This occurs when the router is reloaded, and is caused by echoing being enabled on the modem.
If a Cisco 2600 or 3600 series router goes into ROM Monitor (ROMmon) mode after a reload when a modem is connected to the console port, perform the following steps:
- If possible, disconnect the modem from the console port and reload the router to be sure the modem is causing the router to go into ROMmon mode.
- If the router boots normally without the modem connected, disable echoing on the modem. Contact the modem manufacturer for procedures on disabling echo.
- After the echo feature is disabled, reconnect the modem to the router's console port, and reload the router in order to test the workaround.