Undo the 2 screws on the back on the router as shown:
Opening the case of a Cisco 877 Router
Then undo the 3 screws securing the protective metal case beneath:
Accessing the flash and RAM slots in a Cisco 877 router
Swap the flash memory for the new larger bit:
Swapping the flash memory
Replace the case, plug in the power, connect the router to your computer using a console cable, and then power it on.
Fire up hyperterm or some similar program and connect to the router. It may complain about an inconsistent sector list in flashfs on boot up, and will also tell you that there is no bootable IOS image file in the flash memory. Once you are at the ROMMON prompt issue the following command:
format flash:
click ‘y’ and press enter to confirm the format operation
Once the format is complete, connect a LAN patch lead from you computer to the router. Assign an IP address to the LAN adapter of your computer such as 192.168.1.1/24. Fire up a bit of TFTP server software on your computer, such as Cisco TFTP server, or Solarwinds TFTP server
At the rommon prompt type the following, making sure you assign an IP address to the router that is in the same subnet as the IP that you assigned your computer, e.g.
IP_ADDRESS=192.168.1.254
then assign a subnet mask:
IP_SUBNET_MASK=255.255.255.0
then a default gateway:
DEFAULT_GATEWAY=192.168.1.254
then a TFTP server (i.e. the IP address you assigned your computer’s LAN adapter):
TFTP_SERVER=192.168.1.1
and finally the filename of the IOS image that you want to transfer back on to your router
TFTP_FILE=c870-advsecurityk9-mz.124-15.T12.bin
If you want to review the variables that you have set above any time just type:
set
Next issue the tftpdnld command to copy the IOS image to the flash memory of your router using tftp:
tftpdnld
Click ‘y’ to continue. This will take a few minutes. After that reboot the router and you’re done:
reset
oasysadmin 