[c-nsp] BGP blackholling with communites

[David Freedman]

Gert Doering wrote:
> Hi,
> 
> On Mon, Mar 21, 2005 at 11:17:13AM +0000, David Freedman wrote:
>> I had assumed that it would bypass the "next-hop-self" action which may
>> be applied to the peering router's iBGP peers (countering the ability to
>> propogate the new next-hop around the network), there are some mixed
>> opinions about whether this should or should not work to do this,
>> (whether it actually works and is implemented is another matter!)
> 
> "Origin" has no influence on "next-hop-self" - it's only an attribute that
> will be used as a tie-breaker somewhere low in the BGP decision hierarchy.
> 
Sure, but I would have hoped that cisco would have used some attribute 
(this being the most sensible one) to decide on how to implement 
next-hop-self.

> So if you use next-hop-self, you'll need to do it via route-map and exclude
> prefixes carrying the blackhole community.
> 
not nice at all :(

> Oli - this is an important point indeed.  How do other networks handle this?
> 
>> however its nice to have a determined "origin" attribute anyway :)
> 
> As the route is coming in from a customer, overriding the "origin" attribute
> that they send to you might not be what they want...
> 
Well, allthough ORIGIN is a well-known mandatory attribute, I don't see 
any point in anybody external setting it, I'm quite happy to reset it on 
the edge.

Dave.




> gert