Some good documents regarding TCP/IP for linux can be found all over the web, but how to access it when you cant connect?
Linux Tutorial - Linux Network Administration

This tutorial covers TCP/IP networking and system configuration basics. Linux can support multiple network devices. The device names are numbered and begin at zero and count upwards.

XS4ALL
De hoeveelheid dataverkeer uitgedrukt in datapakketten die XS4ALL in totaal heeft vervoerd sinds: 5 september 2005 (meer dan 5000 cd's). Dus bezwaarplicht.nl en stopdebewaarplicht.nl. En eerstdenkenvoorjeeenwetbedenkt.nl.

An Illustrated Guide to IPSecNot up to the classic TCP/IP illustrated but far better than cisco's peter packet

IPSec is a suite of protocols for securing network connections, but the details and many variations quickly become overwhelming. This is particularly the case when trying to interoperate between disparate systems, causing more than one engineer to just mindlessly turn the knobs when attempting to bring up a new connection.

I used to be a [netmaster] but nowadays I'm not into TCP/IP anymore, still TCP/IP Tutorial and Technical Overview is a good read for those who want to bluff their way into the internet.

From Chris Shiflett The Truth about Sessions

Nearly every PHP application uses sessions. This article takes a detailed look at implementing a secure session management mechanism with PHP. Following a fundamental introduction to the Web's underlying architecture, the challenge of maintaining state, and the basic operation and intent of cookies, I will step through simple and effective methods that can be used to increase the security and reliability of your stateful PHP applications.

It is a common misconception that PHP provides a certain level of security with its native session management features. On the contrary, PHP simply provides a convenient mechanism. It is up to the developer to provide the complete solution, and as you will see, there is no one solution that is best for everyone.