Flashing a Linksys WRT54G WirelessG Router

1
Flashing a Linksys WRT54G Wireless-G Router

• A brief introduction.

2
Tools of the Trade

• Firmware The Software Innards of the device.
  NOTE Linksys firmware for this unit is open
  source.
• TFTP - The utility that we use to place new
  versions of the Firmware in the unit.

3
TFTP

• TFTP (Trivial FTP) is part of the TCP/IP protocol
  suite and is specified in RFC1350
• It is very widely implemented and used for low
  level file transfers (primarily flashing images)
• Normally there is no authentication however the
  Linksys routers TFTP server DOES require a simple
  password authentication

4
Methods of Flashing.

• There are 3 methods of flashing the unit.
• Using the webpage based flashing utility that is
  in the existing firmware
• Using windows based firmware upgrade utility that
  comes from Linksys
• Using a modified TFTP client on a Linux system
  to push an image directly after powering the
  unit.
• All 3 methods Perform the same operation. The
  difference is how much user intervention is
  required.

5
The Setup

• In my test setup I used a laptop running Linux as
  my local machine. The router was not connected to
  any WAN.

6
The Process

• The Units Default IP address is 192.168.1.1
• Preopen the TFTP client (with password) and set
  the put command (note file should be named
  code.bin), but do not press enter. The client
  will not attempt to connect until you tell it to
  place the file
• Power on the Unit
• Immediately press enter

7
The Result
8
Failed attempts

• If the flashing fails because you waited to long
  to initiate a connection nothing will happen,
  youre request will be ignored.
• If it fails during the flashing process, the unit
  will no longer be able to boot, and will have to
  be re-flashed.
• There is a recovery mode that can be accessed by
  holding the reset switch down for 30 seconds.