Diff between no-export and local-as

[nabhishek]

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?

[mheusing]

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]

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

[r.vegam]

Thanks. This is a very good response.

[r.vegam]

Thank U. Very Good response.