URPF on small BGP-enabled customers?

Fri Jun 3 20:50:32 UTC 2005

Pete Templin wrote:
> 
> will at loopfree.net wrote:
> 
>> This is new to me, but I haven't bought any new transit in the past 18 
>> months -- is
>> this common practice on multihomed BGP customers now? I could force 
>> things to work
>> by always advertising all my prefixes out to them with the obvious 
>> downside of
>> living in fear of my outbound traffic being dropped if I ever need to 
>> withdraw any
>> of them.
> 
> 
> I (a network much, much smaller than Sprint) do uRPF on all ports, but 
> also inform BGP customers (nine-page handoff documentation) that they 
> are uRPFed.  However, in conjunction with community support for 
> adjusting localpref, we set a sufficient weight on the announcement so 
> that the edge node sees the customer link as preferred even if the rest 
> of our network doesn't, and therefore the uRPF check passes.

This sounds like the better approach. Although this is still not 
strictly what the customer want, because all peers of the same edge will 
prefer the edges path.

> 
> I don't think advertising more-specifics through other connections would 
> actually work, as the Sprint edge router would still want to reach the 
> more-specifics through the Sprint network, rather than the customer 
> link.  It's all a matter of what the FIB says.
> 
> pt
> 
> 