[c-nsp] as-override

[Dean Smith]

This scenario may be unusual in the ISP world where genuine AS 
re-use/overlaps are very rare but is much more common in the Enterprise 
world and I've faced it myself. e.g. I had to intregrate 2 disparate 
networks who both used an MPLS service from the same WAN provider.

As such the route tables on both networks had  <Private AS>.<SP MPLS 
AS>.<Private AS> paths and a full dynamic exchange fell foul of the 
anti-looping. The SP didn't (and wouldn't) provide any of the SP based 
options (allow-as-in etc.) to get round it.

In the end I had to dump all the routes from one network into an igp and 
then redistribute "clean" routes iback into BGP. Complexity and extra boxes 
I could have done without. Whilst the ability to remove specific AS numbers 
from an as-path might be perceived as undesirable or dangerous on the 
internet - it would have made many an enterprise engineer's life very much 
easier. Its not like there aren't other configuration options which can be 
equally dangerous in the wrong hands.

Dean Smith

----- Original Message ----- 
From: "Gary Roberton" <gary.ciscomail at gmail.com>
To: "Peter Rathlev" <peter at rathlev.dk>
Cc: <cisco-nsp at puck.nether.net>
Sent: Monday, April 14, 2008 10:25 AM
Subject: Re: [c-nsp] as-override


> Peter
>
> Thanks for your reply.  Why can't Cisco put it as simply as that.
>
> I am only trying to replace the AS as the one being advertised by R1 is 
> used
> again by another part of the network.  i.e. R5 also uses the same AS
> number.  I need my network to be advertised through to R5 and R5 would 
> drop
> the updates if it saw its own AS number inthe path, therefore I am trying 
> to
> find various options to 'hide' the AS of R1.  This was one of the 
> potential
> options but not now as it doesnt do what I want it to do.
>
> Hope this makes sense.
>
> Gary