Building Wireless Community Networks, Second Edition

Vital Services

A network can be as simple as a PPP dialup to an ISP, or as grandiose and baroque as a multinational corporate MegaNet. But every node on a multimillion dollar network in Silicon Valley needs to address the same fundamental questions that a dialup computer must answer: who am I, where am I going, and how do I get there from here? In order for wireless clients to easily access a network, the following basic services must be provided.

DHCP

The days of static IP addresses and user-specified network parameters are thankfully far behind us. Using DHCP (Dynamic Host Configuration Protocol),^[6] it is possible (and even trivial) to set up a server that responds to client requests for network information. Typically, a DHCP server provides all of the information that a client needs to begin routing packets on the network, including the client’s own IP address, the default Internet gateway, and the IP addresses of the local DNS servers. The client configuration is ridiculously easy and is, in fact, configured out of the box for DHCP in all modern operating systems.

While a thorough dissection of DHCP is beyond the scope of this book, a typical DHCP session goes something like this: a client boots up, knowing nothing about the network it is attached to except its own hardware MAC address. It broadcasts a packet saying effectively, “I am here, and this is my MAC address. What is my IP address?” A DHCP server on the same network segment is listening for these requests, and responds ...