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.
Fd Linux is a mini floppy distribution of Linux set to fit on 1 floppy disk (kernel and root fs are combined). The sole purpose of this floppy distribution is to provide new Linux users with low-end machines (such as a 386) a very useful set of networking related binaries that can be easily accessed at any time, and which can be used in almost any networked environment (libraries, colleges, offices, small home LANs, dorm rooms, etc.).
Firewall is a set of scripts (firewall, fwup, and fwdown) that implement an ipchains firewall and various forms of network address and port translation. All you have to do is read the policy file and edit it to reflect your topology and filtering policy. It supports many different types of network topology (single host, traditional forwarding, masquerading, port forwarding, alias port forwarding and NAT), up to 10 untrusted interfaces each with their own policy, and over 50 network applications. It also supports centralised administration of multiple remote firewalls (meta-firewall).
Linux FreeS/WAN provides IPSEC (IP Security, which is both encryption and authentication) kernel extensions and an IKE (Internet Key Exchange, keying and encrypted routing daemon) as well as various rc scripts and documentation. It is known to interoperate with other IPSEC and IKE system already deployed by other vendors such as OpenBSD, Cisco, or CheckPoint. It also features Opportunistic Encryption, subnet extrusion, and with the appropriate patches interops nicely with Microsoft Windows XP/2000 using X.509 certificates.
The IP Masquerade HOWTO is the document that contains instructions on understanding, configuring, and troubleshooting NAT or Network Address Translation for Linux. It covers topics such as IPTABLES, PORTFW, IPCHAINS, IPFWADM, stronger packet firewalls, multiple network segments, and configuring many client operating systems. It also has an extensive FAQ and troubleshooting section.
Fireflier is a firewall tool which is built on top of the iptables framework. It allows you to create rules based on single incoming network packets or to simply allow/deny single packets to pass. It features a client-server approach for administering from another PC, SSL connection between client and server, rules with timeouts (rules are deleted after some time or when fireflier-server shuts down), and filtering based on applications.
Mail2sh makes it possible to carry out shell commands by email. Email is sent to a particular user on your host and the commands will be carried out if the user and password given matches ones in /etc/passwd. Commands are executed with the user's privileges, and combined with a PGP module ensures a certain level of security for use. Note that the system is not natively encrypted, so use of an encryption mechanism is highly recommended for security reasons.