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31.\"     @(#)esis.4	8.2 (Berkeley) 11/30/93
32.\"
33.Dd November 30, 1993
34.Dt ESIS 4
35.Os
36.Sh NAME
37.Nm ES-IS
38.Nd End System to Intermediate System Routing Protocol
39.Sh SYNOPSIS
40.Cd "pseudo-device ether" Op Ar count
41.Sh DESCRIPTION
42The
43.Nm ES-IS
44routing protocol is used to dynamically map between
45.Tn ISO NSAP
46addresses and
47.Tn ISO SNPA
48addresses; to permit End and Intermediate Systems
49to learn of each other's existence; and to allow Intermediate Systems
50to inform End Systems of (potentially) better routes to use when
51forwarding
52.Tn NPDU Ns s
53to a particular destination.
54.Pp
55The mapping between
56.Tn NSAP
57addresses and
58.Tn SNPA
59addresses is accomplished by
60transmitting hello
61.Tn PDU Ns s
62between the cooperating Systems.
63These
64.Tn PDU Ns s
65are transmitted whenever the
66.Em configuration
67timer expires.
68When a hello
69.Tn PDU
70is received, the
71.Tn SNPA
72address that it conveys is stored in the routing table for as long as the
73.Em holding time
74in the
75.Tn PDU
76suggests.
77The default
78.Em holding time
79(120 seconds) placed in the hello
80.Tn PDU ,
81the configuration timer value,
82and the system type (End System or Intermediate System) may be changed by
83issuing an
84.Dv SIOCSSTYPE
85.Xr ioctl 2 ,
86which is defined in
87.Pa /sys/netiso/iso_snpac.h .
88.Pp
89The protocol behaves differently depending on whether the System is
90configured as an End System or an Intermediate System.
91.Sh END SYSTEM OPERATION
92When an interface requests a mapping for an address not in the cache,
93the
94.Tn SNPA
95of any known Intermediate System is returned.
96If an Intermediate System is not known, then the
97.Em all end systems
98multicast address
99is returned.
100It is assumed that the intended recipient of the NPDU will immediately
101transmit a hello
102.Tn PDU
103back to the originator of the
104.Tn NPDU .
105.Pp
106If an
107.Tn NPDU
108is forwarded by the End System, a redirect
109.Tn PDU
110will not be
111generated.
112However, redirect
113.Tn PDU Ns s
114received will be processed.
115This processing consists of adding an entry in the routing table.
116If the redirect is towards an Intermediate System, then an entry is
117made in the routing table as well.
118The entry in the routing table will mark the
119.Tn NSAP
120address contained in the redirect
121.Tn PDU
122as the gateway for the destination
123system (if an NET is supplied), or will create a route with
124the NSAP address as the
125destination and the
126.Tn SNPA
127address (embodied as a link-level sockaddr) as the
128gateway.
129.Pp
130If the System is configured as an End System, it will report all the
131.Tn NSAP Ns s
132that have been configured using the ifconfig command, and no others.
133It is possible to have more than one
134.Tn NSAP
135assigned to a given interface,
136and it is also possible to have the same
137.Tn NSAP
138assigned to multiple
139interfaces.
140However, any
141.Tn NSAP
142containing an NSEL that is consistent with the
143nsellength option (default one) of any interface will be accepted as
144an
145.Tn NSAP
146for this System.
147.Sh INTERMEDIATE SYSTEM OPERATION
148When an interface requests a mapping for an address not in the routing table,
149an error is returned.
150.Pp
151When an
152.Tn NPDU
153is forwarded out on the same interface that the
154.Tn NPDU
155arrived upon,
156a redirect
157.Tn PDU
158is generated.
159.Sh MANUAL ROUTING TABLE MODIFICATION
160To facilitate communications with systems which do not use
161.Nm ES-IS ,
162one may add a route whose destination is a sockaddr_iso containing
163the
164.Tn NSAP
165in question, and the gateway being a link-level sockaddr,
166either by writing a special purpose program, or using the
167.Xr route 8
168command e.g.:
169.Bd -literal
170route add -iface -osi 49.0.4.8.0.2b.b.83.bf -link qe0:8.0.2b.b.83.bf
171.Ed
172.Pp
173If the
174System is configured as an End System and has a single network interface
175which does not support multicast reception,
176it is necessary to manually configure the location of an
177.Tn IS ,
178using the route command in a similar way.
179There, the destination address should be
180.Dq default
181(spelled
182out literally as 7
183.Tn ASCII
184characters), and the gateway should be
185once again be a link-level sockaddr specifying the
186.Tn SNPA
187of the
188.Tn IS .
189.Sh SEE ALSO
190.Xr iso 4 ,
191.Xr ifconfig 8 ,
192.Xr route 8
193.Rs
194.%T "End system to Intermediate system routing exchange protocol for use in conjunction with the Protocol for providing the connectionless-mode network service"
195.%R ISO
196.%N 9542
197.Re
198.Sh BUGS
199Redirect
200.Tn PDU Ns s
201do not contain options from the forwarded
202.Tn NPDU
203which generated
204the redirect.
205The multicast address used on the 802.3 network is taken from the
206.Tn NBS
207December 1987 agreements.
208This multicast address is not compatible with the 802.5 (Token Ring)
209multicast addresses format.
210Therefore, broadcast addresses are used on the 802.5 subnetwork.
211Researchers at the University of Wisconsin are constructing an implementation
212of the
213.Tn IS-IS
214routing protocol.
215