What's the point of prepend communities?

Michael Hallgren mh at xalto.net
Mon Oct 30 18:56:43 CST 2017


Hi guys,

But keep in mind that 'prepend communities' are fragile: I decide by local preference whereto I send my traffic.

Cheers, 
mh 

Le 30 oct. 2017 à 18:25, à 18:25, Leo Bicknell <bicknell at ufp.org> a écrit:
>In a message written on Thu, Oct 26, 2017 at 01:54:17PM -0600, Clinton
>Work wrote:
>> I believe that Jason is asking about an ISP BGP community to prepend
>> their AS when the BGP routes are received from the customer (not when
>
>Yeah, I typoed my example, should have been:
>
>There are paths:
>
>1 2 3 5
>1 2 4 5
>
>If you prepend your ASN, you get:
>
>1 1 2 3 5
>1 1 2 4 5
>
>No difference.  If you send the ISP a prepend community for 3, you get:
>
>1 2 2 3 5
>1 2 4 5
>
>And you just forced all traffic to the second, shorter path.  For only
>customers that are dual homed to 3 & 4 without affecting other traffic.
>
>-- 
>Leo Bicknell - bicknell at ufp.org
>PGP keys at http://www.ufp.org/~bicknell/


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