RFC 1133 (rfc1133) - Page 2 of 10


Routing between the NSFNET and the DDN



Alternative Format: Original Text Document



RFC 1133         Routing between the NSFNET and the DDN    November 1989


   three Mailbridges at west coast locations.  Besides functioning as
   route servers the Mailbridges also provide for connectivity, i.e,
   packet switching, between the ARPANET and the MILNET.

   The intermediate systems between the NSFNET and the ARPANET were
   under separate administrative control, typically by a NSFNET mid-
   level network.

   For a period of time, the traffic between the NSFNET and the DDN was
   carried by three ARPANET gateways.  These ARPANET gateways were under
   the administrative control of a NSFNET mid-level network or local
   site and had direct connections to both a NSFNET NSS and an ARPANET
   PSN.  These routers had simultaneous EGP sessions with a NSFNET NSS
   as well as a DDN Mailbridge.  This resulted in making them function
   as packet switches between the two peer networks.  As network routes
   were established packets were switched between the NSFNET and the
   DDN.

   The NSFNET used three NSFNET/ARPANET gateways which had been provided
   by three different sites for redundancy purposes.  Those three sites
   were initially at Cornell University, the University of Illinois
   (UC), and Merit.  When the ARPANET connections at Cornell University
   and the University of Illinois (UC) were terminated, a similar setup
   was introduced at the Pittsburgh Supercomputer Center and at the John
   von Neumann Supercomputer Center which, together with the Merit
   connection, allowed for continued redundancy.

   As described in RFC 1092 and RFC 1093, NSFNET routing is controlled by
   a distributed policy routing database that controls the acceptance
   and distribution of routing information.  This control also extends
   to the NSFNET/ARPANET gateways.

2.1  Inbound announcement -- Routes announced from the DDN to the
     NSFNET

   In the case of the three NSFNET/ARPANET gateways, each of the
   associated NSSs accepted the DDN routes at a different metric.  The
   route with the lowest metric then was favored for the traffic towards
   the specific DDN network, but had that specific gateway to the DDN
   experienced problems with loss of routing information, one of the
   redundant gateways would take over and carry the load as a fallback
   path.  Assuming consistent DDN routing information at any of the
   three gateways, as received from the Mailbridges, only a single
   NSFNET/ARPANET gateway was used at a given time for traffic from the
   NSFNET towards the DDN, with two further gateways standing by as hot
   backups.  The metric for network announcements from the DDN to the
   NSFNET was coordinated by the Merit/NSFNET project.




Yu & Braun