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What is a BGP Confederation?

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Confederations

By its true definition, a confederation is, 

An organization which consists of a number of parties or groups united in an alliance or league.

But what is a BGP confederation?

BGP Confederation

A BGP confederation is an alternative method to route reflectors, used to reduce the number of BGP peerings within a single AS. Furthermore it is a single AS that has been subdivided into a number of internal sub-AS’s, yet still, advertise as a single AS to external peers [1] .

 

image1

Figure 1 - BGP Confederation.

 

Within the confederation, each sub-AS (inter-confederation) is assigned a private AS number (64512-65535). Though eBGP is used to peer each of the sub-AS’s, the rules of iBGP still apply to each inter-confederation i.e attributes are not altered and an iBGP full-mesh is still required.

Routing Loops

To avoid routing loops, a sub-AS uses a confederation sequence, which operates like an AS path but uses only the privately assigned sub-AS numbers. [2] These are stripped prior to the router sending UPDATEs via eBGP.

Reference

[1] "BGP confederation - Wikipedia." https://en.wikipedia.org/wiki/BGP_confederation . Accessed 18 Nov. 2017.
[2] "Understanding BGP Confederations - Technical ... - Juniper Networks." https://www.juniper.net/documentation/en_US/junos/topics/concept/routing-protocol-bgp-security-confederation-understanding.html . Accessed 18 Nov. 2017.

About the Author

RDonato

R Donato

Rick Donato is the Founder and Chief Editor of Fir3net.com. He currently works as an SDN/NFV Solutions Architect and has a keen interest in automation and the cloud.

You can find Rick on Twitter @f3lix001