Cisco 4900M ROMMON Recovery

Cisco 4900Ms are interesting platforms to work with. They are fantastic as layer 2 devices, but with MLS images, I’ve had some “challenges” in the past that resulted in the need for a ROMMON recovery. One of these issues was the switch deciding to format its flash after a reboot (wonderful!).

The ROMMON recovery procedure is a bit different to the norm (in that you use the management port) so it’s posted below. The TFTP server is as an example. All configuration is done via the console port on a remote terminal server.

rommon 1 >set interface fa1
rommon 2 >set ip route default
rommon 3 >boot tftp://

The switch then boots up via tftp – this may take quite a while depending on bandwidth and latency. As a reference, booting off that image over a 70ms latency Gig link via tftp took 45 minutes so you will have to be patient unless you have someone local with a laptop that can run a server to load the image from. You’ll see the following (love the Star Wars references on this platform!):

Tftp Session details are ....

 Filename     : /cat4500e-entservicesk9-mz.122-54.SG1.bin
 IP Address   :
 Loading from TftpServer:

 Received data packet #  50659

 Loaded 25936915 bytes successfully.

Rommon reg: 0x00004380
Reset2Reg: 0x00001FFF
Tatooine controller 0x0B46AD69..0x0B4D21F5 original size:0x0012635C##
Forerunner controller 0x0B4D21F6..0x0B593DC6 original size:0x001CE7CF
diagsk5 version 4.1.6

You now have to get an image on to the switch seeing as the IOS image is only in memory, not on flash. You will also need to make a basic config to save. Use FTP at the very least to copy the image down or you will be waiting forever. As per a previous post, the config register must be changed on this platform or you will have headaches later!

Switch#conf t
Enter configuration commands, one per line.  End with CNTL/Z.
Switch(config)#ip vrf mgmtVrf
Switch(config-vrf)#vtp domain null
Switch(config)#vtp mode transparent
Setting device to VTP Transparent mode for VLANS.
Switch(config)#interface FastEthernet1
Switch(config-if)# ip vrf forwarding mgmtVrf
Switch(config-if)# ip address
Switch(config-if)# speed auto
Switch(config-if)# duplex auto
Switch(config-if)#ip route vrf mgmtVrf
Switch(config)#ip ftp source Fa1
Switch#copy ftp://user:password@ bootflash
Destination filename [cat4500e-entservicesk9-mz.122-54.SG1.bin]?
[OK - 25936915/4096 bytes]

25936915 bytes copied in 528.374 secs (49088 bytes/sec)
Directory of bootflash:/

   19  -rw-    25936915  May 13 2013 09:42:20 +00:00  cat4500e-entservicesk9-mz.122-54.SG1.bin

122007552 bytes total (88629248 bytes free)

Switch(config)#boot system flash bootflash:cat4500e-entservicesk9-mz.122-54.SG1.bin 
Switch(config)#config-register 0x2102
Switch(config)#wr mem
Building configuration...
Compressed configuration from 2735 bytes to 1154 bytes[OK]
Switch#sho bootvar
BOOT variable = bootflash:cat4500e-entservicesk9-mz.122-54.SG1.bin,1;
CONFIG_FILE variable does not exist
BOOTLDR variable does not exist
Configuration register is 0x102 (will be 0x2102 at next reload)
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2 Responses to Cisco 4900M ROMMON Recovery

  1. Juan Houghton says:

    Great post. Help me a lot. Thank you.

  2. Luana Zanetti says:

    Thank you! It helped a lot!

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