If I understand the OP correctly, I will use this real world example: https://onestep.net/communities/as174/ 174:3001 through 174:3003 as compared to doing the prepending yourself. What is the functional difference? BGP neighbors of 174 will see just as many AS hops either way, but non-BGP customers of 174 would see you just one hop away. It's just another method of traffic engineering. ----- Mike Hammett Intelligent Computing Solutions http://www.ics-il.com Midwest-IX http://www.midwest-ix.com ----- Original Message ----- From: "Jason Lixfeld" <jason+nanog@lixfeld.ca> To: "William Herrin" <bill@herrin.us> Cc: "NANOG" <nanog@nanog.org> Sent: Thursday, October 26, 2017 1:47:44 PM Subject: Re: What's the point of prepend communities? Hi Bill,
On Oct 26, 2017, at 2:37 PM, William Herrin <bill@herrin.us> wrote:
BGP routing is based on "distance". Distance in BGP is primarily calculated as the number of ASNs in the AS Path. Prepends make a path more distance, encouraging routers to choose a different path if one is available.
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.