We are using 3750G switches to route traffic through our Metro Ethernet network. We have a hub and spoke topology but a few of our sites have secondary links to other sites for redundancy. The physical switch ports are all setup as layer 2 trunk links and we emplement layer 3 using vlan interfaces. We are also using EIGRP for routing. The default-route on each 3750G points back to the hub via the VLAN 21 interface.
Now here is my problem. We setup secondary links between some of the sites for redundancy so that traffic can get back to the hub in case the main link goes down at that site. When the actual physical Metro E link goes down I am finding that traffic for unknown networks are not being routed.
If I do a trace route the packets never leave the originating L3 switch. If I take down the physical link "and" shutdown the corresponding vlan interface the default route traffic will then go out the backup link.
What I need to figure out is how to get it to failover to the backup link when the physical link to Metro E goes down. Does anyone have any ideas that I can try?
The issue that you describe about not failing over to a secondary default route is fairly common when using static default routes. But your description indicates that you are using EIGRP for routing. EIGRP is usually quite good about detecting failed links and switching to a secondary path. Do you perhaps have static default routes configured in the spoke switches?
If you do have static default routes then I would suggest that the optimum solution would be to remove the static default routes and to let EIGRP advertise the default route.
If you do not want to give up the static default route then there is a feature i IOS for Reliable Static Routing Backup Using Object Tracking. This link will give some information about it:
If you're using the default-route by hard-coding it on each spoke device (e.g. ip route 0.0.0.0 0.0.0.0 x.x.x.x), you might consider advertising it within EIGRP from your hub instead. Another option might be the usage of enhanced object tracking to track the next upstream device. (Unsure how much of this feature the 3750 offers.)