URPF on small BGP-enabled customers?

Fri Jun 3 14:13:26 UTC 2005

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.

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