Diff between no-export and local-as

Unanswered Question
Jul 16th, 2007

Hi

I found the following description in Cisco.com

no-export???Routes with this community are sent to peers in other subautonomous systems within a confederation. Do not advertise this route to an external BGP (eBGP) peer. External systems are those outside the confederation. If there is no confederation, an external system is any eBGP peer.

???local-as???Send this route to peers in other subautonomous systems within the local confederation. Do not advertise this route to an external system.

I dont understand the difference. Can someone please explain?

I have this problem too.
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mheusing Mon, 07/16/2007 - 04:48

Hi,

As denoted it makes a difference when used with confederations. A confederation is - oversimplified - an official AS divided internally into a set of private ASes. Example: you own AS 1 and carve it into AS 65001, 65002, 65003 and 65004. All your internet peerings will use AS 1, all your internal peerings will use 6500X.

"no-export" will keep a prefix within AS 1, which means anywhere within AS 65001 - 65004.

"local-as" will keep the prefix within the confederation AS, f.e. it will be keept within 65001 and not to 65002 - 65004.

Unless there is a specific reason within a confederation setup, use "no-export" to announce prefixes internally without leaking them to the internet.

Hope this helps! Please rate all posts.

Regards, Martin

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