What's the point of prepend communities?
nanog at ics-il.net
Sun Oct 29 12:01:13 CST 2017
If I understand the OP correctly, I will use this real world example:
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.
Intelligent Computing Solutions
----- Original Message -----
From: "Jason Lixfeld" <jason+nanog at lixfeld.ca>
To: "William Herrin" <bill at herrin.us>
Cc: "NANOG" <nanog at nanog.org>
Sent: Thursday, October 26, 2017 1:47:44 PM
Subject: Re: What's the point of prepend communities?
> On Oct 26, 2017, at 2:37 PM, William Herrin <bill at 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.
More information about the NANOG