January 23, 2012

Use DHCP Reservation to Minimize Unauthorized Connections to your DLink DIR-300 Wireless Router

If you're living in a condo or an apartment building, it's so easy for your neighbors to make use of your wireless Internet connection especially if you did not configure any security settings in your wireless router. If you're experiencing slow Internet speed when you're surfing, then it could be that a few of your neighbors may be availing themselves of free Internet connection from your wireless router.

There are various ways of minimizing unauthorized access to your wireless router like for example setting up access control and using strong encryption in your security settings. But there is  yet another way by which you can control the number of computers that may access your wireless home network and this is through Dynamic Host Configuration Protocol (DHCP) reservation. I am using the DLink DIR-300 wireless router as an example but this scheme can also be implemented in other brands of wireless routers.

The scheme works by using a customized Internet Protocol (IP) addressing plan that includes few enough addresses but is able to accommodate all the computers that you expect to be connecting with your network. What you will do is to give your DLink DIR-300 DHCP server only one IP address to assign to anyone wishing to connect with your network. You will then assign the first few addresses statically to existing computers in your house and put these in the DHCP Reservation list of your DLink DIR-300 wireless router. If anyone you know wishes to use your Internet connection, then you just use the next available address and enter it together with the machine address of the wireless adapter of her computer in your router's DHCP Reservation list.

Say you have decided to use the IP address range 10.20.30.48 to 10.20.30.63 with a subnet mask of 255.255.255.240 giving you 14 usable addresses for computers in your network. You can then give the highest valid IP address (10.20.30.62) to your DHCP server for giving to anyone that wishes to connect with your network. Then you can assign the first few lower addresses to actual computers in your network and then enter them in the DHCP Reservation list of your DLink DIR-300 wireless router. You cannot use 10.20.30.48 and 10.20.30.63 because they are your network address and broadcast address respectively.

Gather first all the machine addresses of the wireless adapters of all computers in your house. Assign the first available address (10.20.30.49) to your wireless router and the next few addresses to the rest of computers in your network. If you have four computers that will actually use the network, then you would be using up the first five IP addresses in your IP address range.

Open and logon to your DLink DIR-300 web based configuration program. Click on Maintenance at the top portion of the window and then click on Save and Restore on the top left hand side. Click on the Save button and save the configuration file to your hard disk. Click on Setup at the top of the window and then on LAN Setup on the top left hand side of the configuration page. Type 10.20.30.49 on the blank opposite Router IP Address. Type 255.255.255.240 on the blank opposite Default Subnet Mask. Put a check mark on Enable DHCP Server. Type 62 on both of the two boxes opposite DHCP IP Address Range.

Go down to the DHCP Reservation and fill out four random computer names on the Computer Name column, for example computer1, computer2 and so forth. Type the next four IP addresses after the router's address on the blanks under the IP Address column. On the first four blanks under the MAC Address column, enter the machine addresses of the actual computers that are to connect to the network. In Windows computers, you can find the machine address of the computer's wireless adapter by typing ipconfig /all in a command prompt window on your desktop. Put a check mark on the left hand side of the four rows of data that you have entered. Click on the Save Settings button at the bottom of the page.

Restart all computers in your network and check that they are receiving the static IP address reserved for them. Use the ipconfig /all command in a command prompt on Windows computers to find out what IP address and subnet mask had been assigned by your router's DHCP server. If something went wrong and your laptop did not receive the correct IP address, temporarily assign it with the correct IP address using your Windows control panel and restart it so you can access your router again to make the needed corrections. You will have to use the new router's address (http://10.20.30.49) to access the configuration page of your router again. If by any chance you got confused and want to go back to the original setting, you can re-upload the original settings that you have saved in your hard disk. But you have to manually assign a temporary valid IP address, subnet mask, and gateway address (your router's IP address) to your laptop if you want to do this.

If you were able to successfully changed your settings, only one other external computer that is setup to obtain IP address automatically will be able to connect to your network. To connect a friend's laptop to your network, get the machine address of its wireless adapter and enter it together with the next available IP address on the next blank row on the DLink DIR-300 DHCP Reservation list. Put a check mark on the left side of the row and click on the Save Settings button. Now you have more control on which computers to allow access to your network. However, external computers can still connect to your network if they are manually assigned one of the unused IP addresses in your IP address range. Hopefully, not everyone knows how to do this and thus the threat of too many unauthorized external connections is at least minimized.

Read my other article on a simple IP addressing scheme for using DHCP on your wireless home network at: http://publishtoweb.blogspot.com/2011/12/simple-ip-addressing-scheme-for-using.html.

Read my other article on how to setup DHCP in your DLink DIR-300 wireless router at: http://publishtoweb.blogspot.com/2012/01/how-to-setup-dhcp-in-your-dlink-dir-300.html.

Read my other article on how to maintain connectivity with your wireless router when changing its IP address at: http://publishtoweb.blogspot.com/2012/01/how-to-maintain-connectivity-with-your.html.