Who Else is Using My Router, How to Check

[nujinini]

Well, I'd still recommend going to the wireless router itself and looking for logs on it for information regarding DHCP and/or connection attempts.

If you're lucky, the router will support rsyslog - which basically means you configure it with an ip address (that of your linux machine) and it will forward the syslog messages to your Linux machine's rsyslog server. You'll have to configure this on the linux server, too, but it is a simple two-line edit of one file.

Now, if you just want to do a network scan, which will report any devices found with an ip address on that network, this is simple, too. Nmap is a good way to do this, e.g.:

nmap -n -sP 192.168.1.0/24

This will just do a ping scan (versus also looking for open ports, which would take longer) of the network given. If run as root, it will also display the associated MAC addresses - handy for identifying a specific computer...

This one worked for me.

jun@jun@ldme ~ $ nmap -n -sP 192.168.1.0/24

Starting Nmap 5.21 ( Nmap - Free Security Scanner For Network Exploration & Security Audits. ) at 2011-09-30 15:28 PHT
Nmap scan report for 192.168.1.1
Host is up (0.0033s latency).
Nmap scan report for 192.168.1.4
Host is up (0.00014s latency).
Nmap scan report for 192.168.1.7
Host is up (0.065s latency).
Nmap done: 256 IP addresses (3 hosts up) scanned in 2.61 seconds
jun@jun@ldme ~ $

Would it be possible to check on each machine re their websites and activities?

[atreyu]

Not directly, there's no magic Linux command to do that. You need to set up some sort of DNS proxy inb/t the clients and your router to do that. You could do that w/your Ubuntu box - make it a kind of dedicated internet proxy. There are specific tools and even full-on Linux distros for this, but I'm no pro at it, I hope others will chime in to help you.

For comprehensive-oriented solutions, I can tell you that I've heard good things about Untangle and Dans Guardian for this kind of thing, though.

[sgosnell]

Read this page for a detailed list of network monitoring tools. Also investigate tcpdump.