From: Hossam (sam6626@yahoo.com)
Date: Sun Feb 01 2004 - 20:03:56 GMT-3
Hi Brian,
Thanks a lot for you post. I missed u lately.
^(\(.*\))?$
Waaw...what an Irregular expression:)
i would read it as follows...(correct me if read it mistakenly)
all as-paths that starts with ( and includes anything and ends with ) and repeated ONE or more times!!!
I think it is typically what i need.
But i got this expressoin form the group too. I think it looks simpler. and i guess that it does the same function.
^$ | \)$
^$ = local originated
\)$= in any other subAS
what is yr opnion?
Thanks
SAM
From: "Brian McGahan" <bmcgahan@internetworkexpert.com> Add to Address Book
To: "'Bob Sinclair'" <bsin@cox.net>, "'Hossam'" <sam6626@yahoo.com>, ccielab@groupstudy.com
Subject: RE: AS-Path Filtering with BGP Confiderations!
Date: Sun, 1 Feb 2004 15:59:28 -0500
I'm not sure how you would keep some routers inside your AS
confederated and some not... instead what you need is an expression
that
will match locally originated routes as well as those from your
confederation peers. This will do the trick:
^(\(.*\))?$
HTH,
Brian McGahan, CCIE #8593
bmcgahan@internetworkexpert.com
Internetwork Expert, Inc.
http://www.InternetworkExpert.com
Toll Free: 877-224-8987
Direct: 708-362-1418 (Outside the US and Canada)
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
Of
> Bob Sinclair
> Sent: Saturday, January 31, 2004 5:16 PM
> To: Hossam; ccielab@groupstudy.com
> Subject: Re: AS-Path Filtering with BGP Confiderations!
>
> Sam,
>
> I can confirm that your AS 200 will not show up within the sub-ASs.
So if
> you do sho ip b reg ^$ you will see routes from the local sub-as, not
> routes
> from AS 200.
>
> To do an as-path filter that will send only routes from within AS
200, you
> would have to include the empty path, ^$, as well as all other
sub-ASs.
>
> This is quite inconvenient! For just this reason, perhaps it would
be
> desirable in a real-world implementation to keep your AS border
routers
> out
> of your confederations. That way you can easily permit ^$ to allow
only
> your own routes outbound.
>
> HTH,
>
> Bob Sinclair
> CCIE #10427, CISSP, MCSE
> www.netmasterclass.net
>
> ----- Original Message -----
> From: "Hossam" <sam6626@yahoo.com>
> To: <ccielab@groupstudy.com>
> Sent: Saturday, January 31, 2004 5:41 AM
> Subject: AS-Path Filtering with BGP Confiderations!
>
>
> > I am trying to configure a BGP router R2 in (AS 65 256 and Bgp
> Confideration indentifier 200) to limit it advertesment to its EBGP
> neighbour (R4 in AS 300) to the routes that was originated in AS 200.
> >
> > I noticed that while i am AS-path filtering (either via filter-list
or a
> route map) and an ip as-path accesslist that permits only ^200$,
nothing
> gets advertised to the neighbour R4.
> >
> > Once i remove the as-path filtering i get the routes with AS-path =
200
> at
> R4 as expected.
> >
> > I think the problem is that R2 has the routes with AS-path =
(65078)
> cause
> of the confidertaions in its BGP table.
> > It seems that the IOS does the filtering first and then it strips
of the
> confiderations as-path just before advertesting the routes to EBGP
> neighbour.
> >
> > Now the question is: what is the best way to do the filtering in
this
> case? i hate the idea of filtering on the SUB ASs...any ideas...
> >
> > Thanks..
> > SAM
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