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Configuring AS Confederation Members

If you administer multiple ASs that contain a very large number of BGP systems, you can group them into one or more confederations. Each confederation is identified by its own AS number, which is called a confederation AS number. To external ASs, a confederation appears to be a single AS. Thus, the internal topology of the ASs making up the confederation is hidden.

The BGP path attributes NEXT_HOP, LOCAL_PREF, and MULTI_EXIT_DISC, which normally are restricted to a single AS, are allowed to be propagated throughout the ASs that are members of the same confederation.

Because each confederation is treated as if it were a single AS, you can apply the same routing policy to all the ASs that make up the confederation.

Grouping ASs into confederations reduces the number of BGP connections required to interconnect ASs.

If you are using BGP, you can enable the local router to participate as a member of an AS confederation. To do this, include the confederation statement:




confederation confederation-autonomous-system members [ autonomous-systems ];

For a list of hierarchy levels at which you can include this statement, see the statement summary section for this statement.

Specify the AS confederation identifier, along with the AS numbers that are members of the confederation.

Note that peer adjacencies do not form if two BGP neighbors disagree about whether an adjacency falls within a particular confederation.

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