The LARTC-HOWTO describes many advanced ways of routing and shaping traffic. Using the HOWTO, you will be able to shape traffic in myriad ways, which will help you lower latency for interactive use when others are downloading or uploading. It will also teach you how to limit certain hosts/protocols' bandwidth usage. It also explains many aspects of routing using the 'ip' tool from the iproute2 suite.
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 Linux Virtual Server Project is a project to cluster many real servers together into a highly available, high-performance virtual server. The LVS load balancer handles connections from clients and passes them on the the real servers (so-called Layer 4 switching) and can virtualize almost any TCP or UDP service, like HTTP, HTTPS, NNTP, FTP, DNS, ssh, POP3, IMAP4, SMTP, etc. It is fully transparent to the client accessing the virtual service.
Heartbeat is a full-function high-availability system for Linux and other POSIX-like OSes. It monitors services and restarts them on errors. When managing a cluster (more than 1 machine), it will also monitor the members of the cluster and begin recovery of lost services in less than a second. It runs over serial ports and UDP broadcast/multicast, as well as OpenAIS multicast. It is easily adapted to different interconnect media and protocols. When used in a cluster, it can operate using shared disks, data replication, or no data sharing. Versions starting with 2.0 are comparable to any commercial HA package, providing resource monitoring, larger clusters, and detailed dependency information.
log_analysis is a log file analysis engine that extracts relevant data for any of the recognised log messages and produces a summary that is much easier to read. It can be configured to recognize entirely new log types. log_analysis natively understands about 100 different kinds of syslog messages, as well as sulog and wtmp messages for Linux, Solaris, and OpenBSD. It also has optional continuous monitoring capabilities, with both text and GUI modes.
Mason is a tool that interactively builds a firewall using Linux' ipfwadm or ipchains firewalling. You leave mason running on the firewall machine while you are making all the kinds of connections that you want the firewall to support (and want it to block). Mason gives you a list of firewall rules that exactly allow and block those connections. It can either build a firewall from scratch for you or supplement an existing firewall.
MAT is an easy-to-use network-enabled UNIX configuration and monitoring tool. It provides an integrated tool for many common system administration tasks, including backups, replication, and running commands on hundreds of machines at once. It includes a warning system for potential system problems, and graphing of many common system parameters. MAT provides many of the tools a system administrator needs during the day, including DNS, NIS, Backups, and Replication. One can run a MAT command on many hosts at once. A simple editor window is provided which can modify a set of machine's configurations in one session.