Alternate default route

dbouthillier · ‎01-30-2007

I have a remote office that is connected to the data center via a point to point T1. We had a DSL Internet connection installed at the remote office last week for Internet bound traffic. The T1 router is the default gateway for the remote office. I added the following static route on the T1 router, to direct all Internet traffic to the DSL router/gateway, and traffic went out the DSL to the Internet fine.

ip route 0.0.0.0 0.0.0.0 192.168.1.1

I added an administrative cost of five to the static route and another static route with a higher administrative cost as a backkup. I would like to send Internet traffic across the T1 if the DSL goes down.

ip route 0.0.0.0 0.0.0.0 192.168.1.1 5

ip route 0.0.0.0 0.0.0.0 10.1.1.1 254

They are still able to connect to the Internet via the DSL router/gateway, however if we unplug the cable going to the DSL router, Internet bound traffic is not routed across the T1.

What am I doing wrong?

Thanks,

Daris

vijayasankar · ‎01-30-2007

Hi Daris,

This is a classical problem with static routes.

I hope your DSL router 192.168.1.1 is connected in your LAN. and your T1 Router is also connected in this LAN.

If so, Even When the DSL router goes down, the T1 router will not discover that the DSL router has gone down. Because The ethernet interface on your T1 Router is up, so the T1 Router will think it can reach 192.168.1.1.

This will work, if you unplug the ethernet cable on your T1 Router. The reason is clear. When you do this, the T1 router has no route to reach the 192.168.1.x segment, so that static route will be removed from the routing table, and your next default static route will take effect.

To overcome this situation, you need to use a feature called "Reliable static routes using object tracking".

By Using this feature, you configure the router to periodicaly monitor a destination IP to gather statistics. You can tie this monitoring process to the static route and configure such that when the destination ip is not reachable, the corresponding static route will be removed from the routing table.

Have a look at this URL, to know more on this feature.

http://www.cisco.com/en/US/products/sw/iosswrel/ps5413/products_feature_guide09186a00801d862d.html

Hope this helps.

-VJ

vijayasankar · ‎01-30-2007

Hi,

Have a look at this recent thread for yet another good example from "Martin Heusinger" on this topic

http://forum.cisco.com/eforum/servlet/NetProf?page=netprof&forum=Network%20Infrastructure&topic=LAN%2C%20Switching%20and%20Routing&CommCmd=MB%3Fcmd%3Dpass_through%26location%3Doutline%40%5E1%40%40.1ddd66fc/0#selected_message

-VJ