In this chapter we explored the various networking features available in PHP and also the technologies underlying these features to some extent. While most of the inner workings of the TCP/IP protocol are not exposed to the application programmer, we still need to understand certain aspects of the protocol suite. Naming of resources in an IP network is one of them. DNS is the de facto "name-to-IP address" resolution mechanism available and PHP supports quite a few functions to access DNS resources. YP/NIS is another such mechanism though mostly constrained to an intranet environment. PHP has YP/NIS functions to do resource lookups.
Socket support in PHP as of release 4.0.6 is still nascent, but we nevertheless look at the available interface for using sockets to enable communication between client-server applications. During the course of the chapter we also developed a mail client application to tie together our understanding of the socket and DNS API. The SNMP protocol addresses management of network resources, and PHP provides some rudimentary support for SNMP agent operations.