BGP Path Filtering

Iljitsch van Beijnum iljitsch at
Sat May 17 18:59:59 UTC 2003

On zaterdag, mei 17, 2003, at 17:30 Europe/Amsterdam, Joe Abley wrote:

>  think that the message "community strings are hard" (like its friends 
> "BGP is hard" and "let's turn on RIP") need to stop propagating. It is 
> just not that difficult to do things right the first time, and you 
> don't need to be a bigger network than a pair of 2501s with a small 
> handful of external BGP sessions to see the benefit of it.

You are saying BGP isn't hard when well-informed people can't even 
agree on a way to disable unwanted default behavior? Hm...

Filtering AS paths and prefixes is relatively well understood, although 
I hear lots of people fail the CCIE questions on AS path regular 
expressions. I wouldn't recommend doing it with communities to people 
who don't have any experience with route maps. And I don't see the 
point for people who don't have BGP-speaking customers. Apart from that 
it's mostly a change management issue. The communities mechanism has 
the advantage you only have to make changes on the routers where the 
prefixes enter the network (presumably a single customer-facing router) 
while explicit filters must be updated on all eBGP routers.

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