RFC 1482 (rfc1482) - Page 2 of 11

Aggregation Support in the NSFNET Policy-Based Routing Database

RFC 1482              Routing Aggregation Support              July 1993


2. Aggregation Support by the Backbone Service

   The NSFNET backbone service includes a Policy-Based Routing Database
   system which currently holds the set of network numbers that are
   accepted by the backbone service with a list of Autonomous System
   numbers from which announcements of these network numbers are
   expected.  In order to implement CIDR, the database system will be
   modified to allow aggregation of routing information to be
   configured.

   The NSFNET will (initially) not support de-aggregation on its
   outbound announcements. See section 2.3.

2.1 Current Configuration Capabilities

2.1.1 Inbound Announcements

   An example of the way a network number is currently configured is as
   follows:

         35      1:237   2:233   3:183   4:266   5:267  6:1225

   This shows that network number 35 (ie. 35.0.0.0, a class A net
   number) is configured on the T3 backbone such that routing
   announcements are expected from up to 6 autonomous systems. The
   primary path is via AS 237, secondary is via AS 233, etc.

2.1.2 Outbound Announcements

   Currently the NSFNET database has a list of AS's or network numbers
   for each neighbor AS that are announced by the backbone to that AS.
   These announcements are specified currently by "announcetoAS"
   statements--which implement policies submitted by midlevels to
   Merit--and then included in the ANSnet router configuration files.
   There are two forms of these statements.  The first form uses the
   "norestrict" clause and indicates that all of the network numbers
   within each AS in the list should be announced to the neighbor
   midlevel AS. For example:

         announcetoAS 42 norestrict ASlist 22 26 38 60 68

   In this example, the NSFNET is configured to announce to neighboring
   midlevel AS 42, all networks in the routing table that were announced
   from AS's 22, 26, 38, 60 and 68.

   If the "norestrict" keyword is changed to "restrict", this indicates
   that an explicit announce list of network numbers for the AS is
   specified in the configuration file. The NSFNET will only announce



Knopper & Richardson