Network security

[Chadley Wilson]

Hello friends,

My network with approx 300 users is routed to the internet through a
proxy and firewall, we have a DNS server and PDC Server.
It is a winXplease network.

With a linux PC connected -
What tools would you suggest I could use for the following:

1) Track an internal PC running a sniffer of some sort, obtain its ip
and mac address, then stop it sniffing and maybe kick it off the
network.

2) Be alerted when someone tries to sniff from outside, trace him and
obtain his details or ISP details.

I am terribly new to security, please teach me!
-- 
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Chadley Wilson
Soon 2 B RHCE
Linux Rocks
Welcome to my world.
Enjoy the adventures of Linux 
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Linux is easy, lazy people critise, curse and fail.