IP SLA with PBR

[Denny Trujillo]

Let's say I have two routers (A and B) each with their own ISP connection, with router A acting as the default gateway for the internal network. I want to configure policy based routing on router A to send traffic from specific internal sources out router B. However, I only want this to happen if router B is reachable. I know I can configure IP SLA on router A to track the reachability of router B, but I need to also track if router B has access to the internet using it's own ISP. I don't want router A sending traffic to router B if router B can't reach the internet. I'm not even sure if such tracking is possible. Thanks for the help.

[Reza Sharifi]

You can try that if router A and B are running BGP with the service provides and also they are connected together using IBGP.

Have a look at this link for example and configs:

http://www.cisco.com/en/US/tech/tk365/technologies_configuration_example09186a00800945bf.shtml#conf5

HTH

[Denny Trujillo]

Each router is running BGP with their ISPs and iBGP is running between them. I want to make as much use as possible of both ISPs, at least form a downstream perspective. This is a college network and students download like no other. I'm sending certian traffic to router B, then natting a second time at router B so that the return traffic comes back the same path (the ISP on router B). This allows me to make full downstream use of the ISP on router A and B. Again, my only issue is that I don't want to send traffic to router B if router B can't access the internet using it's own ISP.

[Richard Burts]

I have not done anything quite like this but I think that it should be possible. My suggestion would be to approach it in this way:

- pick some resource in the Internet (probably one that is not very important to you).

- on router A configure a static route for that resource that sends it to router B to get to the Internet.

- configure PBR using the verify availability/IP SLA to check the resource that is reached through router B. If that destination is reachable you have proved that router B is working and has Internet reachability.

HTH

Rick

[sajid_m123]

-you can configure a dummy static route on routerB to null0 while tracking object with ipIcmpEcho pinging ISP side address and using source IP connected to ISP. If ping from source to ISP is successfull then this route would go into routing table.

"ip route x.x.x.x 255.255.255.255 Null0 track 10"

"track 10 rtr 5 reachability"

- Redistribute this static route to the core router (maybe routerA in this case)

- Configure policy based routing on routerA with option "set ip next-hop verify-availability 10 track 20"

& track 20 ip route reachability