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1 | .\" Copyright (c) 1990, 1991 The Regents of the University of California. |
2 | .\" All rights reserved. | |
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5 | .\" modification, are permitted provided that the following conditions | |
6 | .\" are met: | |
7 | .\" 1. Redistributions of source code must retain the above copyright | |
8 | .\" notice, this list of conditions and the following disclaimer. | |
9 | .\" 2. Redistributions in binary form must reproduce the above copyright | |
10 | .\" notice, this list of conditions and the following disclaimer in the | |
11 | .\" documentation and/or other materials provided with the distribution. | |
12 | .\" 3. All advertising materials mentioning features or use of this software | |
13 | .\" must display the following acknowledgement: | |
14 | .\" This product includes software developed by the University of | |
15 | .\" California, Berkeley and its contributors. | |
16 | .\" 4. Neither the name of the University nor the names of its contributors | |
17 | .\" may be used to endorse or promote products derived from this software | |
18 | .\" without specific prior written permission. | |
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20 | .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND | |
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30 | .\" SUCH DAMAGE. | |
31 | .\" | |
32 | .\" @(#)esis.4 6.2 (Berkeley) 3/28/91 | |
33 | .\" | |
34 | .Dd March 28, 1991 | |
35 | .Dt ESIS 4 | |
36 | .Os | |
37 | .Sh NAME | |
38 | .Nm es-is | |
39 | .Nd End System to Intermediate System Routing Protocol | |
40 | .Sh SYNOPSIS | |
41 | .Sy pseudo-device | |
42 | .Nm ether | |
43 | .Sh DESCRIPTION | |
44 | The | |
45 | .Nm ES-IS | |
46 | routing protocol is used to dynamically map between | |
47 | .Tn ISO NSAP | |
48 | addresses and | |
49 | .Tn ISO SNPA | |
50 | addresses; to permit End and Intermediate Systems | |
51 | to learn of each other's existence; and to allow Intermediate Systems | |
52 | to inform End Systems of (potentially) better routes to use when | |
53 | forwarding | |
54 | .Tn NPDU Ns s | |
55 | to a particular destination. | |
56 | .Pp | |
57 | The mapping between | |
58 | .Tn NSAP | |
59 | addresses and | |
60 | .Tn SNPA | |
61 | addresses is accomplished by | |
62 | transmitting hello | |
63 | .Tn PDU Ns s | |
64 | between the cooperating Systems. These | |
65 | .Tn PDU Ns s | |
66 | are transmitted whenever the | |
67 | .Em configuration | |
68 | timer expires. | |
69 | When a hello | |
70 | .Tn PDU | |
71 | is received, the | |
72 | .Tn SNPA | |
73 | address that it conveys is stored in the routing table for as long as the | |
74 | .Em holding time | |
75 | in the | |
76 | .Tn PDU | |
77 | suggests. The default | |
78 | .Em holding time | |
79 | (120 seconds) placed in the hello | |
80 | .Tn PDU , | |
81 | the configuration timer value, | |
82 | and the system type (End System or Intermediate System) may be changed by | |
83 | issuing an | |
84 | .Dv SIOCSSTYPE | |
85 | .Xr ioctl 2 , | |
86 | which is defined in | |
87 | .Pa /sys/netiso/iso_snpac.h. | |
88 | .Pp | |
89 | The protocol behaves differently depending on whether the System is | |
90 | configured as an End System or an Intermediate System. | |
91 | .Sh END SYSTEM OPERATION | |
92 | When an interface requests a mapping for an address not in the cache, | |
93 | the | |
94 | .Tn SNPA | |
95 | of any known Intermediate System is returned. If an Intermediate | |
96 | System is not known, then the | |
97 | .Em all end systems | |
98 | multicast address | |
99 | is returned. It is assumed that the intended recipient of the NPDU will | |
100 | immediately transmit a hello | |
101 | .Tn PDU | |
102 | back to the originator of the | |
103 | .Tn NPDU . | |
104 | .Pp | |
105 | If an | |
106 | .Tn NPDU | |
107 | is forwarded by the End System, a redirect | |
108 | .Tn PDU | |
109 | will not be | |
110 | generated. | |
111 | However, redirect | |
