Building Wireless Community Networks

Chapter 4. Using Access Points

As we discussed in Chapter 3, an access point 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 onboard radio or an embedded PCMCIA wireless card. The second network interface can be Ethernet, a dialup modem, or even another wireless adapter.

The access point hardware controls access to and from both networks. On the wireless side, most vendors have implemented 802.11b access control methods (like WEP encryption keys, “closed” network ESSIDs, and MAC address filtering). Some have added proprietary extensions to provide additional security, like public key encryption.^[6] Many access points also allow control over what the wired network can send to the wireless clients, through simple firewall rules.

In addition to providing access control, the access point also maintains its own network connections. This includes functions like 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 to the wireless clients, thereby supporting multiple wireless users while only requiring a single IP address from the wire. Some support direct bridging, allowing the wired and wireless networks to exchange data as if they were physically ...