traffic for network of ip next hop goes down

[apkothiyal]

we are using two rtrs RTR-A and RTR-B, both are cisco 7604. RTR-A is connected one ISP and RTR-B is connected to another ISB. Both rtrs are running BGP with their ISP peer. Some of the networks of RTR-A are configured as ip next hop to RTR-B.

The problem is when ISP LINK of RTR-A goes down the traffic of networks of RTR-A also went down for which next hop is configured RTR-B
Can some one explain why?

[Calin C.]

Hello,

Between RTR-A and RTR-B, what routing protocol do you have?

Next questions:

"Some of the networks of RTR-A are configured as ip next hop to RTR-B"

What networks are these? External networks? How is the next hop configured? Static routing?

I understand your problem, but the explanation need some clarification.

Thanks,

Calin

[apkothiyal]

RTR-A and RTR-B is connected back to back. Internal Network of RTR-A is configured ip next hop as RTR-B interface ip connected to RTR-A,

ip policy route-map next_hop    on interface

route-map next_hop permit 20

match ip address 101

set ip next-hop ip x.x.x.x (ip of interface of RTR-B connected to RTR-A)

[Rick Morris]

One thing that needs to be checked is the route advertisements to the ISP?

If you have routes you need advertised for routing back in case one link goes down then you need to make sure the routes are being sent out in the first place.  If one link goes down and that is the only link advertising that route then it will never be routed since the routes are removed from the BGP table and then the routing table.

Another possible answer is the IP blocks are too small to be routed beyond the ISP you are connected to.

What are you trying to accomplish?

Do you have your AS and IP space?

Are you receiving any BGP routes from the ISP?

With the route-map it sounds like you are using PBR's and static routes.

[apkothiyal]

Thanks for reply.

I have just plotted the diag. The b.b.b.b/24 pool is routed to rtrb using next hop commend. it is advertised through ISP-B.

The issue is that when ISP -A link goes down the traffic of b.b.b.b pool also goes down.while ISP-B link is up.

[Rick Morris]

What is behind the routers, are they 2 separate switches or one?

With what you are doing I would set up HSRP groups, this way you can route out either in case of outage.

Have a.a.a.a/24 on Router A as one group primary and a.a.a.a/24 on Router B as back-up

Have b.b.b.b/24 on Router B as another group primary and b.b.b.b/24 on Router A as back-up

Have c.c.c.c/24 on Router B as another group primary and c.c.c.c/24 on Router A as back-up

This will give you want you want and will also provide failover in the event of an outage.

The other way to accomplish this is to get rid of the route-map and just use static routes.  As long as your next hop is accessible your route will not be removed from the routing table.

To see why the routes are being removed when the link goes down we need to see where the route-map you created is applied.