past: Glebius Smirnoff, Luigi Rizzo, Alessandro Cerri, and
Andre Oppermann. And most recently:
- Kip Macy revised the locking code completely, thus completing
the last piece of the puzzle, Kip has also been conducting
active functional testing
- Sam Leffler has helped me improving/refactoring the code, and
provided valuable reviews
- Julian Elischer setup the perforce tree for me and has helped
me maintaining that branch before the svn conversion
332 lines
12 KiB
Groff
332 lines
12 KiB
Groff
.\" Copyright (c) 1990, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the University of
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.\" California, Berkeley and its contributors.
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.\" 4. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" From: @(#)route.4 8.6 (Berkeley) 4/19/94
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.\" $FreeBSD$
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.\"
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.Dd November 4, 2004
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.Dt ROUTE 4
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.Os
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.Sh NAME
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.Nm route
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.Nd kernel packet forwarding database
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.Sh SYNOPSIS
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.In sys/types.h
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.In sys/time.h
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.In sys/socket.h
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.In net/if.h
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.In net/route.h
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.Ft int
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.Fn socket PF_ROUTE SOCK_RAW "int family"
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.Sh DESCRIPTION
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.Fx
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provides some packet routing facilities.
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The kernel maintains a routing information database, which
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is used in selecting the appropriate network interface when
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transmitting packets.
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.Pp
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A user process (or possibly multiple co-operating processes)
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maintains this database by sending messages over a special kind
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of socket.
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This supplants fixed size
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.Xr ioctl 2 Ns 's
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used in earlier releases.
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Routing table changes may only be carried out by the super user.
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.Pp
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The operating system may spontaneously emit routing messages in response
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to external events, such as receipt of a re-direct, or failure to
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locate a suitable route for a request.
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The message types are described in greater detail below.
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.Pp
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Routing database entries come in two flavors: for a specific
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host, or for all hosts on a generic subnetwork (as specified
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by a bit mask and value under the mask.
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The effect of wildcard or default route may be achieved by using
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a mask of all zeros, and there may be hierarchical routes.
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.Pp
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When the system is booted and addresses are assigned
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to the network interfaces, each protocol family
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installs a routing table entry for each interface when it is ready for traffic.
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Normally the protocol specifies the route
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through each interface as a
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.Dq direct
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connection to the destination host
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or network.
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If the route is direct, the transport layer of
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a protocol family usually requests the packet be sent to the
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same host specified in the packet.
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Otherwise, the interface
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is requested to address the packet to the gateway listed in the routing entry
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(i.e., the packet is forwarded).
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.Pp
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When routing a packet,
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the kernel will attempt to find
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the most specific route matching the destination.
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(If there are two different mask and value-under-the-mask pairs
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that match, the more specific is the one with more bits in the mask.
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A route to a host is regarded as being supplied with a mask of
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as many ones as there are bits in the destination).
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If no entry is found, the destination is declared to be unreachable,
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and a routing-miss message is generated if there are any
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listeners on the routing control socket described below.
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.Pp
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A wildcard routing entry is specified with a zero
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destination address value, and a mask of all zeroes.
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Wildcard routes will be used
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when the system fails to find other routes matching the
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destination.
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The combination of wildcard
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routes and routing redirects can provide an economical
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mechanism for routing traffic.
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.Pp
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One opens the channel for passing routing control messages
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by using the socket call shown in the synopsis above:
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.Pp
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The
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.Fa family
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parameter may be
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.Dv AF_UNSPEC
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which will provide
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routing information for all address families, or can be restricted
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to a specific address family by specifying which one is desired.
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There can be more than one routing socket open per system.
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.Pp
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Messages are formed by a header followed by a small
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number of sockaddrs (now variable length particularly
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in the
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.Tn ISO
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case), interpreted by position, and delimited
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by the new length entry in the sockaddr.
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An example of a message with four addresses might be an
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.Tn ISO
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redirect:
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Destination, Netmask, Gateway, and Author of the redirect.
