The Ethical Hacker Network - Network keeps crashing (nmap)

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Kajjan

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Network keeps crashing (nmap)

« on: January 09, 2012, 08:47:26 PM »

Greetings.

This is my first post here on EHN. Feels great to be here!

I ran into a problem while trying to scan my entire local network using nmap.

I am running nmap on a virtual machine using VMware (linux - Backtrack 5 r1)
VMware network settings on NAT

I also run Windows Xp sp2 virtually as a Target machine
Wmvare network settings on Host-only

Host is a windows 7 computer connected to a NETGEAR router and so on.

The script went something like this
" nmap -vv -F -T5 -sn 111.222.*.* "

And after about 50 seconds the network connection goes down.
I have to restart modem and router and then run ipconfig /renew to get the
internet connection back up again. Tried several times but i got disconnected every time.

Why does the connection go down ?

Thank you for taking your time reading my post


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doodleface

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Re: Network keeps crashing (nmap)

« Reply #1 on: January 09, 2012, 09:14:54 PM »

Try this command " nmap -vv -F -T4 -sn 111.222.*.* "

The problem here is the setting T5 tells nmap to send packets almost as fast as the network adapter can send them. This overloads your netgear router and causes a Denial of Service via the ping scan.


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Kajjan

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Posts: 2

Re: Network keeps crashing (nmap)

« Reply #2 on: January 10, 2012, 07:14:08 AM »

You were right. It works now. Thank you very much. I did not realize that the scan was powerful enough to do that to my network.
lesson learned.

Peace


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MaXe

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I've just upgraded myself to a cyborg muahahaa!!1

Re: Network keeps crashing (nmap)

« Reply #3 on: January 10, 2012, 11:57:01 AM »

I was going to say the same as doodleface, as some routers even has builtin firewalls that looks at the traffic, and sometimes nmap sends malformed traffic (according to the router), which in return, drops packets or suddenly all packets.

When I haven't had any router devices and scanned, I didn't experience any problems except using T5 (aka "Insane"?) over the Internet is generally a bad idea. T5 can work on LAN's but over the Internet and generally, T4 is better to use. T3 is default.