From: Nick Shah (nshah@xxxxxxxxxxxxxx)
Date: Sat Jun 01 2002 - 20:59:11 GMT-3
Nigel/Howard,
Thanks for your answers/insights.
No, this scenario is *not* a practical scenario, I havent even come across
it anywhere. There isnt anything in particular that I am trying to acheive
here, except trying to know "how many ways to change a light bulb" thats
all.
I am sorry, if my excuse doesnt amuse you. I think Advertise-map, etc.
feature is a relatively new one, which made me think if I could acheive it
in some other way, and hence the Question.
Nigel, thanks for you answer. I will lab it up and check (prima facie, it
seems that it will succeed).
rgds
Nick
-----Original Message-----
From: Nigel Taylor <nigel_taylor@hotmail.com>
To: ccielab@groupstudy.com <ccielab@groupstudy.com>
Date: Sunday, 2 June 2002 9:23
Subject: Re: BGP conditional Advertisement
>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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