sectelj used Ask the Experts™
Route ( is advertised by BGP over multiple AS's to a router that NAT's ( -   Now is converted to a static route to null0 and advertised into BGP.  ONLY THE NEW ROUTE  - is allowed to propagate.  All other routes behind the NAT boundary are filtered.

#ip route null0
#router bgp 1200
#network mask

The problem:

The new route (  has no knowledge of the original route (

Is there any method such as IP SLA, specialized route maps or specialized TCL programs that would modify or remove the new route ( should an issue occur on the originating network that would prevent the original route of from making it to the NAT boundary.  

I would be interested in any mechanism that can confirm the health of the old route and when required block or modify the attributes of the new route.

Remember.... the issue is the fact that the original route is not allowed to propagate beyond the NAT boundary due to route filtering and instead only the new NAT induced route ( is advertised beyond the NAT boundary.  I am seeking some method of TRACKING the health of the original route or connectivity to the originating router so that should and issue occur then the new route would be modified.

Yes....this is a very challenging scenario///
Watch Question

Do more with

Expert Office
EXPERT OFFICE® is a registered trademark of EXPERTS EXCHANGE®
Network Architect
Is the route present in the routing table of the NAT router? If so, you can use an "track 200 ip reachability reachability" statement and then alter your null route to be present only when the track is up.


Not bad  but the real solution is to use an "advertise map"//this does the job.

If route A does not in the routing table then the new route will not be advertised
Jody LemoineNetwork Architect

Either works. Advertise map is used if you don't want the local routing table to be affected and only want to control what is sent to remote peers. Tracked routes directly affect the local routing table •and• what is advertised to peers by redistribution of the static routes.

Do more with

Expert Office
Submit tech questions to Ask the Experts™ at any time to receive solutions, advice, and new ideas from leading industry professionals.

Start 7-Day Free Trial