I've run into an error that appears to be a very basic misunderstanding on my part. I have a 3620 with several subinterfaces running frame-relay point to point. Each subinterface has a unique 192.168.X.1 255.255.255.0 address. In an attempt to segment an existing network, I wanted to simply change a subinterface's IP address of 192.168.20.1 255.255.255.0 to 192.168.20.1 255.255.255.252, giving me 20.1 to static route to 20.2 at the remote end. The router gives me a "Bad mask /30 for address 192.168.20.1" error when I attempt to change it on the 3620. The 1721 at the remote end let me change it without a complaint. Furthermore, I assumed that I'd lose the connection to the 3620's corresponding subinterface due to the mask mismatch until I changed it too, but it still runs. I want to change the mask on every subinterface of the 3620. Do I have to wipe out the entire config and build it from scratch with /30 addresses? Thanks for listening.