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NetBSD 6.1.5 - man page for esis (netbsd section 4)

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ESIS(4) 			   BSD Kernel Interfaces Manual 			  ESIS(4)

NAME
     esis -- End System to Intermediate System Routing Protocol

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

DESCRIPTION
     The ES-IS routing protocol is used to dynamically map between ISO NSAP addresses and ISO
     SNPA addresses; to permit End Systems (ES) and Intermediate 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 particular
     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 trans-
     mitted 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 configured 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 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 processing 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 sup-
     plied), 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 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 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) 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 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.

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 generated 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 compati-
     ble 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 implementation of the IS-IS
     routing protocol.

     NBS is now known as the National Institute for Standards and Technology (NIST).

BSD					November 30, 1993				      BSD
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