Re: What's the point of prepend communities?

In a message written on Thu, Oct 26, 2017 at 02:47:44PM -0400, Jason Lixfeld wrote:

I understand how prepends fit in the context of best path selection, but my question was more the difference between a customer signalling the ISP to prepend their AS using a BGP community stamped to a prefix vs. the customer prepending their own AS instead.

Imagine: You are 1. ISP is 2. ISP's peers are 3 & 4. Your B2B partner is 5. 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 3 3 5 1 2 4 5 And you just forced all traffic to the second, shorter path. -- Leo Bicknell - bicknell@ufp.org PGP keys at http://www.ufp.org/~bicknell/