HTTP: The Definitive Guide

Step 1: Accepting Client Connections

If a client already has a persistent connection open to the server, it can use that connection to send its request. Otherwise, the client needs to open a new connection to the server (refer back to Chapter 4 to review HTTP connection-management technology).

Handling New Connections

When a client requests a TCP connection to the web server, the web server establishes the connection and determines which client is on the other side of the connection, extracting the IP address from the TCP connection.^[1] Once a new connection is established and accepted, the server adds the new connection to its list of existing web server connections and prepares to watch for data on the connection.

The web server is free to reject and immediately close any connection. Some web servers close connections because the client IP address or hostname is unauthorized or is a known malicious client. Other identification techniques can also be used.

Client Hostname Identification

Most web servers can be configured to convert client IP addresses into client hostnames, using “reverse DNS.” Web servers can use the client hostname for detailed access control and logging. Be warned that hostname lookups can take a very long time, slowing down web transactions. Many high-capacity web servers either disable hostname resolution or enable it only for particular content.

You can enable hostname lookups in Apache with the HostnameLookups configuration directive. For example, the Apache ...