1130b656e5
This will make a number of things easier in the future, as well as (finally!) avoiding the Id-smashing problem which has plagued developers for so long. Boy, I'm glad we're not using sup anymore. This update would have been insane otherwise.
285 lines
8.7 KiB
Groff
285 lines
8.7 KiB
Groff
.\" Copyright (c) 1983, 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: @(#)inet.4 8.1 (Berkeley) 6/5/93
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.\" $FreeBSD$
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.\"
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.Dd February 14, 1995
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.Dt INET 4
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.Os BSD 4.2
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.Sh NAME
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.Nm inet
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.Nd Internet protocol family
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.Sh SYNOPSIS
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.Fd #include <sys/types.h>
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.Fd #include <netinet/in.h>
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.Sh DESCRIPTION
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The Internet protocol family is a collection of protocols
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layered atop the
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.Em Internet Protocol
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.Pq Tn IP
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transport layer, and utilizing the Internet address format.
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The Internet family provides protocol support for the
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.Dv SOCK_STREAM , SOCK_DGRAM ,
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and
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.Dv SOCK_RAW
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socket types; the
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.Dv SOCK_RAW
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interface provides access to the
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.Tn IP
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protocol.
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.Sh ADDRESSING
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Internet addresses are four byte quantities, stored in
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network standard format (on the
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.Tn VAX
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these are word and byte
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reversed). The include file
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.Aq Pa netinet/in.h
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defines this address
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as a discriminated union.
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.Pp
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Sockets bound to the Internet protocol family utilize
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the following addressing structure,
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.Bd -literal -offset indent
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struct sockaddr_in {
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short sin_family;
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u_short sin_port;
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struct in_addr sin_addr;
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char sin_zero[8];
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};
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.Ed
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.Pp
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Sockets may be created with the local address
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.Dv INADDR_ANY
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to effect
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.Dq wildcard
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matching on incoming messages.
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The address in a
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.Xr connect 2
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or
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.Xr sendto 2
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call may be given as
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.Dv INADDR_ANY
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to mean
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.Dq this host .
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The distinguished address
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.Dv INADDR_BROADCAST
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is allowed as a shorthand for the broadcast address on the primary
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network if the first network configured supports broadcast.
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.Sh PROTOCOLS
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The Internet protocol family is comprised of
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the
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.Tn IP
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network protocol, Internet Control
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Message Protocol
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.Pq Tn ICMP ,
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Internet Group Management Protocol
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.Pq Tn IGMP ,
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Transmission Control
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Protocol
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.Pq Tn TCP ,
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and User Datagram Protocol
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.Pq Tn UDP .
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.Tn TCP
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is used to support the
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.Dv SOCK_STREAM
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abstraction while
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.Tn UDP
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is used to support the
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.Dv SOCK_DGRAM
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abstraction. A raw interface to
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.Tn IP
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is available
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by creating an Internet socket of type
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.Dv SOCK_RAW .
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The
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.Tn ICMP
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message protocol is accessible from a raw socket.
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.Pp
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The 32-bit Internet address contains both network and host parts.
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However, direct examination of addresses is discouraged. For those
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programs which absolutely need to break addresses into their component
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parts, the following
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.Xr ioctl 2
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commands are provided for a datagram socket in the Internet domain;
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they have the same form as the
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.Dv SIOCIFADDR
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command (see
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.Xr intro 4 ) .
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.Pp
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.Bl -tag -width SIOCSIFNETMASK
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.It Dv SIOCSIFNETMASK
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Set interface network mask.
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The network mask defines the network part of the address;
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if it contains more of the address than the address type would indicate,
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then subnets are in use.
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.It Dv SIOCGIFNETMASK
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Get interface network mask.
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.El
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.Sh ROUTING
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The current implementation of Internet protocols includes some routing-table
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adaptations to provide enhanced caching of certain end-to-end
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information necessary for Transaction TCP and Path MTU Discovery. The
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following changes are the most significant:
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.Bl -enum
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.It
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All IP routes, except those with the
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.Dv RTF_CLONING
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flag and those to multicast destinations, have the
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.Dv RTF_PRCLONING
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flag forcibly enabled (they are thus said to be
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.Dq "protocol cloning" ).
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.It
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When the last reference to an IP route is dropped, the route is
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examined to determine if it was created by cloning such a route. If
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this is the case, the
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.Dv RTF_PROTO3
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flag is turned on, and the expiration timer is initialized to go off
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in net.inet.ip.rtexpire seconds. If such a route is re-referenced,
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the flag and expiration timer are reset.
