Posted by arlene

Many small- to medium-sized networks use the router that provides Internet access as a DHCP server, using it to provide network addresses to client PCs. Configuring a router to act as a DHCP server is not difficult (most routers are configured to provide IP addresses by default), but you should be familiar with the process so you can make changes to the configuration, and, most important in the case of a wireless access point (WAP) or wireless router, limit the number of IP addresses provided. By limiting the number of IP addresses to the number of clients on your network, you can help minimize the possibilities of unauthorized users borrowing your network for Internet access or hacking.

To view or change the configuration of your router’s DHCP settings, follow this basic procedure. This procedure is based on that used by Linksys routers, but others are generally similar:

1. Log into the router’s built-in configuration web server. Enter the router’s IP address (this is the IP address listed as “default gateway” by the ipconf ig command or equivalent and enter the username and password needed.
2. After logging into the router, open the DHCP configuration screen.
3. If no devices are able to get an IP address, make sure the DHCP server is enabled. The DHCP server function should be disabled only if all clients have manually assigned IP addresses or if another device on the network is being used as a DHCP server.
4. Specify the starting IP address. Make sure the starting address is not already in use by a device with a manually assigned IP address.
5. Specify the number of DHCP clients. If you enter 10, the router provides addresses to up to 10 clients. You should adjust this number to reflect the maximum number of clients that might connect to this router. For example, if you have a mixed wired and wireless network with three wired clients and up to two wireless clients, make sure you specify 5 for the number. If you specify a number less than 5, one or more of the wireless clients will not receive an IP address when they connect. If you specify a number greater than 5 and don’t secure your wireless network, however, unauthorized clients might receive a DHCP address from your server and borrow your bandwidth or attempt to hack your network.
6. To determine what clients are currently using an IP address provided by this router, click the DHCP Clients button. On some routers, this information might be displayed on the same screen as the remainder of the DHCP information. Note that the computer (client) name and MAC (adapter physical) address are listed for each client.
7. To refresh the listing.
8. If an unauthorized computer is listed when you display DHCP clients, click the box next to the computer’s MAC address and click Delete. This clears the connection from that computer to the router.
9. Close the dialog. Click Apply or OK to accept changes to the router configuration, or click Cancel to discard changes to the configuration. The router restarts and your changes to the router configuration are now operational.

Note that you need to have a list of authorized computer (client) names to determine which computers or devices are authorized when you view the list of active clients. You can generate this information by running the host name command on each client PC.

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