[c-nsp] BGP conditional export

[Bruce Pinsky]

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Dean Smith wrote:
> 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
> 
> 

He could also probably do something with TCL scripting to monitor the total
number of routes being received from Neighbor A and if it drops below the
threshold, bring up his Neighbor B connection or change the route-map and
do a soft reset of the peer.

- --
=========
bep

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