HOW TO: Share a Single IP Address Using a Router
 Follow these instructions to set up a router device that allows several computers to share a single IP address.

An Internet Service Provider (ISP) usually provides you with only a single IP address. Use this info if you have more than a single computer or device like a laptop and a desktop computer you want to use at the same time.  You can share your single IP address with all devices by using a router (or router and switch), a host with a shared Internet connection, or an all-in-one device that acts as a wireless access point, router, switch, and even a cable or DSL modem.

Before You Begin

To use this info you must have:

a wireless network interface card installed in each device
all documentation for your wireless cards
a router
a hub or switch (Depending on configuration)
two or three Category 5 or 5e Ethernet cables

Step 1a - Install and Configure Router (follow this step if you are NOT using a hub or a switch)

Follow these steps to install a router on your wireless network without using a hub or a switch.

Turn the power off for all devices connected to the network.
Obtain an Category 5 or 5e Ethernet cable that is long enough to connect your access point to your router.
Plug one end of the cable into any Ethernet port on the router, except the one marked WAN or UPLINK. (Some routers have only one other port, while others may have two, four, or even eight usable ports.)
Plug the other end of the cable into the Ethernet port marked LAN, located on the back of your access point.
Plug a second Category 5 or 5e Ethernet cable into the WAN port on the back of the router.
Plug the other end of the second Ethernet cable into the LAN port on the back of the Internet access device (cable or DSL modem).
Restore power to all devices, in this order: cable/DSL modem, router, access point, then all computers.
Turn on all computers attached to the network.
Make sure that any IP-sharing applications are disabled on all computers (WinProxy, Internet Connection Sharing, etc.).

Step 1b - Install and Configure Router (follow this step if you are using a hub or a switch)

Follow these steps to install a router and hub or a switch on your wireless network.

Turn the power off for all devices connected to the network.
Obtain an Category 5 or 5e Ethernet cable that is long enough to connect your access point to your hub or switch.
Plug one end of the cable into the Ethernet port marked LAN, located on the back of your access point.
Plug the other end of the cable into any Ethernet port on the hub or switch, except the one marked UPLINK.
Plug a second Category 5 or 5e Ethernet cable into the UPLINK port on the back of the router.
Plug the other end of the second Ethernet cable into any port on the router, except the one marked WAN. (Some routers have only one port, while others may have two, four, or even eight usable ports.)
Plug a third Category 5 or 5e Ethernet cable into the WAN port on the back of the router.
Plug the other end of the third Ethernet cable into the LAN port on the back of the Internet access device (cable or DSL modem).
Restore power to all devices, in this order: cable/DSL modem, router, hub or a switch, access point, then all computers.

Step 2 – Configure the Router

Access the router's interface.

• You may need to run a configuration utility provided by the manufacturer.
• You may need to use a web-based configuration utility from a computer attached to the network.
• If you have a wired Ethernet card, you may be able to use a special crossover cable.
• Often, you can access the interface by opening a Web browser and typing http://192.168.1.1 (the default setting for many routers designed for home use). However, your device may use a different method, such as a desktop software program.
• Many routers ship by default with a blank user name and standard password (for example, "admin"). Be sure to change this information the first time you log in.
• Configure the router settings according to its documentation. (Hubs or switches do not usually require configuration.) The following settings are basic functions common to most routers:

Router and Domain name. Contact your ISP to see if you need to enter a specific host name or domain name.

Enable DHCP for the WAN. Unless your ISP has provided you with a permanent (static) IP address, you should enable DHCP for the wide-area network (WAN) connection. This allows your router to obtain its public IP address from your ISP.

Enable DHCP for the LAN. The router can automatically assign IP addresses, subnet, and gateway information to all computers connected to your home network that are set to obtain information from a DHCP server. Alternatively, you can use permanent (static) IP addresses, but this requires in-depth knowledge of IP addressing.

Enable NAT. You can use network address translation (NAT) to re-address all data packets flowing out of your network. This function makes it look like all outgoing traffic is originating from one computer. Through mapping, incoming traffic is routed to the appropriate computer.

Block WAN. If it's available, this feature prevents outside computers from "pinging" your router and computers to see if they are active.

Filtering. Some routers can prevent certain computers or ports on the router from accessing the Internet. This feature usually requires you to assign static IP addresses to each computer on the network. Disabling 192.168.1.12 means the computer with that address cannot access the Internet. Disabling Port 2 means the second port on the back of the router cannot access the Internet.

Port Forwarding. Some routers can forward requests for certain services to specific services. This feature is normally used only if you are operating an e-mail or web server on your local area network. For instance, you may want to send all Web traffic to one computer configured with a static IP address. Note that this potentially opens your computers to outside attacks.

DMZ. Short for "de-militarized zone," this feature is normally used to temporarily expose a single computer for gaming, chatting, or remote access. It also makes that system more vulnerable to attack.

MAC Address Filtering. Finally, you can enter media access control (MAC) addresses, or unique identifiers for each hardware device. This gives you fine control over exactly which systems can access the network.

Step 3 -Test the Network Connection

Follow these steps to check your router setup.

Make sure the access point has power and that any wireless devices are within range of the access point.
Restart (or turn on) all devices connected to the network and check to see if you can connect to the network.

• If you are using this at the University, open your browser to load the Public Network authentication screen. Use your EID to log in. Then, you can access the Internet.
• All properly configured wireless devices should automatically connect when you use any application that accesses the network or Internet. If not, try the following solutions:
  - Check that device's TCP/IP settings - for example, is it using DHCP, or manually assigned IP addresses?
  - Completely power down the device and then turn it on.
  - For Windows systems using DHCP, click Start > Run and type ipconfig  /release. Then, click Start > Run and type ipconfig  /renew.
  - Check the access point as described in the access point install document.
  
• If you can see other computers on your network but cannot access the Internet, your LAN configuration is correct, but your WAN (Internet Service Provider) configuration is not. Open your router configuration utility or browser address.
  - You may need to power down your router and cable modem, wait several minutes, then restart them both. Many devices can cache data for a few minutes, even without power.
  - You may need to specify a different domain or DNS server in the WAN settings.
  - You may need to leave the domain name blank in the WAN settings.
  - You may need to request a new WAN IP address. Most router configuration utilities have a button for this task.
  Check your router documentation and call your ISP if you can't resolve the problem.
• If you can access the Internet, but can't see other computers on your network, your ISP and client TCP/IP configurations are correct, but your client LAN settings may be incorrect.
  - Completely power down the device and then turn it on.
  - Check your Network ID, workgroup, domain, or AppleTalk Zone to see if it matches those settings for other computers on the same network.

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