I've a 2610 Router with IOS 12.3(6a) [c2600-i-mz.123-6a.bin] connected to a 2520 Router with IOS 11.0(13) [igs-i-l.110-13]. I configured the routers to backup the connection w/ a telephone line but as son as the chat-script connects, the 2610 router closes the connection.
I've tested the same scenario but used a 2510 instead of the 2610. The connection was established w/o problem.
I've been searching information about IOS's incompatibility but haven't found anything.
Thanks in advance.