I recently had to dust off an old Cisco switch to setup a lab here in my home office. I had no clue what the enable password was so I needed to hard reset the box to get in. Being all in on cloud, I have forgotten more hardware knowledge than I’d care to admit to. I no longer have any Windows based machines in the house with serial ports, so here’s a what I gathered to reset the switch using my Macbook Pro:
- USB to RJ-45 Serial Cable (here or search eBay for “Cisco USB RJ45 FTDI”.
- USB Serial driver for OSX (Virtual Com Port driver)
- The relevant Cisco password recovery page.
After installing the FTDI USB serial driver, I read the man page on “cu” to get the options right. The last time I used something similar was “tip” on my NeXTstation (yeah I’m old and still have it). So anyway, after finding the correct tty device, here we go:
# cu -l /dev/tty.usbserial-A501VIU9 -s 9600 --parity=none --nostop Connected. ROMMON: Cold Reset frame @0x00000000 ROMMON: Reading reset reason register ROMMON: Valid NVRAM config System Bootstrap, Version 12.0(7)W5(15a) RELEASE SOFTWARE Copyright (c) 2000 by cisco Systems, Inc. ROMMON: Initializing exceptions ROMMON: Initializing TLB ROMMON: Initializing cache ROMMON: Sizing and zeroing main memory ... 64 MBytes ROMMON: Sizing non-volatile memory ... 128 KBytes cat2948g platform with 65536 Kbytes of main memory [ ... ]
You may need to reset/power cycle the switch to see activity on the tty device.
The password recovery instructions say to send a “break” to the switch upon power cycle (within the first 60 secs). To do this with “cu”, you’ll need to use the cu escape command to send a break. This is ~# by default. Once sent, you should see something like:
monitor: command "boot" aborted due to user interrupt rommon 1 > rommon 1 >
You should be golden with the directions at the point.