Re: What's the point of prepend communities?

[Mike Hammett <nanog () ics-il net>]

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.