Can't change subinterface IP address

[4DeanB]

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.

 

[bell1996]

4DeanB -

You're going to have to remove the 192.168.20.0 /24 subnet from the router. Then you can re-address the subinterfaces with 192.168.20.x /30. The router is smart enough to know that the 192.168.20.0 /24 subnet exists in the router. Therefore denying you the ability to re-address with 192.168.20.x /30.

You may want to investigate using "IP Unnumbered