1. Install/prepare a tftp server like 3CDaemon and make sure that it is reachable from router
2. First of all before upgrading any working image take a backup
3. For taking a backup use following commands
2600#copy flash tftp
give the tftp server ip address, destination file name
4. For uploading run following commands
2600#copy tftp flash
give source and destination file names and tftp server ip address
In case you don't have a working image and unable to boot router
1. Reboot Router and press cntrl+break . Now you will be in rommon mode.
2. Now give IP_ADDRESS, IP_ADDRESS_NETMASK, DEFAULT_GATEWAY,TFTP_SERVER,TFTP_FILE
3. finally give commands tftpdnld
4. Now rommon > confreg 0x2102
5 rommon >reset
6 set boot image from
2600(config)#no boot system
2600(config)#boot system flash
Now you have done !!
