From: Nigel Taylor (nigel_taylor@xxxxxxxxxxx)
Date: Sat Jun 01 2002 - 19:44:49 GMT-3
Nick,
I understand what it is you're trying to accomplish by trying to
find another way to perform BGP conditional route advertising.
However, as Howard points out the question would be why? I've looked at the
scenario you've posted and based on the information
you provided, I don't see how we can get the BGP process in RtrC to
conditionally source the Y/24 network, without some type of
tracking of routes in the BGP table. You mentioned the goal is to
accomplish this without specifically using the
"advertise-map & non-exist-map" neighbor command. The only other options
left would be using filter-list, distribute-list, and route-maps
which would be static configurations.
I did some thinking and it came to me that maybe the only other way I could
think of to accomplish this would be to, identify the X/24 route being
received from RtrA at RtrC using a route-map and setting a community string
on the X/24 route. Then under the bgp process of RtrC you could
use the "network" command with a "route-map" to set another community string
for the Y/24 route. Lastly you could set and outbound route-map
to RtrB(on RtrC) using the 'no-advertise" attribute to filter the Y/24 route
based on if the X/24(community) route is present or not.
Nigel
----- Original Message -----
From: "Howard C. Berkowitz" <hcb@gettcomm.com>
To: <ccielab@groupstudy.com>
Sent: Saturday, June 01, 2002 2:54 PM
Subject: Re: BGP conditional Advertisement
> At 7:08 PM +1000 6/1/02, Nick Shah wrote:
> >Nigel,
> >
> >All routers are running in different AS's
> >
> >No IGP's running between all of the 3 routers.
> >
> >X/24 is being originated from RtrA
> >y/24 is to be *conditionally * originated by RtrC (if RtrC stops
receiving
> >X/24 from RtrA)
>
> I, too, don't quite have enough detail to give a definitive answer,
> particularly as to where y/24 is and how router C knows about it.
>
> What is the address relationship between x and y? What problem are
> you trying to solve? This doesn't seem a plausible backup scenario,
> unless y is an alternate address that will be tried in recovery by a
> host connected to rtrB.
>
> Approaches that might be considered include making the next hop in C
> for y primarily dependent on the reachability of a next hop in A.
> Another approach might be to use outbound route filtering in B to C,
> in which B tells C not to advertise y as long as it is receiving x
> originated by A.
>
> >
> >thanks
> >Nick
> >-----Original Message-----
> >From: Nigel Taylor <nigel_taylor@hotmail.com>
> >To: ccielab@groupstudy.com <ccielab@groupstudy.com>
> >Date: Saturday, 1 June 2002 3:43
> >Subject: Re: BGP conditional Advertisement
> >
> >
> >>Nick,
> >> I have a couple of questions?
> >>
> >>1. What AS's are the 3 routers in? could you be more specific.
> >>2. The X and Y routes where do they originate? both from RtrA, X from
> >RtrA,
> >>Y from RtrC?
> >>3. Are there any IGPs running between all the routers.
> >>
> >>Nigel
> >>
> >>----- Original Message -----
> >>From: "Nick Shah" <nshah@connect.com.au>
> >>To: <ccielab@groupstudy.com>
> >>Sent: Friday, May 31, 2002 11:11 PM
> >>Subject: BGP conditional Advertisement
> >>
> >>
> >>> Guys,
> >>>
> >>> I am trying to achieve a behaviour similar to BGP conditional
> >>advertisement
> >>> *without* using non-exist-map and/or advertise-map. Basically ...
> >>>
> >>> RtrA ------- RtrC-----------RtrB
> >>>
> >>> RtrA advertises route X/24 to RtrC under normal circumstances, when
RtrC
> >>is
> >>> receiving X/24 from RtrA it suppresses the advertisement of Y/24
(doesnt
> >>> advertise) to RtrB.
> >>> But if RtrA stops sending prefix X/24 to RtrC, RtrC starts sending
Y/24
> >to
> >>> RtrB.
> >>>
> >>> All this to be done *without* using advertise-map & non-exist-map
> >>>
> >>> Ideas..
> >>> Nick
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