I have a pair of 2522's with serial modems connected to the ports, and remote sites that dial in. They are to be replaced by 2821's but I am seeing some strange behaviour.
When I plug the modems into the 2821s, the ports come up as (looped), and constantly see interface resets. This can be resolved by applying "no physical-layer async" to the port, which clears the configuration, and then upon repasting the configuration in, the port works. The other end can dial in fine. Without performing no phys async, the receiving modem hangs up near-instantly, or directly after hand-shaking.
Does anyone have any idea what may be causing this?