RFC 1482 (rfc1482) - Page 3 of 11

Aggregation Support in the NSFNET Policy-Based Routing Database

RFC 1482              Routing Aggregation Support              July 1993


   network numbers that were announced by the AS's in the list, *AND*
   which appear in the "restrict list" of network numbers submitted
   separately by the midlevel.

      For example,

         announcetoAS 42 restrict ASlist 22

         announce 192.135.237 

   These statements mean that AS 42 only wishes to hear announcements
   from the backbone about the nets in AS 22 which are explicitly listed
   here (i.e., net 192.135.237).

   It is also possible, when using the "restrict" keyword, to list
   specific "noannounce" lines. Those indicate that all of the networks
   listed in the routing table for the AS should be announced except
   those listed on the noannounce clauses.  (There is also a
   "noannouncetoAS" statement[4].)

2.2 New Configuration Features for Aggregation

   There will be three new capabilities for which the backbone service
   can be configured to support aggregation. The first two allow
   aggregates to be accepted and stored in the backbone routing tables
   based on announcements by the regional network (autonomous system or
   AS) peers.  The third allows the announcement of aggregates to the AS
   neighbor peers. The following sections give examples of the three
   features.

   We use the notation  to describe an aggregate.
   This refers to the IP prefix "net-IP", with a mask which has
   "prefix-length" 1's as counted from the high-order end. For example,
    is equivalent to  [5].
   (The form using prefix-length rather than the mask is more compact.)

2.2.1 NSFNET accepts aggregates

   In this case the regional peer router is CIDR-capable (i.e., runs
   BGP-4) and the announcement comes into the backbone as an IP address
   prefix.

   To illustrate this in the spirit of sec. 2.1.1:

                  1:189 2:24 3:267

   In this example, independent of the "class" of IP network number, an
   aggregate containing network addresses matching a pattern in which



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