Wednesday, July 2, 2014

How to enable or disable DHCP on a Linksys WRT54G Wireless Router

Like many wireless routers, the Linksys WRT54G serves double-duty as a DHCP (Dynamic Host Configuration Protocol) server.  The router controls which IP addresses are available for use on your local network, and it sets up and manages leases for those addresses.

To turn DHCP on or off for your WRT54G, log in to your router's web interface by typing the router's IP address (typically into your web browser and then entering your username and password.  Once you've logged in, you should be looking at the Basic Setup page, under the Setup tab.

Most of your DHCP options are located on the bottom of that page.  By choosing Enable or Disable next to DHCP Server, you can turn the DHCP functions on or off.  (If you disable DHCP, you'll need to set up IP addresses for the each of the devices on your network manually.)  Below that, you can select the range of IP addresses to make available by designating a starting IP address and then choosing the maximum number of users you want to allow.

Whenever a computer requests an IP address from a DHCP server, the address is "leased" for a specific period of time.  Next to Client Lease Time, you can decide how long to make your leases, in minutes.  Leases are automatically extended as necessary, so the only thing this will really affect is network traffic if you have a lot of devices and short lease times.  By setting the lease time for zero, leases will be granted for 24 hours.

Any device that currently holds a DHCP lease is kept track of in the DHCP Clients Table.  To view this table and see what devices are on your network, go to the Status tab (last one on the right) and select the Local Network sub-heading.  Then click the gray button labeled DHCP Clients Table.  (This table can be a good network security tool, to make sure no unauthorized computers or other devices are accessing your network.)

When you click the button, a new window will open up with a list of devices that currently have active IP addresses through your DHCP server.  (Your router won't be on this list because it keeps a static IP address for itself.)  Any connected device with an IP address will be displayed, including smart phones, switches, and other network devices.  You may even find your video game system or television set-top box here.

You can view each device's name, IP address, MAC address, and lease expiration time.  The entries are listed in order of IP address, and by checking the lease times, you can see how long each device has been connected.  (Though if the lease has been renewed, you won't be able to see that information.)  Click the Refresh button at the top right to refresh the list if you've had it open for a while.

If you do find a device on this list that shouldn't be accessing your network, you can take away its IP address by putting a check in the box next to its lease expiration time and clicking Delete.  While monitoring this list is a good security policy, you should also be taking other measures to secure your network, such as disabling SSID broadcasting, enabling MAC address filtering, and using WEP, WPA, or WPA2.

(Originally published on, October 2010)

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