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The interpretation of which address are present is given by a
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bit mask within the header, and the sequence is least significant
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to most significant bit within the vector.
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.Pp
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Any messages sent to the kernel are returned, and copies are sent
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to all interested listeners.
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The kernel will provide the process
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ID for the sender, and the sender may use an additional sequence
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field to distinguish between outstanding messages.
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However, message replies may be lost when kernel buffers are exhausted.
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.Pp
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The kernel may reject certain messages, and will indicate this
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by filling in the
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.Ar rtm_errno
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field.
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The routing code returns
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.Er EEXIST
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if
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requested to duplicate an existing entry,
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.Er ESRCH
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if
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requested to delete a non-existent entry,
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or
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.Er ENOBUFS
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if insufficient resources were available
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to install a new route.
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In the current implementation, all routing processes run locally,
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and the values for
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.Ar rtm_errno
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are available through the normal
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.Em errno
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mechanism, even if the routing reply message is lost.
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.Pp
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A process may avoid the expense of reading replies to
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its own messages by issuing a
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.Xr setsockopt 2
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call indicating that the
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.Dv SO_USELOOPBACK
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option
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at the
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.Dv SOL_SOCKET
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level is to be turned off.
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A process may ignore all messages from the routing socket
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by doing a
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.Xr shutdown 2
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system call for further input.
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.Pp
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If a route is in use when it is deleted,
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the routing entry will be marked down and removed from the routing table,
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but the resources associated with it will not
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be reclaimed until all references to it are released.
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User processes can obtain information about the routing
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entry to a specific destination by using a
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.Dv RTM_GET
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message, or by calling
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.Xr sysctl 3 .
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.Pp
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Messages include:
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.Bd -literal
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#define RTM_ADD 0x1 /* Add Route */
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#define RTM_DELETE 0x2 /* Delete Route */
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#define RTM_CHANGE 0x3 /* Change Metrics, Flags, or Gateway */
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#define RTM_GET 0x4 /* Report Information */
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#define RTM_LOSING 0x5 /* Kernel Suspects Partitioning */
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#define RTM_REDIRECT 0x6 /* Told to use different route */
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#define RTM_MISS 0x7 /* Lookup failed on this address */
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#define RTM_LOCK 0x8 /* fix specified metrics */
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#define RTM_RESOLVE 0xb /* request to resolve dst to LL addr - unused */
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#define RTM_NEWADDR 0xc /* address being added to iface */
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#define RTM_DELADDR 0xd /* address being removed from iface */
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#define RTM_IFINFO 0xe /* iface going up/down etc. */
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#define RTM_NEWMADDR 0xf /* mcast group membership being added to if */
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#define RTM_DELMADDR 0x10 /* mcast group membership being deleted */
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#define RTM_IFANNOUNCE 0x11 /* iface arrival/departure */
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.Ed
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.Pp
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A message header consists of one of the following:
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.Bd -literal
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struct rt_msghdr {
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u_short rtm_msglen; /* to skip over non-understood messages */
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u_char rtm_version; /* future binary compatibility */
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u_char rtm_type; /* message type */
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u_short rtm_index; /* index for associated ifp */
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int rtm_flags; /* flags, incl. kern & message, e.g. DONE */
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int rtm_addrs; /* bitmask identifying sockaddrs in msg */
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pid_t rtm_pid; /* identify sender */
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int rtm_seq; /* for sender to identify action */
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int rtm_errno; /* why failed */
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int rtm_use; /* from rtentry */
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u_long rtm_inits; /* which metrics we are initializing */
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struct rt_metrics rtm_rmx; /* metrics themselves */
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};
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struct if_msghdr {
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u_short ifm_msglen; /* to skip over non-understood messages */
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u_char ifm_version; /* future binary compatibility */
