Please check out the following article....
If you are not having luck with the serial cable, you could also try the management rj-45 port ( it's the one that is alone, single port ). Try some different serial cables to see if the serial cable is the problem. It should connect with 115200 8-N-1. Try to connect with a normal Ethernet cable, and set your wired nic to 192.168.10.2 255.255.255.0. The management ip by default is 192.168.10.1. ssh to 192.168.10.1, and then you can log in as admin, and use the cli to reset the controller:
WARNING: Resetting will clear all configuration except for the management port configuration. It will disconnect any clients currently using the system. Following the reset, the system will be rebooted.
Do you wish to continue? (y/n) n
Reset cancelled by user request.
EWC.enterasys.com# reset ?
Usage: reset [license] [mgmt]
If you have forgotten the admin password, then you will need to access via the serial port, and enter rescue mode to reset the password.
Based on the exchange above we have added the following to the GTAC Knowledge Site for future reference:
Another trick to get management ip if you do not know it, is to plug a cable into the management port. Then you can run wireshark on your machine, and see if you can see the ip address in any packets from the controller. You could to the same trick on the data ports. If enable management through data ports was selected, then you should be able to plug directly into one of those as well, and then ssh to that ip.
You can see the mgmt. port and serial port locations in the C25 Quick Install Guide located here: