From: Godswill Oletu (oletu@inbox.lv)
Date: Tue Jun 06 2006 - 22:45:02 ART
Navin,
I see this as a 'stupid router strick', the comment 'do not use the remove
private-as option' is just a diversionary tactics to throw one off balance.
By default, if a BGP router aggregates a particular prefix, it originates
that prefix from its own AS and will stripe off all the the ASes the routes
might have passed through before geting to it.
A simple three router test, will show you what is happening:
(R7)AS65001------------(R1)AS300-------------------BB(AS400).
Configure all three BGPs as eBGP neighbors and originate something like
55.55.55.0/24 on AS65001, most likely a looback interface on R7.
On R1, the as-path will be"65001" on BB the as-path will be "300 65001".
Now, go to R1 and aggregate/summary-only 55.55.55.0/24 to something like
55.55.54.0/23. Go back to BB, you will notice that, the as-path will change
to "300", telling you that the route was originated on AS300 and at the same
time solving the "problem" of removing the private-as, without using the
'remove private-as option.
HTH
Godswill Oletu
----- Original Message -----
From: "Navin MS" <navin_ms07@yahoo.com>
To: "gregg malcolm" <greggmalcolm@yahoo.com>; "Godswill Oletu"
<oletu@inbox.lv>; <ccielab@groupstudy.com>
Sent: Tuesday, June 06, 2006 1:41 PM
Subject: Re: Filtering Private AS using Regexp ?
> Hi Gregg,
>
> The scenario is that AS 300 has peered with two other ASes, 65001 and
65002. Note that all the
> three are independent Autonomous systems. AS 300 is aggregating all the
routes from AS 65001 and
> 65002 and is sending to a Backbone service provider.
>
> Therefore, AS 300 should remove these private ASes from the routes before
sending it out to the
> service provider and the catch is not to use the "remote-private-as"
option.
>
> I could match these private ASes using a regexp "_[64512-65535]_" (which
means if the AS path
> contains any private AS numbers), but then how do I filter that ?
>
> IOS lets us either "append an AS" or "remote-private-as" when sending
routes to the neighbor. But
> there is no way to selectively remove some ASes from the AS path !! If
there is a way to do this,
> then this problem is solved.
>
> Thanks.
> Naveen.
>
>
>
> --- gregg malcolm <greggmalcolm@yahoo.com> wrote:
>
> > How about a BGP confederation?
> >
> > Gregg
> >
> > Godswill Oletu <oletu@inbox.lv> wrote: Naveen,
> >
> > Try the 'neighbor 1.1.1.1 local-as xxx no-prepend' command and see if it
> > will work for you.
> >
> > Thanks.
> > Godswill Oletu
> >
> > ----- Original Message -----
> > From: "Navin MS"
> > To:
> > Sent: Friday, June 02, 2006 10:17 PM
> > Subject: Filtering Private AS using Regexp ?
> >
> >
> > > Hello Group,
> > >
> > > While trying to filter Private-AS numbers, we know we can use the
neighbor
> > > statement with
> > > "remove-private-as" option.
> > >
> > > Is there an alternate way to do this, without using the above option ?
> > >
> > > I'm thinking of using a regexp to match private AS numbers... but
wasn't
> > > successful. Any idea ?
> > >
> > > TIA,
> > > Naveen.
> > >
> > > __________________________________________________
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> > >
This archive was generated by hypermail 2.1.4 : Sat Jul 01 2006 - 07:57:32 ART