NAT BOUNDARY

sectelj
sectelj used Ask the Experts™
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Route (200.0.0.1/32) is advertised by BGP over multiple AS's to a router that NAT's (200.0.0.1 - 20.0.0.1).   Now 2.0.0.1 is converted to a static route to null0 and advertised into BGP.  ONLY THE NEW ROUTE  -2.0.0.1- is allowed to propagate.  All other routes behind the NAT boundary are filtered.

#ip route 2.0.0.1/32 null0
#router bgp 1200
#network 2.0.0.1 mask 255.255.255.255

The problem:

The new route (2.0.0.1)  has no knowledge of the original route (200.0.0.1)

Is there any method such as IP SLA, specialized route maps or specialized TCL programs that would modify or remove the new route (2.0.0.1) should an issue occur on the originating network that would prevent the original route of 200.0.0.1 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 2.0.0.1 route.

Remember.... the issue is the fact that the original route 200.0.0.1 is not allowed to propagate beyond the NAT boundary due to route filtering and instead only the new NAT induced route (2.0.0.1/32) 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///
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Network Architect
Commented:
Is the 200.0.0.1 route present in the routing table of the NAT router? If so, you can use an "track 200 ip reachability 200.0.0.1 255.255.255.255 reachability" statement and then alter your null route to be present only when the track is up.

Author

Commented:
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

Commented:
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.

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