This is a bit of an interesting one, the brief is to provide Internet connectivity from two sites, A and B. There is also a point to point LES link between the two sites to provide intersite connectivity, there is also a wireless point to point link as a backup for the LES link. Between the two site core switches an EIGRP area will run so that if the main intersite LES link goes down, it will failover to the wireless point to point automatically. Each site has its own local Internet connection that will be used by that sites clients in normal operation. In the event of a local internet link failure, the default route should adjust automatically to push the Internet traffic out of the other site (via the inter-site link.)  I'm only going to show the juicy bits of the config. I.e. the bits that refer to the routing, EIGRP or IP SLA stuff. A user at Site A in normal use should see two default routes to the Internet, one being their local default route, and then the Site B default route, with a higher metric (because its come across the EIGRP network.) If Site A's Internet connection goes down, the IP SLA removes the track 1 route, i.e. the default route. This leaves only the site B default route, that then even though it has the higher metric is the only route available so it is then used. If both Internet connections go down at the same time, both routes disappear. The route-map is there to force the IP SLA tracking connection out of only the local internet connection. If you did not have this, in the event of a failure, the route would be removed because the IP SLA would see it had gone, but then it would continue to track via the internet connection at site B. Oh dear, it would then find the tracked IP address available again via Site B's internet connection and put the route back in. At which point it would see it was down and remove the route. At which point you are now in "flap-city" and it will continue to flap back and forth. So putting the route-map forces the connection out the local only, meaning if the Internet connection goes down. It goes down hard and stays down, until the connection is repaired at which point it comes back in. Site A
Site B
Site C (i.e. the switch half way along the point to point wireless)
Debugging and Testing # debug ip sla (monitor) error IP SLAs ERROR debugging for all operations is on # debug track # debug ip routing IP routing debugging is on And then turn on “terminal monitor” you’ll now be able to track any of the messages created by these sub-systems. |
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