I have two sites connected via a Point to Point T1 link. In each side of the point to point link I have two different subnets (i.e. 192.168.2.0 and 192.168.3.0). I have a a full copy of each other on each side of the link (just in case it goes down). At both ends of the PTP link I have a cisco router. I understand that If I have both the serial and the ethernet interfaces plugged in at the same time, the router will always use the Ethernet interface, because it is a directly connected network. Can I still set it up with two paths to the same place (ethernet and serial) and leave the ethernet connection disconnected until it needs to be up? In other words, my serial link goes down, so I plug in my ethernet interface to the standby network and bring it up.
If it is directly connected network, then you cannot force the router to
send the traffic over T1 link. What I was suggesting is possible if the
router is routing over Ethernet link as well (Ethernet link should have
address other than 192.168.x.x address).