**DISCLAIMER** The following instructions are provided without warranty of any kind. Flashing firmware does not come without risk. I will not be held responsible for any resulting equipment failure or otherwise undesirable results. Proceed at your own risk.
This tutorial explains how I successfully flashed my Linksys WRT54GL version 1.1 with the open source dd-wrt version 23 SP2 VPN firmware (generic). If you happen to have Linksys WRT54GL version 1 rather than 1.1 (you can tell by the serial number prefix of CL7A for version 1.0 and CL7B for version 1.1 per the Wikipedia entry and dd-wrt Wiki), you may have to follow slightly different instructions. The main difference is that you will need to flash to a smaller version of the dd-wrt firmware (the mini version) first due to a flash file size limit on the version 1.0 WRT54GL firmware before flashing to the standard, VOIP, or VPN versions.
As a bit of background information, I’m used a fully patched (as of April 6, 2007) Windows XP Pro with Service Pack 2 (SP2) and Internet Explorer 6 during the firmware upgrade process. The OS and web browser shouldn’t matter that much, but I have heard reports of Firefox causing some problems with the Flash for some people in the past though others have claimed to use Firefox without any problems–just a word of caution.
Before you begin, download the package and version of the dd-wrt firmware best suited to your needs though this tutorial walks through flashing to the open source dd-wrt version 23 SP2 VPN firmware. Once you’ve downloaded the file, go ahead an unzip the files. The zip package contains several files, you will only need the “dd-wrt.v23_vpn_generic” file. We’re going to be using the generic file rather than the wrt54g file because we’re going to be using the web GUI to upload the file. Continue reading