[c-nsp] BGP conditional export

[Dean Smith]

I don't know your specifics but we have a specific case where we need to:-

Advertise to Neighbor A under "normal" circumstances
Under certain conditions, withdraw advertisments from A and advertise via
neighbor B.

The particular conditions wern't supported by BGP Conditional Advertisment
http://www.cisco.com/en/US/tech/tk365/technologies_configuration_example0918
6a0080094309.shtml

So (1) we used "advanced object tracking" to create objects that tracked the
conditions:-

Presence of Route X
Presence of Route Y
Reachability of Host Z 
Etc etc.

(2) We then used another object to track the combined state via a boolean
expression.

(3) That last object was used to conditionally advertise static routes
corresponding to the various summaries we wished to advertise with varying
tags/metrics.

(4) Route maps for Static to BGP redistribution were used to match the
tags/metrics of the active static routes and convert to BGP communities

(5) Finally the various eBGP neighbor route-maps advertise (or not) based on
those BGP communities.

It actually works very well and served our purpose. Annoyingly we had to add
a 2800 to run the advanced object tracking part because 6500s cant (Who
knows why Cisco don't think the top of the range enterprise DC switch
doesn't need object tracking??)

Object tracking can track some routing protocol metrics against thresholds
but not BGP so I don't know if this will fit your needs.
http://www.cisco.com/en/US/products/ps6350/products_configuration_guide_chap
ter09186a008042fbeb.html


Dean


-----Original Message-----
From: cisco-nsp-bounces at puck.nether.net
[mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of Adrian M
Sent: 05 February 2007 20:48
To: cisco-nsp at puck.nether.net
Subject: [c-nsp] BGP conditional export

Is there a way to condition BGP prefixes export to a neighbor B when the
prefixes received from neighbor A is bellow a threshold ?
I try to use neighbor B for backup only and to export my prefixes only when
something is wrong with neighbor A.

Is such thing possible ?

--
Best regards,
Adrian Minta
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