[c-nsp] Setting "weight 255" as default for customer BGP with uRPF strict

[Brian Feeny]

Pete,

Ok, let me clarify, the customer is dual homed to a single ISP.  
routers A and B both belong to the same ISP.

You can have the same "problem" though when multi-homed to two 
different ISP's, because then the customer will announce say a /24 and 
its aggregate /20 to ISPA and a different /24 and its aggregate to 
ISPB.  ISPA will see the more specific /24 from ISPB, and put an entry 
in its FIB for its egress interface.  Yet its still possible the 
customer sends traffic to ISPA on its ingress interface......which uRPF 
would  drop unless something such as weight was being set on the 
neighbor.

brian

On Nov 21, 2004, at 8:19 PM, Pete Templin wrote:

> Brian Feeny wrote:
>
>> Customer Router C connects to your Router A and  your Router B.
>> Customer sets localpref to 100 on network A to router A, and 70 on 
>> network B to router A
>> Customer sets localpref to 100 on network B to router B, and 70 on 
>> network A to router B
>
> Customer connects to OtherNetworkG, and announces longer specifics of 
> networks A and B to OtherNetworkG.  Routers A and B learn these longer 
> prefixes, and their FIBs no longer point to Router C.  Most specific 
> announcement is a bigger hammer than weight, so strict mode backfires.
>
> pt