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u_char ifm_type; /* message type */
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int ifm_addrs; /* like rtm_addrs */
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int ifm_flags; /* value of if_flags */
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u_short ifm_index; /* index for associated ifp */
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struct if_data ifm_data; /* statistics and other data about if */
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};
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struct ifa_msghdr {
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u_short ifam_msglen; /* to skip over non-understood messages */
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u_char ifam_version; /* future binary compatibility */
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u_char ifam_type; /* message type */
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int ifam_addrs; /* like rtm_addrs */
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int ifam_flags; /* value of ifa_flags */
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u_short ifam_index; /* index for associated ifp */
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int ifam_metric; /* value of ifa_metric */
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};
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struct ifma_msghdr {
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u_short ifmam_msglen; /* to skip over non-understood messages */
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u_char ifmam_version; /* future binary compatibility */
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u_char ifmam_type; /* message type */
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int ifmam_addrs; /* like rtm_addrs */
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int ifmam_flags; /* value of ifa_flags */
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u_short ifmam_index; /* index for associated ifp */
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};
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struct if_announcemsghdr {
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u_short ifan_msglen; /* to skip over non-understood messages */
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u_char ifan_version; /* future binary compatibility */
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u_char ifan_type; /* message type */
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u_short ifan_index; /* index for associated ifp */
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char ifan_name[IFNAMSIZ]; /* if name, e.g. "en0" */
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u_short ifan_what; /* what type of announcement */
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};
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.Ed
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.Pp
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The
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.Dv RTM_IFINFO
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message uses a
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.Ar if_msghdr
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header, the
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.Dv RTM_NEWADDR
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and
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.Dv RTM_DELADDR
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messages use a
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.Ar ifa_msghdr
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header, the
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.Dv RTM_NEWMADDR
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and
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.Dv RTM_DELMADDR
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messages use a
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.Vt ifma_msghdr
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header, the
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.Dv RTM_IFANNOUNCE
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message uses a
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.Vt if_announcemsghdr
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header,
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and all other messages use the
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.Ar rt_msghdr
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header.
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.Pp
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The
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.Dq Li "struct rt_metrics"
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and the flag bits are as defined in
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.Xr rtentry 9 .
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.Pp
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Specifiers for metric values in rmx_locks and rtm_inits are:
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.Bd -literal
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#define RTV_MTU 0x1 /* init or lock _mtu */
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#define RTV_HOPCOUNT 0x2 /* init or lock _hopcount */
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#define RTV_EXPIRE 0x4 /* init or lock _expire */
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#define RTV_RPIPE 0x8 /* init or lock _recvpipe */
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#define RTV_SPIPE 0x10 /* init or lock _sendpipe */
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#define RTV_SSTHRESH 0x20 /* init or lock _ssthresh */
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#define RTV_RTT 0x40 /* init or lock _rtt */
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#define RTV_RTTVAR 0x80 /* init or lock _rttvar */
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.Ed
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.Pp
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Specifiers for which addresses are present in the messages are:
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.Bd -literal
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#define RTA_DST 0x1 /* destination sockaddr present */
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#define RTA_GATEWAY 0x2 /* gateway sockaddr present */
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#define RTA_NETMASK 0x4 /* netmask sockaddr present */
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#define RTA_GENMASK 0x8 /* cloning mask sockaddr present - unused */
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#define RTA_IFP 0x10 /* interface name sockaddr present */
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#define RTA_IFA 0x20 /* interface addr sockaddr present */
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#define RTA_AUTHOR 0x40 /* sockaddr for author of redirect */
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#define RTA_BRD 0x80 /* for NEWADDR, broadcast or p-p dest addr */
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.Ed
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.Sh SEE ALSO
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.Xr sysctl 3 ,
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.Xr route 8 ,
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.Xr rtentry 9
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.Pp
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The constants for the
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.Va rtm_flags
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field are documented in the manual page for the
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.Xr route 8
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utility.
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.Sh HISTORY
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A
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.Dv PF_ROUTE
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protocol family first appeared in
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.Bx 4.3 reno .
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