What is the function of BGP confederations?

Question

Options

• AThey require routers to use private AS numbers.
• BThey eliminate the need for a fully-meshed internal BGP design.
• CThey enable a single device to distribute a common configuration to its peers.
• DThey assign an external BGP router to serve as the route reflector.

• A
  3% (2)
• B
  86% (55)
• C
  8% (5)
• D
  3% (2)

Explanation

In a large BGP AS, iBGP requires a full mesh of sessions between all internal BGP speakers because iBGP does not re-advertise routes learned from one iBGP peer to another. This becomes operationally unscalable as the number of routers grows (n*(n-1)/2 sessions). BGP confederations solve this by dividing the AS into multiple sub-ASes (confederation member ASes), typically using private AS numbers from the range 64512–65534. Within the confederation, sub-ASes use eBGP-like sessions between each other while maintaining iBGP sessions within each sub-AS. To the outside world, the entire confederation appears as a single AS. This eliminates the full-mesh iBGP requirement across the entire domain. Option A is partially accurate (private AS numbers are typically used) but is a mechanism, not the function. Option C describes route reflectors or BGP template peers. Option D describes route reflectors, not confederations.

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