Diff between no-export and local-as

Unanswered Question
Jul 16th, 2007
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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?

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mheusing Mon, 07/16/2007 - 04:48
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  • Cisco Employee,

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

gauravsukhadia Fri, 05/12/2017 - 11:36
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From the TCP/IP volume II ,

"no-export" community is also applicable in case of confederation.

Still find no difference.

NO_EXPORT (4294967041, or 0xFFFFFF01)— Routes received carrying this value cannot
be advertised to EBGP peers or, if a confederation is configured, the routes cannot be
advertised outside of the confederation. 


LOCAL_AS (4294967043, or 0xFFFFFF03)— RFC 1997 calls this attribute
NO_EXPORT_SUBCONFED. Routes received carrying this value cannot be advertised to EBGP
peers, including peers in other autonomous systems within a confederation.


Thanks,

Gaurav Sukhadia


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