802.11b WiFi Channels

In the United States and Canada there are 11 channels available for use in the 802.11b 2.4GHz WiFi Frequency range. This standard is defined by the IEEE.

Channel Lower Frequency Center Frequency Upper Frequency
1 2.401 2.412 2.423
2 2.404 2.417 2.428
3 2.411 2.422 2.433
4 2.416 2.427 2.438
5 2.421 2.432 2.443
6 2.426 2.437 2.448
7 2.431 2.442 2.453
8 2.436 2.447 2.458
9 2.441 2.452 2.463
10 2.451 2.457 2.468
11 2.451 2.462 2.473

There are only  3 non-overlapping channels available in the 802.11b standard.These are Channels 1,6, and 11. For WiFi access points that are located near each other it is recommended that they each use one of the above non-overlapping channels to minimize the effects of interference.

This overlapping of 2.4GHz channels are better visualized from the chart below.

80211-frequency-channel-map.jpg

Source: http://www.moonblinkwifi.com/2point4freq.cfm

Recovering From A Failed Firmware Flash on WRT54GL Using DD-WRT .v24

Flashing a WRT54GL v1.1 directly from stock (Linksys) firmware to Standard v24-sp2 will result in a failure. But, you might be able to ping the interface on the router (192.168.1.1). If so, the following will help ‘un-brick’ a failed firmware flash…

Download the following two items:

http://www.i-lan.com.au/downloads/tools/Router_Tools/V4.1.0/Router_Tools_V4.1.0.zip

http://downloads.linksysbycisco.com/downloads/FW_WRT54GL_4.30.12.3_US_EN_code.zip
The first is a TFTP router tool, the second is the stock Linksys firmware. Install the Router Tool, unzip the Linksys firmware. Fire up the Router Tool, enter the router IP (192.168.1.1), browse to the Linksys firmware for the second field, leave the password (3rd field) blank.

Make sure that your PC is set to a 192.168.1.X  address. Use a static address, not a DHCP assigned just to be sure! Unplug the 54GL router. Hit send on the Router Tool and quickly plug the router in. It should give you a progress indication as it uploads the firmware. If you get an error message right off the bat, click Send again. You may lose your IP if its set via DHCP after the send is over. The second box that the tool pops you can click on “Skip” after a minute if it doesnt go away. Fire up the browser and get (hopefully) to the interface.

Flashing a WRT54GL with DD-WRT

The following TWO (2) firmware versions should be downloaded in advance onto the PC that will be used for this operation:

1) The mini version used for the 1st flash: http://www.dd-wrt.com/routerdb/de/download.php?file=1190 

2) The standard version used for the 2nd flash: http://www.dd-wrt.com/dd-wrtv2/downloads/others/eko/BrainSlayer-V24-preSP2/07-21-09-r12533/broadcom/dd-wrt.v24_std_generic.bin

   The procedure for flashing is pretty straight forward. Toss the included CD and the sticker covering the back ports away. The CD is worse than useless anyway. You will need a standard straight-through CAT5 cable, which is the “regular” variety network cable. Connect the cable from a PC to one of the four LAN ports of the 54GL. Make sure that you don’t have any other connections (wireless or wired) by either unplugging other NICS or disabling the wireless card if it has one.

   I don’t know how your PC is currently configured IP-wise, but most likely it’s getting a DHCP lease. So, open a command line (Start->Run),  type in ‘cmd’ & hit OK. A good ole DOS box should open, the type in “ipconfig /release” (no quotes) followed by “ipconfig /renew” (no quotes). You should get an IP in the 192.168.1.0/24 subnet (probably 192.168.1.100). Alternatively, you can set a static IP using something within the 192.168.1.0/24 subnet, such as 192.168.1.2 (netmask 255.255.255.0 and gateway 192.168.1.1).

   Back to the Start->Run and type in http://192.168.1.1 and hit OK. Should take you to the router login, which is a blank username and a password of “admin” (no quotes). Go to the Administration -> Firmware area. Having downloaded the DD-WRT .bin file(s) somewhere on this same machine, you will simply browse to it from within the firmware GUI and click apply or update. For the first time, use the mini version! You will re-flash afterwards to the standard. If you try to flash the standard version first, you will brick the router!

   Now, this is important! Once it starts doing the upgrade, walk away! If you smoke like I do, go have a cigarette. Give it about 5 minutes. Wait for the device to re-flash itself and report complete. Don’t touch that Continue button. Just wait 5 full minutes.

   Then unplug power from the router. Hold the reset button in with a pen or pencil while plugging power back in. Continue holding the reset button for 30 seconds. Let the router boot up once more (the power LED will stop flickering when it’s booted).

   Now, fire up your browser and go to http://192.168.1.1 again.  The newest build asks for a username and password reset before continuing. The older builds just brought up a login box which use a generic username & password combo of “root” and “admin” respectively. Get back into the administrative tab of the new interface and re-flash the firmware using the Standard version this time. Use the same procedure (smoke a cigarette while flashing, unplug & reset, etc.). Afterwards, you should be good to go!