Arno's IPTABLES Firewall Script is a secure stateful firewall for both single and multi-homed machines. It supports NAT and SNAT, port forwarding, ADSL ethernet modems with both static and dynamically assigned IPs, MAC address filtering, stealth port scan detection, DMZ support, protection against SYN/ICMP flooding, experimental IPv6 support, multi-interface/aliased-IP support, and extensive user definable logging with rate limiting to prevent log flooding. It has plugin support to add extra features (like SSH Brute Force protection and (Racoon) IPSEC support). It is easy to configure and highly customizable. A filter script that makes your firewall log more readable is also included.
fwknop implements an authorization scheme called Single Packet Authorization that requires only a single encrypted packet to communicate various pieces of information, including desired access through an iptables, ipfw, or pf firewall policy and/or specific commands to execute on the target system. The main application of this program is to protect services such as SSH with an additional layer of security in order to make the exploitation of vulnerabilities much more difficult. The authorization server works by passively monitoring authorization packets via libpcap. Also supported is a robust port knocking implementation based around iptables log messages.
FrazierWall Linux is a single floppy distribution Linux firewall that is based on the Linux Router Project. It is designed for use with ethernet base internet connections (such as cable modems or xDSL lines). It allows you to share such a connection with several other computers on a LAN. It is easy to setup and maintain, and is available in a Linux configurable software version.
Astaro Portscan Detection is a netfilter target which will attempt to detect TCP and UDP port scans and log them to syslog. This target is based upon Solar Designer's scanlogd. It suppports mutliple levels of logging, custom prefixes for entries, weighted total port scan detection, and port scan temporal spread detection.
Harm acts as a four-way socket redirector that allows you to effectively make a TCP connection from the Internet to a host behind a Linux masquerade-style firewall. The server (behind the firewall) makes connections to the client (on the Internet). After a successful connection, it will bounce packets from a telnet client (Windows and Linux) to the Harm client, to the Harm server (Linux only), or to the telnet daemon behind the firewall.
rc.firewall is configurable for dialup and static IP addresses. It is based on Linux-kernel 2.4.x, and it generates it's own configuration file. It supports specific port filtering for the internet- , intranet-, and a dmz-zone. For the DMZ-Zone, there is also a machine-specific port filtering, and redirection of specific ports of the internet-interface available. Note: Do not install this in productive environments, until you have checked the rules/tables with your own eyes.
Perl Advanced TCP Hijacking is a collection of tools for inspecting and hijacking network connections written in Perl. It consists of a packet generator, an RST daemon, a sniffer, an ICMP redirection tool, an ARP redirection tool, an IDS testing tool, and an automatic hijacking daemon for plain protocols, and features both GUI and terminal interfaces.