Which BGP well-known attributes are preserved between peers with a BGP confederation?

The correct answer is C. next-hop and local-preference. BGP confederations divide a single AS into multiple sub-ASes to reduce iBGP full-mesh requirements. Within a confederation, sessions between sub-ASes behave like iBGP in two key ways: the Next-Hop attribute is preserved (not updated as it would be in standard eBGP), and the Local

Core Routing

Question

Options

Aorigin and MED
Boriginator and origin
Cnext-hop and local-preference
Dnext-hop and weight

How the community answered

(16 responses)

A
6% (1)
B
13% (2)
C
81% (13)

Explanation

BGP confederations divide a single AS into multiple sub-ASes to reduce iBGP full-mesh requirements. Within a confederation, sessions between sub-ASes behave like iBGP in two key ways: the Next-Hop attribute is preserved (not updated as it would be in standard eBGP), and the Local Preference attribute is carried across sub-AS boundaries (it would normally only be propagated within a single AS in standard iBGP). This preservation of both attributes is a defining characteristic of BGP confederation behavior. Weight is a Cisco-proprietary local attribute that is never advertised to any peer. MED is propagated across confederation sub-AS boundaries but is not always preserved. Originator-ID is a route reflector attribute. Origin is preserved in all BGP sessions regardless of confederation. The pairing of Next-Hop and Local Preference is the most precise answer for confederation-specific behavior.

Topics

#BGP Confederations#BGP Attributes#iBGP Attribute Propagation#Local-Preference

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