MirOS Manual: esis(4)

ESIS(4)                    BSD Programmer's Manual                     ESIS(4)

NAME

     ES-IS - End System to Intermediate System Routing Protocol

SYNOPSIS

     pseudo-device ether [count]

DESCRIPTION

     The ES-IS routing protocol is used to dynamically map between ISO NSAP
     addresses and ISO SNPA addresses; to permit End and Intermediate Systems
     to learn of each other's existence; and to allow Intermediate Systems to
     inform End Systems of (potentially) better routes to use when forwarding
     NPDUs to a particular destination.

     The mapping between NSAP addresses and SNPA addresses is accomplished by
     transmitting hello PDUs between the cooperating Systems. These PDUs are
     transmitted whenever the configuration timer expires. When a hello PDU is
     received, the SNPA address that it conveys is stored in the routing table
     for as long as the holding time in the PDU suggests. The default holding
     time (120 seconds) placed in the hello PDU, the configuration timer
     value, and the system type (End System or Intermediate System) may be
     changed by issuing an SIOCSSTYPE ioctl(2), which is defined in
     /sys/netiso/iso_snpac.h.

     The protocol behaves differently depending on whether the System is con-
     figured as an End System or an Intermediate System.

END SYSTEM OPERATION

     When an interface requests a mapping for an address not in the cache, the
     SNPA of any known Intermediate System is returned. If an Intermediate
     System is not known, then the all end systems multicast address is re-
     turned. It is assumed that the intended recipient of the NPDU will im-
     mediately transmit a hello PDU back to the originator of the NPDU.

     If an NPDU is forwarded by the End System, a redirect PDU will not be
     generated. However, redirect PDUs received will be processed. This pro-
     cessing consists of adding an entry in the routing table. If the redirect
     is towards an Intermediate System, then an entry is made in the routing
     table as well. The entry in the routing table will mark the NSAP address
     contained in the redirect PDU as the gateway for the destination system
     (if an NET is supplied), or will create a route with the NSAP address as
     the destination and the SNPA address (embodied as a link-level sockaddr)
     as the gateway.

     If the System is configured as an End System, it will report all the
     NSAPs that have been configured using the ifconfig command, and no oth-
     ers. It is possible to have more than one NSAP assigned to a given inter-
     face, and it is also possible to have the same NSAP assigned to multiple
     interfaces. However, any NSAP containing an NSEL that is consistent with
     the nsellength option (default one) of any interface will be accepted as
     an NSAP for this System.

INTERMEDIATE SYSTEM OPERATION

     When an interface requests a mapping for an address not in the routing
     table, an error is returned.

     When an NPDU is forwarded out on the same interface that the NPDU arrived
     upon, a redirect PDU is generated.

MANUAL ROUTING TABLE MODIFICATION

     To facilitate communications with systems which do not use ES-IS, one may
     add a route whose destination is a sockaddr_iso containing the NSAP in
     question, and the gateway being a link-level sockaddr, either by writing
     a special purpose program, or using the route(8) command e.g.:

     route add -iface -osi 49.0.4.8.0.2b.b.83.bf -link qe0:8.0.2b.b.83.bf

     If the System is configured as an End System and has a single network in-
     terface which does not support multicast reception, it is necessary to
     manually configure the location of an IS, using the route command in a
     similar way. There, the destination address should be "default" (spelled
     out literally as 7 ASCII characters), and the gateway should be once
     again be a link-level sockaddr specifying the SNPA of the IS.

SEE ALSO

     iso(4), ifconfig(8), route(8)

     End system to Intermediate system routing exchange protocol for use in
     conjunction with the Protocol for providing the connectionless-mode
     network service, ISO, 9542.

BUGS

     Redirect PDUs do not contain options from the forwarded NPDU which gen-
     erated the redirect. The multicast address used on the 802.3 network is
     taken from the NBS December 1987 agreements. This multicast address is
     not compatible with the 802.5 (Token Ring) multicast addresses format.
     Therefore, broadcast addresses are used on the 802.5 subnetwork.
     Researchers at the University of Wisconsin are constructing an implemen-
     tation of the IS-IS routing protocol.

MirOS BSD #10-current         November 30, 1993                              1

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