We have Cisco 1811 and Cisco 2801 routers at each of our branch locations, Lets say its IOS gets corrupt. We have Aux ports and telephone lines plugged in for every router. Would I be able to use the Aux port and dial into it?(It would be in ROMMON Mode?) We have USB flash sticks also in every router. We wont have any IP connectivity from remote branch to the Head Office . The remote site engineer can only be of any "Physical help"
What would be the best procedure to restore the corrupted IOS image.
You might consider connecting a modem to the console port. Here is a reference with advantages/disadvantages and configuration:
For quick restoration, I would keep a flash (or USB) with a backup image or have a second image on the flash if you have enough space. It is possible to boot them from rommon like: boot flash:.
If it is not possible, we would have xmodem (very slow) or download via TFTP but both would be difficult if the onsite engineer has no knowledge of the procedure at all: