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