nanog mailing list archives

Re: What's the point of prepend communities?


From: Michael Hallgren <mh () xalto net>
Date: Mon, 30 Oct 2017 19:56:43 +0100

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 () 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 () ufp org
PGP keys at http://www.ufp.org/~bicknell/


Current thread: