How to find out how many computers on the network

C

ColdFlare

Limp Gawd
Joined
Aug 31, 2001
Messages
382
Heres my situation:

I am currently running a network with my cousin who lives right above me. We have a wire running out my window up to his.. its ethernet cat 5.

Now a friend of his has just moved into my home and he lives in another room. They are good friends I guess, but I do not like him. I do not want his computer hooked onto my network. Is there anyway for me to check if he has hooked up a router to my cousins room and run extra cat 5 into his room?

What I want to do is find out if hes actually using my network. I can just change the ips, but he goes into my cousins room all the time, so he can check the ip.

Anyhelp would be greatly appreciated, thanks.
 
If you have a soho router (linksys, smc, dlink), most will display which ip's have been taken from the dhcp. This is probably the most common way of figuring it out.

On the newer routers, you should be able to allow traffic by MAC address. This way you could only allow your pc and your cousin's mac addresses.
 
Originally posted by Darthkim
This way you could only allow your pc and your cousin's mac addresses.
Click to expand...
Unless his friend figures this out and starts spoofing MACs :)
 
Something like What's Up? Gold might do the trick. Do a ping scan on the known IP range and it'll return a list of all active IPs. A simple scan is really all that would be required.
 
...or you can fire up your favourite network monitor (this for example), and look for Browser announcemts and ARP requests...
 
Originally posted by axdx
...or you can fire up your favourite network monitor (this for example), and look for Browser announcemts and ARP requests...
Click to expand...

This is the best suggestion.

DHCP works...until he specifies an IP in the range.

MAC filtering works...until he spoofs.

But monitoring the actual network traffic is the way to go.
 
Why don't you walk up stairs and bitch slap him?

Why fight him over the wire when he's 50 feet away?

:D
 
http://www.famatech.com/download/

See the bottom of the page in "Free network utilities"

Download IP address scanner ...

This will scan your subnet, and show you all the computers including ip address, hostname, and other netbios stuff

Fast and easy and even more informations that only how much
 
If your useing DHCP, only use a range of 2 IP's

Assign 1 for the ineternet shareing machine (which should be yours!) and that leaves 1 spare, if he cant be assigned an ip, he cant get on!
 
Originally posted by Digital-Vortex
If your useing DHCP, only use a range of 2 IP's

Assign 1 for the ineternet shareing machine (which should be yours!) and that leaves 1 spare, if he cant be assigned an ip, he cant get on!
Click to expand...

unless his cousin sets up a router or acts as an internet connection sharing machine, and NAT's the other guy.
 
http://www.nmapwin.org/

Several other people have mentioned it. It is a full featured version of nmap which will let you find anything sitting on your network.

After that, I would ratch down your DHCP scope and restrict access by MAC address. Or.. go upstairs and do some interpersonal network auditing ;)
 
Man.. the people here simply amaze me at the lengths they'll go. I have a different approach:

1) You called the place 'my home'. Are you the owner? If so put that foot down now.

2) Move the network to static IP. Disallow traffic from ALL IPs. Then start poking holes and letting traffic in (On an IP by IP basis). It would take that guy quite a while to figure out what you did. If he does figure it out he can con your cousin into letting him use the IP he has. Next thing after that is to give your cousin the boot.

3) If this guy did something stupid like plug a ROUTER into the network and setup NAT/Firewalling.. it would do him no good. He won't be able to connect to the net as your router doesn't know about his network so it will just drop packets destined for it. If he were smart (I doubt he is) then he'd know of a way around this.
 
But if he installed a router and gave it one of the two allowed ip's, the first router would just see everything as traffic from the one allowed ip not knowing about the equipment behind it. It would care as long as it's from one of the two allowed ip's. It's up to the second router to route the traffic from there.

I would also go the manual approach, your house, you make the rules. Why is a guy you don't even like moving into the same house?

Also, maybe you could firewall him off and charge him for net access. That way, at least you'd be making money off of him. You could use m0n0wall etc and put him in the dmz so he could have net access but nothing else.
 
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