Dual-Mode Access Points and Gateways

Wireless Residential Gateways

Even though sharing a broadband Internet connection is the top use driving Wi-Fi networks in the home, there is nothing inherent in a wireless access point to support the Internet. As I explained in Chapter 2, an access point is just a wireless Ethernet hub, and can be used to create a network without any Internet connection at all.

Internet connection sharing requires a router and a Network Address Translation (NAT) server. A Dynamic Host Configuration Protocol (DHCP) server is also very useful in a network based on the Internet protocol suite. Taken together, these items comprise a gateway, that is, an interface between two networks: your network and the global Internet.

It's easy enough to bundle a router with a NAT server and DHCP server into a single package with a wireless access point. To make local area networks easier to create, most vendors also add an Ethernet switch (see Chapter 2) to the mix as well. Router, NAT, DHCP, switch, and access point together become an 'all-in-one' wireless network appliance focused on providing an Internet gateway to a local area network. I call such an appliance a wireless residential gateway.

Not everyone uses the term, but there is a crying need for a new descriptive word or phrase to replace awkward concretions like 'Wireless access point + cable/DSL router and switch.' (That awful mess is what Linksys calls their very excellent BEFW11S4 appliance.) Residential gateways are quite common and very effective for small office/home office (SOHO) local area networks, and both save money and reduce cable clutter considerably.

Perhaps the best-known example of a residential gateway (the 'wireless' is often assumed) is the LinkSys BEFW11S4, shown in Figure 6.4. This unit is consistently shown as the best-selling Wi-Fi appliance in any stack rank of sales I see on the Web. In small networks needing only a single access point, this is the only piece of networking gear you'll need, apart from network client cards (either wired or wireless) installed in all computers or other devices connected to the network. Wireless client adapters connect to the built-in wireless access point. Wired Ethernet client adapters connect to one of the several Ethernet switch ports on the back of the unit.

Figure 6.4: The Linksys BEFW11S4: Wireless Residential Gateway. (Photo courtesy of Linksys.)

How these connections are made is fairly simple, as shown in Figure 6.5. A Category 5 patch cable connects your cable or DSL modem to the wide-area network (WAN) port on the residential gateway, and any computers requiring wired access are similarly connected to one of the four switched ports on the gateway. Machines with Wi-Fi client cards installed communicate with the gateway via its wireless access point.

Figure 6.5: A Wireless Residential Gateway.

Many residential gateways have an expansion port, which allows the connection of a 'slave' switch to provide additional wired ports. The Linksys BEFW11S4 has such a port, which it calls the 'uplink' port. The uplink port is attached to port 4, and when the uplink port is connected to a slave switch, port 4 is unavailable.

The router manages access to the 'wide area' network world beyond your LAN (usually the Internet), and uses its NAT server to share the WAN connection among the computers on your LAN. (I explained NAT operation in Chapter 3.) The switch directs those packets to the correct machines, and the access point provides wireless connection to machines not connected to the gateway by CAT 5 cables.

Note that the wireless access point is switched just as the hardwired computers are. All computers connected wirelessly to the access point share one switched connection, and thus share the data throughput of that one switched connection.

One caution about using residential gateways: They're not suitable for networks that must support roaming. In other words, if your house or office is so large as to require multiple wireless access points to cover it all, don't attempt to use multiple residential gateways. Roaming (being able to walk around with a Wi-Fi-equipped laptop or PDA and connect seamlessly through multiple APs) is a sticky issue in Wi-Fi right now. The standard does not specify in detail how roaming is to be handled, so different manufacturers handle it in different (and often incompatible) ways. If you need to implement roaming, always inquire of your Wi-Fi vendor to make sure a given access point supports it, and then use the same manufacturer and model for all APs in the network.

Another thing to keep in mind if you're thinking about experimenting with bridge mode or with access points in client mode: None of the wireless residential gateways I've tried (including the Linksys BEFW11S4) support either bridge mode or client mode. They're not designed for versatility, and they're really one-trick ponies. Still, for 85% of the people who implement a Wi-Fi network, that one trick is all they need the device to do.