Upload IOS via TFTP in ROMMON
It is recommended to maintain your network devices with updated IOS. However, it is highly recommended to plan & to prepare how to do a rollback in the worst case scenario, for example: if the router fails to boot properly due to corrupted image file or due to usage of new flash memory, etc.
To bypass this problem is just by let the router boot-up with the IOS from an TFTP itself.
First, make sure that the router is connected to a TFTP Server, also a valid ISO file is there.
During boot-up, press Ctrl+Break continuously so that the router goes into ROMMON mode.
Type the following command:
rommon 1 &amp;amp;gt; IP_ADDRESS=172.16.1.1 rommon 2 &amp;amp;gt; IP_SUBNET_MASK=255.255.255.0 rommon 3 &amp;amp;gt; DEFAULT_GATEWAY=172.16.1.100 rommon 4 &amp;amp;gt; TFTP_SERVER=172.16.1.100 rommon 5 &amp;amp;gt; TFTP_FILE=C3640-Ix-Mz_20122-15_20T2.bin rommon 6 &amp;amp;gt; tftpdnld -r IP_ADDRESS: 172.16.1.1 IP_SUBNET_MASK: 255.255.254.0 DEFAULT_GATEWAY: 172.16.1.100 TFTP_SERVER: 172.16.1.100 TFTP_FILE: C3640-Ix-Mz_20122-15_20T2.bin TFTP_VERBOSE: Progress TFTP_RETRY_COUNT: 18 TFTP_TIMEOUT: 7200 TFTP_CHECKSUM: Yes TFTP_MACADDR: XXX.XXX.XXX.XXX GE_PORT: Gigabit Ethernet 0 GE_SPEED_MODE: Auto . Receiving C3640-Ix-Mz_20122-15_20T2.bin from 172.16.1.100 ... ...
- Command 1: IP address of router interface
- Command 2: Subnet mask for the above IP
- Command 3: Default gateway for router (can be same as TFTP Server IP)
- Command 4: IP address of TFTP Server
- Command 5: Name of IOS to be used for bootup (including the .bin extension)
- Command 6: Direct the router to load the IOS on memory rather than downloading it to the flash
Please notice, booting a Cisco router from TFTP not used only for this situation, can also be used for other stuffs such as the router’s RAM inadequate, security solution, flexibility to use different IOS.