4.4BSD/usr/share/man/cat4/esis.0

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

NNAAMMEE
     eess--iiss - End System to Intermediate System Routing Protocol

SSYYNNOOPPSSIISS
     ppsseeuuddoo--ddeevviiccee
     eetthheerr

DDEESSCCRRIIPPTTIIOONN
     The EESS--IISS 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 _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(2),  which is defined in
     _/_s_y_s_/_n_e_t_i_s_o_/_i_s_o___s_n_p_a_c_._h_.

     The protocol behaves differently depending on whether the System is con-
     figured 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 re-
     turned. It is assumed that the intended recipient of the NPDU will imme-
     diately 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 may mark the NSAP ad-
     dress 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 ad-
     dress 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 in-
     terface, and it is also possible to have the same NSAP assigned to multi-
     ple interfaces.  However, any NSAP containing an NSEL that is consistent
     with the nsellength option (default one) of any interface will be accept-
     ed 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 EESS--IISS,, 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.

SSEEEE AALLSSOO
     un(4),  iso(4),  route(8),  ifconfig(8)

     _E_n_d _s_y_s_t_e_m _t_o _I_n_t_e_r_m_e_d_i_a_t_e _s_y_s_t_e_m _r_o_u_t_i_n_g _e_x_c_h_a_n_g_e _p_r_o_t_o_c_o_l _f_o_r _u_s_e _i_n
     _c_o_n_j_u_n_c_t_i_o_n _w_i_t_h _t_h_e _P_r_o_t_o_c_o_l _f_o_r _p_r_o_v_i_d_i_n_g _t_h_e _c_o_n_n_e_c_t_i_o_n_l_e_s_s_-_m_o_d_e
     _n_e_t_w_o_r_k _s_e_r_v_i_c_e, ISO, 9542.

BBUUGGSS
     Redirect PDUs do not contain options from the forwarded NPDU which gener-
     ated 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.  Re-
     searchers at the University of Wisconsin are constructing an implementa-
     tion of the IS-IS routing protocol.

4.4BSD                           June 9, 1993                                2