1.\" Copyright (c) 1990, 1991, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" %sccs.include.redist.man% 5.\" 6.\" @(#)esis.4 8.1 (Berkeley) 06/09/93 7.\" 8.Dd 9.Dt ESIS 4 10.Os 11.Sh NAME 12.Nm es-is 13.Nd End System to Intermediate System Routing Protocol 14.Sh SYNOPSIS 15.Sy pseudo-device 16.Nm ether 17.Sh DESCRIPTION 18The 19.Nm ES-IS 20routing protocol is used to dynamically map between 21.Tn ISO NSAP 22addresses and 23.Tn ISO SNPA 24addresses; to permit End and Intermediate Systems 25to learn of each other's existence; and to allow Intermediate Systems 26to inform End Systems of (potentially) better routes to use when 27forwarding 28.Tn NPDU Ns s 29to a particular destination. 30.Pp 31The mapping between 32.Tn NSAP 33addresses and 34.Tn SNPA 35addresses is accomplished by 36transmitting hello 37.Tn PDU Ns s 38between the cooperating Systems. These 39.Tn PDU Ns s 40are transmitted whenever the 41.Em configuration 42timer expires. 43When a hello 44.Tn PDU 45is received, the 46.Tn SNPA 47address that it conveys is stored in the routing table for as long as the 48.Em holding time 49in the 50.Tn PDU 51suggests. The default 52.Em holding time 53(120 seconds) placed in the hello 54.Tn PDU , 55the configuration timer value, 56and the system type (End System or Intermediate System) may be changed by 57issuing an 58.Dv SIOCSSTYPE 59.Xr ioctl 2 , 60which is defined in 61.Pa /sys/netiso/iso_snpac.h. 62.Pp 63The protocol behaves differently depending on whether the System is 64configured as an End System or an Intermediate System. 65.Sh END SYSTEM OPERATION 66When an interface requests a mapping for an address not in the cache, 67the 68.Tn SNPA 69of any known Intermediate System is returned. If an Intermediate 70System is not known, then the 71.Em all end systems 72multicast address 73is returned. It is assumed that the intended recipient of the NPDU will 74immediately transmit a hello 75.Tn PDU 76back to the originator of the 77.Tn NPDU . 78.Pp 79If an 80.Tn NPDU 81is forwarded by the End System, a redirect 82.Tn PDU 83will not be 84generated. 85However, redirect 86.Tn PDU Ns s 87received will be processed. This processing 88consists of adding an entry in the routing table. If the 89redirect is towards an Intermediate System, then an entry is made in the 90routing table as well. 91The entry in the routing table will may mark the 92.Tn NSAP 93address contained in the redirect 94.Tn PDU 95as the gateway for the destination 96system (if an NET is supplied), or will create a route with 97the NSAP address as the 98destination and the 99.Tn SNPA 100address (embodied as a link-level sockaddr) as the 101gateway. 102.Pp 103If the System is configured as an End System, it will report all the 104.Tn NSAP Ns s 105that have been configured using the ifconfig command, and no others. 106It is possible to have more than one 107.Tn NSAP 108assigned to a given interface, 109and it is also possible to have the same 110.Tn NSAP 111assigned to multiple 112interfaces. 113However, any 114.Tn NSAP 115containing an NSEL that is consistent with the 116nsellength option (default one) of any interface will be accepted as 117an 118.Tn NSAP 119for this System. 120.Sh INTERMEDIATE SYSTEM OPERATION 121When an interface requests a mapping for an address not in the routing table, 122an error is returned. 123.Pp 124When an 125.Tn NPDU 126is forwarded out on the same interface that the 127.Tn NPDU 128arrived upon, 129a redirect 130.Tn PDU 131is generated. 132.Sh MANUAL ROUTING TABLE MODIFICATION 133.Pp 134To facilitate communications with systems which do not use 135.Nm ES-IS, 136one may add a route whose destination is a sockaddr_iso containing 137the 138.Tn NSAP 139in question, and the gateway being a link-level sockaddr, 140either by writing a special purpose program, or using the 141.Xr route 8 142command e.g.: 143.Bd -literal 144route add -iface -osi 49.0.4.8.0.2b.b.83.bf \ 145 -link qe0:8.0.2b.b.83.bf 146.Ed 147.Pp 148If the 149System is configured as an End System and has a single network interface 150which does not support multicast reception, 151it is necessary to manually configure the location of an 152.Tn IS , 153using the route command in a similar way. 154There, the destination address should be 155.Dq default 156(spelled 157out literally as 7 158.Tn ASCII 159characters), and the gateway should be 160once again be a link-level sockaddr specifying the 161.Tn SNPA 162of the 163.Tn IS . 164.Sh SEE ALSO 165.Xr un 4 , 166.Xr iso 4 , 167.Xr route 8 , 168.Xr ifconfig 8 169.Rs 170.%T "End system to Intermediate system routing exchange protocol for use in conjunction with the Protocol for providing the connectionless-mode network service" 171.%R ISO 172.%N 9542 173.Re 174.Sh BUGS 175Redirect 176.Tn PDU Ns s 177do not contain options from the forwarded 178.Tn NPDU 179which generated 180the redirect. The multicast address used on the 802.3 network is taken from 181the 182.Tn NBS 183December 1987 agreements. This multicast address is not compatible 184with the 802.5 (Token Ring) multicast addresses format. Therefore, broadcast 185addresses are used on the 802.5 subnetwork. 186Researchers at the University of Wisconsin are constructing an implementation 187of the 188.Tn IS-IS 189routing protocol. 190