Using a Hardware DHCP Server to Share an Internet Account

One of the best ways to share an Internet account is to use a hub device that provides DHCP services to the network. These devices have the DHCP software built in and handle the administration of IP addresses for the network automatically.

In addition to basic DHCP services, some of these devices also include special features, such as built-in firewall protection for your network.

The general steps for installing and using such a device are the following:

  1. Choose and obtain the device.

  2. Install the device on your network.

  3. Configure the device to connect to the Internet.

  4. Attach the computers and other devices to the network and configure each device to use the DHCP server.


Not all ISPs support sharing a single Internet connection. Make sure that you check the agreement you have with your provider to make sure that sharing an account is within your rights under that account. Some configurations can actually block access to your account by a hub or other sharing device, thus preventing you from sharing the account using a hardware device. Before you purchase a hub, make sure that it is compatible with your Internet account or else you might end up wasting your money.

Choosing and Installing a DHCP Hub

Choosing a DHCP hub is very similar to choosing an Ethernet hub. For example, these hubs offer different numbers of ports, different speeds, and so on. In addition to the DHCP services that they provide, the major difference between standard Ethernet hubs and DHCP hubs is that DHCP hubs also offer a variety of other special features.

For help choosing and installing an Ethernet hub, see "Finding and Installing an Ethernet Hub," p. 710.

For help installing and configuring a network, see Chapter 25, "Building and Using a Network," p. 721.

For help with protecting your Mac from Net attacks, see "Defending Your Mac from Net Attacks," p. 803.


The AirPort Hardware Access Point is a DHCP hub; its most special feature is that it can communicate with other devices wirelessly.

One of the most important of these special features is a firewall. Installing a DHCP hub that includes a firewall protects the devices on your network from being attacked by hackers coming to your network from the Internet.

One form of firewall is the Network Address Translation (NAT) standard. Using NAT, there is one IP address for your network. The device providing NAT services shields the devices on your network by using a set of internal IP addresses for those devices. Thus, hackers trying to attack the only IP address that they can see get the hub device, which is typically immune to such attacks. Thus, your network is protected from external attack.

Various such devices are available, such as the Asante DLS/Cable Router (see Figure 26.3).

Figure 26.3. This Asante hub enables you to share an Internet account with multiple computers.


Some of my favorite sharing and networking hubs are produced by Linksys (see Figure 26.4). Linksys hubs provide excellent features and are easy to install and configure. These hubs enable you to share an Internet account and provide NAT protection for your network.

Figure 26.4. Linksys produces excellent sharing hubs that are easy to install and configure.



You can learn more about the Linksys products by visiting

Clumps of Data

When data is communicated across a network, it is done so in "clumps" of data. These "clumps" of data are more properly called packets. Each packet contains information that identifies its origin and destination (this is used to assemble all of the packets together into a useful string of data). When a firewall filters IP packets, it examines each packet that comes into the network to make sure that it originates from the expected place. It rejects any packets that do not meet its requirements, thus protecting the network from unexpected traffic, which is likely to have been generated by hacking activity. Packet filtering adds an additional layer of protection for a network.

The XRouter Pro is another example of a sharing hub that is simple to install and configure. For most homes or home offices, the XRouter is an excellent choice.



You can learn more about the XRouter Pro by visiting

Because of space limitations, I will be focusing on XRouter Pro in the remainder of this section. However, other devices, such as the Linksys hubs, can be installed and configured in a fashion similar to the XRouter Pro.

Installing a DHCP Server

Installing a DHCP hub is similar to installing a standard Ethernet hub.

  1. Connect the output from the cable or DSL modem to the WAN port on the hub.

  2. Connect the Ethernet cable from each computer to a port on the XRouter.

  3. Connect the XRouter's power supply.


You can attach the XRouter Pro to an existing Ethernet hub to provide its services to more than four devices at a time. To do so, connect one port on your current hub to the crossover port on the XRouter and use the crossover switch to select the crossover mode.

In the same way, you can also chain multiple hubs together to share an Internet account among more than four devices. For example, you can connect an AirPort Base Station to the hub to add AirPort-equipped devices to the network.

Configuring Mac OS X Macs for DHCP Services

After the physical connections are made, you need to configure each computer on the network to use DHCP for TCP/IP services.


Consider creating a location for each TCP/IP configuration you use. This makes switching between configurations simple and fast.

To learn how to configure and use the Location Manager, see "Configuring and Using Locations," p. 872.

To configure machines on a network to connect to a DHCP server, follow these steps:

  1. Open the Network pane of the System Preferences utility.

  2. Choose the location you want to configure from the Location pop-up menu.

  3. Choose Built-in Ethernet from the Show pop-up menu (assuming that you are connecting to the hub through Ethernet, of course).

  4. Click the TCP/IP tab.

  5. Choose Using DHCP from the Configure pop-up menu (see Figure 26.5).

    Figure 26.5. Typically, configuring a Mac to use a DHCP server is simply a matter of selecting Using DHCP from the Configure pop-up menu.



    Some DHCP servers will require that you use a DHCP Client ID name. If so, enter that name in the DHCP Client ID field.

  6. Click Apply Now to save the configuration.

  7. Close the System Preferences utility.

  8. Repeat these steps or use similar steps to configure the Macs on your network. For example, for Macs running Mac OS 9, use the TCP/IP control panel to choose Using DHCP Server.

  9. Configure the other devices on your network so that they use DHCP.

Configuring a DHCP Hub

After the hub is physically connected to your network and the other devices are installed and configured, you need to configure the hub. How this is accomplished varies among different devices, but most devices enable you to use a standard Web browser to configure the hub.

To install a typical DHCP hub, do the following:

  1. Launch a Web browser.

  2. Move to the IP address for the hub (the XRouter's IP address is

  3. When prompted, enter the username and password, and then click OK (the XRouter's username is blank and the password is admin). You will see the administration screen for the device (see Figure 26.6).

    Figure 26.6. This Web page is being served by the XRouter Pro and enables you to configure the hub.


  4. Configure the hub following the instructions provided by your ISP. You configure the hub using the same settings as you would for a computer with which you were accessing the Internet account. For example, if your ISP provides manual IP addresses, use the Static or Manual option to configure the hub.

    For help configuring an Internet account, see Chapter 10, "Connecting Your Mac to the Internet," p. 233.

  5. Quit the Web browser.


Make sure that you explore the configuration options your hub provides. For example, some hubs will enable you to assign fixed IP addresses to certain devices. These addresses are provided in a range of addresses that your hub provides (the first three sets of numbers in the IP address are the same for all the devices on the network, but you can choose the fourth set from a specific range of numbers). One use for this is to enable file sharing across those devices. Because you use IP addresses to share files under Mac OS X, having a fixed IP address enables you to connect to the same machine each time. If you allow the server to assign addresses, the address for each machine can change as machines connect to and disconnect from the network.

The machines on your network should be able to access the Internet using a single account. If your hub provides NAT services, your network is relatively secure from outside attack because the internal IP addresses of devices are not exposed to the Internet.


If your hub provides a firewall, explore its configuration page to control how your network access is configured. Typically, you can limit the access to specific URLs or direct all traffic to a specific machine on your network.


If none of the machines on your network is able to access the Internet, see "None of the Computers Can Access the Internet" in the Troubleshooting section at the end of this chapter.

    Part I: Mac OS X: Exploring the Core
    Part III: Mac OS X: Living the Digital Lifestyle