• ip_dynaddr.txt - from the 2.4.14 kernel. A really short reference to the ip_dynaddr settings available via sysctl and the proc file system.

• iptables.8 - The iptables 1.3.1 man page. This is an HTMLized version of the man page which is an excellent reference when reading/writing iptables rule-sets. Always have it at hand.

• Ipsysctl tutorial - Another tutorial I have written about the IP System Control in Linux. A try to make a complete listing of all the IP variables that can be set on the fly in Linux.

• Policy Routing Using Linux - This is an excellent book that has now been opened up on the Internet regarding Policy routing in Linux. It is well written and most definitely worth buying. Written by Matthew G. Marsh.

• Security-Enhanced Linux - The official site of the Security-Enhanced Linux (SELinux) system developed as a proof of concept by the National Security Agency (NSA). SELinux is a fine grained Mandatory Access Control system, which lets you have a much higher control on who can do what and what processes has what privileges, et cetera.

• Firewall rules table - A small PDF document gracefully given to this project by Stuart Clark, which gives a reference form where you can write all of the information needed for your firewall, in a simple manner.

• http://l7-filter.sourceforge.net/ - The l7-filter project is basically a set of patches and files to make iptables and netfilter able to handle layer 7 filtering, mainly for QoS and traffic accounting. It works less reliably for filtering however, since it will allow the first couple of packets through before actually blocking traffic.

• http://www.netfilter.org/ - The official Netfilter and iptables site. It is a must for everyone wanting to set up iptables and Netfilter in linux.

• http://www.insecure.org/nmap/ - Nmap is one of the best, and most known, port scanners available. It is very useful when debugging your firewall scripts. Take a closer look at it.

• http://www.netfilter.org/documentation/index.html#FAQ - The official Netfilter Frequently Asked Questions. Also a good place to start at when wondering what iptables and Netfilter is about.

• http://www.netfilter.org/unreliable-guides/packet-filtering-HOWTO/index.html - Rusty Russells Unreliable Guide to packet filtering. Excellent documentation about basic packet filtering with iptables written by one of the core developers of iptables and Netfilter.

• http://www.netfilter.org/unreliable-guides/NAT-HOWTO/index.html - Rusty Russells Unreliable Guide to Network Address Translation. Excellent documentation about Network Address Translation in iptables and Netfilter written by one of the core developers, Rusty Russell.

• http://www.netfilter.org/unreliable-guides/netfilter-hacking-HOWTO/index.html - Rusty Russells Unreliable Netfilter Hacking HOW-TO. One of the few documentations on how to write code in the Netfilter and iptables user-space and kernel space code-base. This was also written by Rusty Russell.

• http://www.linuxguruz.org/iptables/ - Excellent link-page with links to most of the pages on the Internet about iptables and Netfilter. Also maintains a list of iptables scripts for different purposes.

• Policy Routing using Linux - The best book I have ever read on Policy routing nad linux. This is an absolute must when it comes to routing in linux. Written by Matthew G. Marsh.

• Implementing Quality of Service Policies with DSCP - A link about the cisco implementation of DSCP. This shows some classes used in DSCP, and so on.

• IETF SIP Working Group - SIP is one of the "next big things" it seems. Basically it is the defacto standards for Internet telephony today. It is horribly complex as you can see from the amount of documentation on the working groups homepage, and should hopefully be able to cope with pretty much any needs of session initiation in the future. It is used mainly to setup peer to peer connections between known users, for example to connect to [email protected] and setup a phone connection to that user. This is the IETF Working group handling all SIP work.

• IETF TLS Working Group - TLS is a transport layer security model that is one of the most common host to server based security mechanisms. The current version is running is 1.1 and work is ongoing to get 1.2 out the door with support for newer and better cryptos as of this writing. This is a standardized way of sending and receiving public keys for servers and handling trusted certificate agents etc. For more information, read the RFC's on this page.

• IPSEC Howto - This is the official IPSEC howto for Linux 2.6 kernels. It describes how IPSEC works in the 2.6 kernels and up, however, it is not the place to find out exactly how the Linux 2.2 and 2.4 kernels worked when it comes to IPSEC. Go to the FreeS/WAN site for that information.

• FreeS/WAN - This is the official site for FreeS/WAN, an IPSEC implementation for the Linux 2.2 and 2.4 kernel series. This site contains documentation and all necessary downloads for the IPSEC implementation. This effort has been discontinued due to several reasons discussed on the page, but efforts will still be put into bugfixes, documentation and the forums. For an IPSEC implementation for Linux 2.6 kernels, please look at the IPSEC Howto site and the information there.

• http://www.islandsoft.net/veerapen .html -Excellent discussion on automatic hardening of iptables and how to make small changes that will make your computer automatically add hostile sites to a special ban list in iptables .

• /etc/protocols - An example protocols file taken from the Slackware distribution. This can be used to find out what protocol number different protocols have, such as the IP, ICMP or TCP protocols have.

• /etc/services - An example services file taken from the Slackware distribution. This is extremely good to get used to reading once in a while, specifically if you want to get a basic look at what protocols runs on different ports.

• Internet Assigned Numbers Authority - The IANA is the organisation that is responsible for fixing all numbers in the different protocols in an orderly fashion. If anyone has a specific addition to make to a protocol (for example, adding a new TCP option), they need to contact the IANA, which will assign the numbers requested. In other words, extremely important site to keep an eye on.