ESIS(4)                 NetBSD Kernel Interfaces Manual                ESIS(4)

     esis -- End System to Intermediate System Routing Protocol

     #include <sys/types.h>
     #include <netiso/esis.h>

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

     The mapping between NSAP addresses and SNPA addresses is accomplished by
     transmitting "hello" Protocol Data Units (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 con-
     veys 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 Sys-
     tem 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.

     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
     returned.  It is assumed that the intended recipient of the NPDU will
     immediately 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 redi-
     rect 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
     struct 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(8) command, and no
     others.  It is possible to have more than one NSAP assigned to a given
     interface, and it is also possible to have the same NSAP assigned to mul-
     tiple interfaces.  However, any NSAP containing an NSEL that is consis-
     tent with the nsellength option (default one) of any interface will be
     accepted as an NSAP for this System.

     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.

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

     route add -iface -osi     -link

     If the System is configured as an End System and has a single network
     interface 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 struct sockaddr specifying the SNPA of the IS.

     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.

     Redirect PDUs do not contain options from the forwarded NPDU which gener-
     ated the redirect.  The multicast address used on the IEEE 802.3
     (Ethernet) network is taken from the National Bureau of Standards (NBS)
     December 1987 agreements.  This multicast address is not compatible with
     the IEEE 802.5 (Token Ring) multicast addresses format.  Therefore,
     broadcast addresses are used on the IEEE 802.5 subnetwork.

     Researchers at the University of Wisconsin are constructing an implemen-
     tation of the IS-IS routing protocol.

     NBS is now known as the National Institute for Standards and Technology

NetBSD 5.0.1                   November 30, 1993                  NetBSD 5.0.1

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