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Cisco® BGP-4 Command and Configuration Handbook (CCIE Professional Development) by William R. Parkhurst Ph.D.

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3-8. bgp confederation peers 1_or_more_AS-numbers

Syntax Description:

  • AS-number— AS number used with EBGP neighbors.

  • 1_or_more_AS-numbers— AS number(s) of directly connected peers that are in a different sub-AS.

Purpose: IBGP neighbors do not propagate routing information learned from one IBGP neighbor to another IBGP neighbor. If you are running IBGP, every IBGP speaker must have a connection to every other IBGP speaker in the AS. This becomes a scaling problem as the number of IBGP speakers increases. The number of IBGP connections for n speakers is [n(n–1)]/2. Table 3-1 lists the number of connections needed for two to ten IBGP speakers.

Table 3-1. IBGP Connections Needed for a Full Mesh
Number of IBGP Speakers Number of Connections
2 1
3

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