I've converted a T1 connection between two sites to use multilink PPP, in preparation for putting in a second T1 between the sites. As part of this change I moved the IP address (172.29.1.25, with a /30 netmask) from the serial line (serial1/0) to the multilink interface (multilink1).
This caused a change in the routing table that I didn't expect. Before the multilink config, the relevant routing table entries looked like this:
172.29.0.0/30 is subnetted, 9 subnets C 172.29.1.24 is directly connected, Serial1/0
The other 8 subnets on 172.29.0.0 were also /30s. But after the switching to the multilink the routing table now looks like this:
172.29.0.0/16 is variably subnetted, 10 subnets, 2 masks C 172.29.1.24/30 is directly connected, Multilink1 C 172.29.1.26/32 is directly connected, Multilink1
So apparently what's happening is that not only is the route for the network on the multilink interface itself being added to the routing table (as I expected), but also another route for the IP address of the router on the *other side* of the multilink interface (172.29.1.26).
Is this expected behavior? This is on IOS 12.3(17a), by the way. If it's not expected behavior, any ideas why it would be happening?
- John