opensourcenet

With tools like STD Knoppix, you can easily document your Network by drawing a Network Diagram of your Enterprise. Monitoring a Proxy Server, a Network Administartor will be able to know the websites that local users are accessing. You can deny access to inappropriate websites.
On a Proxy Server,a Network Administrator can use drifnet to check the web behaviour of his users.

Nagios is a popular open source computer system and network monitoring software application. It watches hosts and services, alerting users when things go wrong and again when they get better.
    * Monitoring of network services (SMTP, POP3, HTTP, NNTP, ICMP, SNMP, FTP, SSH)
    * Monitoring of host resources (processor load, disk usage, system logs) on a majority of network operating systems, including Microsoft Windows with the NRPE_NT plugins.
    * Monitoring of anything else like probes (temperature, alarms...) which have the ability to send collected data via a network to specifically written plugins
    * Remote monitoring supported through SSH or SSL encrypted tunnels.
    * Simple plugin design that allows users to easily develop their own service checks depending on needs, by using the tools of choice (shell scripts, C++, Perl, Ruby, Python, PHP, C#, etc.)
    * Parallelized service checks available
    * Ability to define network host hierarchy using "parent" hosts, allowing detection of and distinction between hosts that are down and those that are unreachable
    * Contact notifications when service or host problems occur and get resolved (via e-mail, pager, SMS, or any user-defined method through plugin system)
    * Ability to define event handlers to be run during service or host events for proactive problem resolution
    * Automatic log file rotation
    * Support for implementing redundant monitoring hosts
    * Optional web-interface for viewing current network status, notifications, problem history, log files, etc.