Javvins Network Security Library
http://www.javvin.com/networksecurity/

Network Dictionary: Networking Articles and Whitepapers
http://www.networkdictionary.com/

MIS Training Institute
http://www.misti.com/

Network Security Portal
http://www.infosyssec.com/

Security Specific Information Resource
http://www.searchsecurity.com/

Network Security Portal
http://www.securitynewsportal.com/

Security for Linux World
http://www.linuxsecurity.com/

The Encyclopedia of Computer Security
http://www.itsecurity.com/

Sans Institute Security Glossary
http://www.sans.org/resources/glossary.php

TechTarget's Network Security Glossary
http://whatis.techtarget.com/definitionsCategory/0,289915,sid9_tax1683,00.html

TechWeb Encyclopedia
http://www.techweb.com/encyclopedia/

MRTG - Multi Router Traffic Grapher
http://www.mrtg.org/

NTOP - Networktraffic probe to show network usage
http://www.ntop.org/ntop.html

Ethereal Packet Sniffer
http://www.ethereal.com/