112 | .Tn PDU Ns s | |
113 | received will be processed. This processing | |
114 | consists of adding an entry in the routing table. If the | |
115 | redirect is towards an Intermediate System, then an entry is made in the | |
116 | routing table as well. | |
117 | The entry in the routing table will may mark the | |
118 | .Tn NSAP | |
119 | address contained in the redirect | |
120 | .Tn PDU | |
121 | as the gateway for the destination | |
122 | system (if an NET is supplied), or will create a route with | |
123 | the NSAP address as the | |
124 | destination and the | |
125 | .Tn SNPA | |
126 | address (embodied as a link-level sockaddr) as the | |
127 | gateway. | |
128 | .Pp | |
129 | If the System is configured as an End System, it will report all the | |
130 | .Tn NSAP Ns s | |
131 | that have been configured using the ifconfig command, and no others. | |
132 | It is possible to have more than one | |
133 | .Tn NSAP | |
134 | assigned to a given interface, | |
135 | and it is also possible to have the same | |
136 | .Tn NSAP | |
137 | assigned to multiple | |
138 | interfaces. | |
139 | However, any | |
140 | .Tn NSAP | |
141 | containing an NSEL that is consistent with the | |
142 | nsellength option (default one) of any interface will be accepted as | |
143 | an | |
144 | .Tn NSAP | |
145 | for this System. | |
146 | .Sh INTERMEDIATE SYSTEM OPERATION | |
147 | When an interface requests a mapping for an address not in the routing table, | |
148 | an error is returned. | |
149 | .Pp | |
150 | When an | |
151 | .Tn NPDU | |
152 | is forwarded out on the same interface that the | |
153 | .Tn NPDU | |
154 | arrived upon, | |
155 | a redirect | |
156 | .Tn PDU | |
157 | is generated. | |
158 | .Sh MANUAL ROUTING TABLE MODIFICATION | |
159 | .Pp | |
160 | To facilitate communications with systems which do not use | |
161 | .Nm ES-IS, | |
162 | one may add a route whose destination is a sockaddr_iso containing | |
163 | the | |
164 | .Tn NSAP | |
165 | in question, and the gateway being a link-level sockaddr, | |
166 | either by writing a special purpose program, or using the | |
167 | .Xr route 8 | |
168 | command e.g.: | |
169 | .Bd -literal | |
170 | route add -iface -osi 49.0.4.8.0.2b.b.83.bf \ | |
171 | -link qe0:8.0.2b.b.83.bf | |
172 | .Ed | |
173 | .Pp | |
174 | If the | |
175 | System is configured as an End System and has a single network interface | |
176 | which does not support multicast reception, | |
177 | it is necessary to manually configure the location of an | |
178 | .Tn IS , | |
179 | using the route command in a similar way. | |
180 | There, the destination address should be | |
181 | .Dq default | |
182 | (spelled | |
183 | out literally as 7 | |
184 | .Tn ASCII | |
185 | characters), and the gateway should be | |
186 | once again be a link-level sockaddr specifying the | |
187 | .Tn SNPA | |
188 | of the | |
189 | .Tn IS . | |
190 | .Sh SEE ALSO | |
191 | .Xr un 4 , | |
192 | .Xr iso 4 , | |
193 | .Xr route 8 , | |
194 | .Xr ifconfig 8 | |
195 | .Rs | |
196 | .%T "End system to Intermediate system routing exchange protocol for use in conjunction with the Protocol for providing the connectionless-mode network service" | |
197 | .%R ISO | |
198 | .%N 9542 | |
199 | .Re | |
200 | .Sh HISTORY | |
201 | The | |
202 | .Nm | |
203 | protocol implementation | |
204 | .Ud | |
205 | .Sh BUGS | |
206 | Redirect | |
207 | .Tn PDU Ns s | |
208 | do not contain options from the forwarded | |
209 | .Tn NPDU | |
210 | which generated | |
211 | the redirect. The multicast address used on the 802.3 network is taken from | |
212 | the | |
213 | .Tn NBS | |
214 | December 1987 agreements. This multicast address is not compatible | |
215 | with the 802.5 (Token Ring) multicast addresses format. Therefore, broadcast | |
216 | addresses are used on the 802.5 subnetwork. | |
217 | Researchers at the University of Wisconsin are constructing an implementation | |
218 | of the | |
219 | .Tn IS-IS | |
220 | routing protocol. |