4.3BSD-Reno/share/man/cat4/esis.0

TP(4)			      1990			    TP(4)



NNAAMMEE
     es-is - End System to Intermediate System Routing Protocol

SSYYNNOOPPSSIISS
     ppsseeuuddoo--ddeevviiccee eetthheerr

DDEESSCCRRIIPPTTIIOONN
     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 forward-
     ing 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
     _c_o_n_f_i_g_u_r_a_t_i_o_n 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 _h_o_l_d_i_n_g _t_i_m_e in the PDU suggests.
     The default _h_o_l_d_i_n_g _t_i_m_e (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(), 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.

EENNDD SSYYSSTTEEMM OOPPEERRAATTIIOONN
     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
     _a_l_l _e_n_d _s_y_s_t_e_m_s 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 Intermedi-
     ate System, then an entry is made in the routing table as
     well.  The entry in the routing table will may 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 others.  It is possible to have more than



Printed 7/27/90               July				1






TP(4)			      1990			    TP(4)



     one NSAP assigned to a given interface, and it is also pos-
     sible 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.

IINNTTEERRMMEEDDIIAATTEE SSYYSSTTEEMM OOPPEERRAATTIIOONN
     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.

MMAANNUUAALL RROOUUTTIINNGG TTAABBLLEE MMOODDIIFFIICCAATTIIOONN
     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 gate-
     way being a link-level sockaddr, either by writing a special
     purpose program, or using the _r_o_u_t_e(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 sin-
     gle network interface which does not support multicast
     reception, it is necessary to manually configure the loca-
     tion 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 gate-
     way should be once again be a link-level sockaddr specifying
     the SNPA of the IS.

SSEEEE AALLSSOO
     un(4), iso(4F), route(8), ifconfig(8C)
     ``End system to Intermediate system routing exchange proto-
     col for use in conjunction with the Protocol for providing
     the connectionless-mode network service'' (ISO 9542).

BBUUGGSS
     Redirect PDUs do not contain options from the forwarded NPDU
     which generated the redirect. The multicast address used on
     the 802.3 network is taken from the NBS December 1987 agree-
     ments. 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 implementation of the IS-IS routing protocol.









Printed 7/27/90               July				2