[c-nsp] Remove BGP AS path number number from an AS PATH

[Dean Smith]

This list does tend to focus on public internet issues and forget that BGP
is used in corporate or other "non-internet" environments that don't follow
nice conventions and after 15+ years of corporate take-overs,mergers and
demergers can often find situations where AS Paths need to be "cleaned"or
manipulated with something more flexible than a straight pre-pend. IOS
allows every other key BGP metric to be tweaked and we accept the risks that
brings - so this sort of manipulation of the AS-Path is long overdue.

Examples where I have had to dump BGP routes into an IGP for a hop and stick
them back into BGP with a "clean" AS-Path. :-

A) 2 independant organisations both use MPLS VPN from the same provider and
want to exchange routes across a private peering. The MPLS provider AS is in
the AS-Path on both sides and the provider drops routes. The provider
doesn't offer any of the provider side workarounds. 

B) 1 Organisation that has historically been a fully private network and has
some historic peerings that use non-private AS/non-registered AS now wants
to have a private peering with "a proper" public network. The AS-Path needs
to have the "junk" removed before the routes could be advertised. Yes the
historic networks should be migrated away but the fact is there is often no
resource and no money to do that when the workaround is simply another
Router.

C) Organisation wants to Dual Home to 2 ISPs at 2 locations for a new
internet service. It wants to use its private network for backhaul between
the sites but can't have free flow of routes between because if they
traverse the MPLS VPN they get the provider AS inserted in the path.

I don't intend to debate the above....they happened and the solutions were
ratified by Cisco but in all cases manipulating the AS-Path (usually to
remove the MPLS provider public AS) would have been much much easier than
the final solutions. 

The summary is...BGP isn't just used on the Internet, and corporate networks
get messy when CEOs get ambitious (or fired).

Dean

-----Original Message-----
From: cisco-nsp-bounces at puck.nether.net
[mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of
masood at nexlinx.net.pk
Sent: 28 May 2009 17:56
To: Varaillon Jean Christophe
Cc: cisco-nsp at puck.nether.net
Subject: Re: [c-nsp] Remove BGP AS path number number from an AS PATH

yup, you can't remove public AS from AS path. would you please share the
idea why you wana remove it :)

there are many other attributes to tweak bgp, y not u use them.

BR\\
Masood


> I doubt that you can do that... but if this is to influence your outgoing
> traffic, then I would use local-preferences.
>
> Christophe
>
>
> -----Original Message-----
> From: cisco-nsp-bounces at puck.nether.net
> [mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of Michalis Palis
> Sent: Thursday, May 28, 2009 9:49 AM
> To: cisco-nsp at puck.nether.net
> Subject: [c-nsp] Remove BGP AS path number number from an AS PATH
>
> Hello All
>
> Is their a way to remove the first AS number (not private) from an AS
> path?
>
> For example we are receiving a route with AS PATH  123 456 456 456 and we
> want to remove the 123 AS and put in the BGP table the route with AS 456
> 456
> 456 .
>
> Thanks for your reply
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