Links Related to Firewalls

Nmap. Nmap is a popular port scanner allowing detection of some firewalls. This is freeware supplied with the source code. The product's site also contains lots of technical information. Available at http://www. insecure .org/nmap/ .
Firewalk . This is a freeware tracing utility based on TCP/UDP and a packet's TTL, allowing it to trace the network and bypass a firewall. It is available at http://www.packetfactory.net/firewalk Before using, you should become acquainted with the technical documentation available at http://www.packetfactory.net/firewalk/firewalk-final.pdf .
Hping. This utility organizes scanning through a dumb host. This freeware utility is well-documented and is a powerful tool for investigation of an internal network protected by a firewall. Available at http://www.hping.org/papers.html .
SSH client. This client is a freeware tool that can be used by corporate network users for bypassing limitations implied by the firewall protecting the internal network. The tool is supplied with the source codes and can be downloaded from http://www.openssh.com .
"Internet Firewalls: Frequently Asked Questions." This is a detailed FAQ about firewalls, available at http://www.interhack.net/pubs/fwfaq/firewalls-faq.pdf .
"Firewall." This is a synopsis of lectures about firewalls by Professor Yeali S. Sun (Taiwan). Available at http://www.im.ntu.edu.tw/~sunny/pdf/IS/Firewall.pdf .
OpenNet. This is a vast portal related to various issues of the network security. Along with other materials, it contains information about security holes in most popular firewalls. Articles are written in Russian and English. Available at http://www.opennet.ru .