231 lines
6.6 KiB
Groff
231 lines
6.6 KiB
Groff
.\" $NetBSD: esis.4,v 1.13 2003/08/07 10:31:01 agc Exp $
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.\"
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.\" 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. 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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.\" @(#)esis.4 8.2 (Berkeley) 11/30/93
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.\"
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.Dd November 30, 1993
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.Dt ESIS 4
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.Os
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.Sh NAME
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.Nm esis
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.Nd End System to Intermediate System Routing Protocol
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.Sh SYNOPSIS
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.In sys/types.h
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.In netiso/esis.h
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.Sh DESCRIPTION
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The
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.Tn ES-IS
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routing protocol is used to dynamically map between
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.Tn ISO NSAP
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addresses and
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.Tn ISO SNPA
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addresses; to permit End Systems (ES) and Intermediate Systems (IS)
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to learn of each other's existence; and to allow Intermediate Systems
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to inform End Systems of (potentially) better routes to use when forwarding
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Network Protocol Data Units
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.Pq Tn NPDU Ns s
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to a particular destination.
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.Pp
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The mapping between
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.Tn NSAP
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addresses and
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.Tn SNPA
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addresses is accomplished by transmitting
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.Qq hello
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Protocol Data Units
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.Pq Tn PDU Ns s
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between the cooperating Systems.
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These
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.Tn PDU Ns s
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are transmitted whenever the
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.Em configuration
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timer expires.
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When a
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.Qq hello
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.Tn PDU
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is received, the
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.Tn SNPA
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address that it conveys is stored in the routing table for as long as the
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.Em holding time
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in the
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.Tn PDU
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suggests.
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The default
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.Em holding time
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(120 seconds) placed in the
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.Qq hello
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.Tn PDU ,
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the configuration timer value, and the system type (End System or
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Intermediate System) may be changed by issuing an
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.Dv SIOCSSTYPE
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.Xr ioctl 2 ,
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which is defined in
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.Aq Pa sys/netiso/iso_snpac.h .
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.Pp
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The protocol behaves differently depending on whether the System is
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configured as an End System or an Intermediate System.
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.Sh END SYSTEM OPERATION
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When an interface requests a mapping for an address not in the cache, the
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.Tn SNPA
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of any known Intermediate System is returned.
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If an Intermediate System is not known, then the
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.Em all end systems
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multicast address is returned.
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It is assumed that the intended recipient of the
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.Tn NPDU
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will immediately transmit a
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.Qq hello
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.Tn PDU
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back to the originator of the
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.Tn NPDU .
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.Pp
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If an
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.Tn NPDU
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is forwarded by the End System, a redirect
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.Tn PDU
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will not be generated.
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However, redirect
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.Tn PDU Ns s
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received will be processed.
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This processing consists of adding an entry in the routing table.
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If the redirect is towards an Intermediate System, then an entry
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is made in the routing table as well.
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The entry in the routing table will mark the
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.Tn NSAP
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address contained in the redirect
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.Tn PDU
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as the gateway for the destination
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system (if an NET is supplied), or will create a route with
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the
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.Tn NSAP
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address as the destination and the
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.Tn SNPA
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address (embodied as a link-level struct sockaddr) as the
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gateway.
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.Pp
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If the System is configured as an End System, it will report all the
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.Tn NSAP Ns s
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that have been configured using the
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.Xr ifconfig 8
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command, and no others.
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It is possible to have more than one
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.Tn NSAP
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assigned to a given interface,
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and it is also possible to have the same
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.Tn NSAP
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assigned to multiple
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interfaces.
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However, any
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.Tn NSAP
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containing an
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.Tn NSEL
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that is consistent with the
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.Em nsellength
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option (default one) of any interface will be accepted as an
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.Tn NSAP
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for this System.
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.Sh INTERMEDIATE SYSTEM OPERATION
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When an interface requests a mapping for an address not in the routing table,
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an error is returned.
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.Pp
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When an
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.Tn NPDU
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is forwarded out on the same interface that the
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.Tn NPDU
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arrived upon, a redirect
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.Tn PDU
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is generated.
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.Sh MANUAL ROUTING TABLE MODIFICATION
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To facilitate communications with systems which do not use
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.Tn ES-IS ,
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one may add a route whose destination is a struct sockaddr_iso containing the
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.Tn NSAP
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in question, and the gateway being a link-level struct sockaddr,
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either by writing a special purpose program, or using the
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.Xr route 8
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command e.g.:
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.Bd -literal
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route add -iface -osi 49.0.4.8.0.2b.b.83.bf \
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-link qe0:8.0.2b.b.83.bf
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.Ed
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.Pp
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If the System is configured as an End System and has a single
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network interface which does not support multicast reception, it
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is necessary to manually configure the location of an
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.Tn IS ,
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using the route command in a similar way.
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There, the destination address should be
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.Dq default
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(spelled out literally as 7
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.Tn ASCII
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characters), and the gateway should be once again be a link-level
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struct sockaddr specifying the
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.Tn SNPA
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of the
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.Tn IS .
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.Sh SEE ALSO
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.Xr iso 4 ,
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.\" .Xr un 4 ,
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.Xr ifconfig 8 ,
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.Xr route 8
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.Rs
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.%T "End system to Intermediate system routing exchange protocol for use in conjunction with the Protocol for providing the connectionless-mode network service"
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.%R ISO
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.%N 9542
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.Re
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.Sh BUGS
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Redirect
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.Tn PDU Ns s
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do not contain options from the forwarded
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.Tn NPDU
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which generated the redirect.
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The multicast address used on the
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.Tn IEEE 802.3
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.Pq Tn Ethernet
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network is taken from the
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National Bureau of Standards
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.Pq Tn NBS
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December 1987 agreements.
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This multicast address is not compatible with the
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.Tn IEEE 802.5
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.Pq Tn Token Ring
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multicast addresses format.
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Therefore, broadcast addresses are used on the
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.Tn IEEE 802.5
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subnetwork.
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.Pp
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Researchers at the University of Wisconsin are constructing an implementation
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of the
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.Tn IS-IS
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routing protocol.
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.Pp
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.Tn NBS
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is now known as the National Institute for Standards and Technology
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.Pq Tn NIST .
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