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Network Security

Posted on 2008-10-21
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I resently had a Network Admin leave the company. I wanted to know what is the best way to check our Network Security to make sure there are not backdoors open for him to access our network.  Are there any tools I can use to check our external access to our LAN?

Thank you,
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Question by:KappaMan1911
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by:Rartemass
ID: 22772183
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by:KappaMan1911
ID: 22772304
I have Wire Shark, but I have never really learned who to use it.  I will check out all of your surgestions.  I was told it is not a good idea to leave wireshark on a server.  thanks.
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larsga earned 1500 total points
ID: 22772397
"We let the janitor go, how can we be certain that he can't get into the apartment block again?" Apologies for sounding facetious, but that's more or less the physical analogy of your question. Without knowing more about the network and what you want to protect, I can only give some general advice.

You could do the following (listed in increasing level of paranoia):

- Change locks on doors and windows.
In other words, disable accounts or change passwords on equipment/systems/accounts he had access to. Ranging from Windows user accounts to administration passwords on network gear. If you have VPN set up (access to your network from remote offices / home / people travelling with laptops), change the VPN passwords.

- Check if any windows are left ajar.
The most obvious thing to check would be the configuration on the firewall(s)/router(s) that face the Internet. You could use 'nmap' or a similar portscanner on the external IP address of the Internet firewall to see of he left an open port (although the output from a portscan wouldn't tell you much unless you know something about networking).

- Look for any hidden windows in the attic or floor-boards that are loose.
If he is competent and really wanted to hide a backdoor, there is really no way you can be absolutely sure without a total cleaning and reinstalling everything. For example, he could have left a small router on the network that is set up to be accessible from dial-up/ISDN/cell-phone; or perhaps a small program on a PC that would connect to him at 1:00AM every second saturday.
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by:KappaMan1911
ID: 22772549
He was a new Network Admin... So I did not give him the keys to the kingdom.  He had not access to the Firewalls, routers., or VPN, and I have changed all those passwords.  Your point is well taken.  Moving forward I will strenghen my network monitoring and security.  Thank you for the advice.
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