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.It
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A kernel timeout runs once every ten minutes, or sooner if there are
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soon-to-expire routes in the kernel routing table, and deletes the
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expired routes.
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.El
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.Pp
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A dynamic process is in place to modify the value of
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net.inet.ip.rtexpire if the number of cached routes grows too large.
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If after an expiration run there are still more than
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net.inet.ip.rtmaxcache unreferenced routes remaining, the rtexpire
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value is multiplied by 3/4, and any routes which have longer
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expiration times have those times adjusted. This process is damped
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somewhat by specification of a minimum rtexpire value
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(net.inet.ip.rtminexpire), and by restricting the reduction to once in
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a ten-minute period.
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.Pp
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If some external process deletes the original route from which a
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protocol-cloned route was generated, the ``child route'' is deleted.
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(This is actually a generic mechanism in the routing code support for
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protocol-requested cloning.)
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.Pp
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No attempt is made to manage routes which were not created by protocol
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cloning; these are assumed to be static, under the management of an
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external routing process, or under the management of a link layer
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(e.g.,
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.Tn ARP
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for Ethernets).
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.Pp
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Only certain types of network activity will result in the cloning of a
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route using this mechanism. Specifically, those protocols (such as
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.Tn TCP
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and
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.Tn UDP )
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which themselves cache a long-lasting reference to route for a destination
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will trigger the mechanism; whereas raw
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.Tn IP
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packets, whether locally-generated or forwarded, will not.
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.Sh MIB VARIABLES
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A number of variables are implemented in the net.inet branch of the
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.Xr sysctl 3
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MIB. In addition to the variables supported by the transport
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protocols (for which see the respective manual pages), the following
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general variables are defined:
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.Bl -tag -width IPCTL_SENDREDIRECTS
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.It Dv IPCTL_FORWARDING
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.Pq ip.forwarding
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Boolean: enable/disable forwarding of IP packets (default depends on
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the
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.Dv GATEWAY
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kernel configuration option).
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.It Dv IPCTL_SENDREDIRECTS
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.Pq ip.redirect
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Boolean: enable/disable sending of ICMP redirects in response to
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unforwardable
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.Tn IP
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packets (default true).
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.It Dv IPCTL_DEFTTL
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.Pq ip.ttl
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Integer: default time-to-live
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.Pq Dq TTL
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to use for outgoing
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.Tn IP
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packets.
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.It Dv IPCTL_SOURCEROUTE
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.Pq ip.sourceroute
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Boolean: enable/disable forwarding of source-routed IP packets (default false).
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.It Dv IPCTL_RTEXPIRE
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.Pq ip.rtexpire
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Integer: lifetime in seconds of protocol-cloned
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.Tn IP
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routes after the last reference drops (default one hour). This value
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varies dynamically as described above.
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.It Dv IPCTL_RTMINEXPIRE
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.Pq ip.rtminexpire
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Integer: minimum value of ip.rtexpire (default ten seconds). This
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value has no effect on user modifications, but restricts the dynamic
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adaptation described above.
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.It Dv IPCTL_RTMAXCACHE
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.Pq ip.rtmaxcache
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Integer: trigger level of cached, unreferenced, protocol-cloned routes
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which initiates dynamic adaptation (default 128).
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.El
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.Sh SEE ALSO
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.Xr ioctl 2 ,
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.Xr socket 2 ,
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.Xr sysctl 3 ,
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.Xr icmp 4 ,
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.Xr igmp 4 ,
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.Xr intro 4 ,
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.Xr ip 4 ,
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.Xr tcp 4 ,
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.Xr ttcp 4 ,
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.Xr udp 4
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.Rs
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.%T "An Introductory 4.3 BSD Interprocess Communication Tutorial"
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.%B PS1
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.%N 7
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.Re
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.Rs
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.%T "An Advanced 4.3 BSD Interprocess Communication Tutorial"
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.%B PS1
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.%N 8
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.Re
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.Sh CAVEAT
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The Internet protocol support is subject to change as
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the Internet protocols develop. Users should not depend
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on details of the current implementation, but rather
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the services exported.
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.Sh HISTORY
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The
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.Nm
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protocol interface appeared in
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.Bx 4.2 .
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The
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.Dq protocol cloning
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code appeared in
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.Fx 2.1 .
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