Building Wireless Community Networks, Second Edition

Chapter 4. Using Access Points

As we discussed in Chapter 3, an access point (AP) is a piece of hardware that connects your wireless clients to a wired network (and usually on to the Internet from there). As with any piece of bridging hardware, it has at least two network connections and shuffles traffic between them. The wireless interface is typically an on-board radio or an embedded PCMCIA wireless card. The second network interface can be Ethernet, a dialup modem, or even another wireless adapter. Many access points now even include multiple Ethernet ports, which simplifies the creation of a trusted network segment.

The access point hardware controls access to and from both networks. On the wireless side, most vendors have implemented 802.11b access control methods (such as WEP encryption keys, “closed” networks, and MAC address filtering). Some have added proprietary extensions to provide additional security, such as more sophisticated encryption.^[9] Many access points also allow control over what the wired network can send to the wireless clients, through simple firewall rules. Much of this functionality is accessible through either a Java-based tool or a simple web page interface.

In addition to providing access control, the access point also maintains its own network connections. This includes functions such as dialing the phone and connecting to an ISP on demand, or using DHCP on the Ethernet interface to get a network lease. Most access points can provide NAT and DHCP service ...