How do I find out which devices are on a network?
For the first scenario, look at nmap. You can scan entire subnets in one command. For example: nmap -sP 192.168.0.1/24
For the second, the router IP should show up as the gateway IP for your machine. In windows, that appears in the connection status dialog.
You can ping to the broadcast address and see arp table. Here is a example of doing it on Linux:
ping -b 192.168.1.255
arp -n
NB: The OS of the device have to echo back to ICMP echo request. Some OS don't reply to ICMP with broadcast IP adress. In which case you can ping to every possible ip address in the network. Recently windows boxes don't reply to ICMP echo with unicast IP address by default, so this won't help.
Angry IP Scanner is an awesome tool for this.
It will also allow you to export a .csv for use in IP inventory etc.
I use The Dude.
I found it here yesterday when looking for network tools. Run it on your machine and it makes a map of all equipment on your network. The best part is that it's totally free!
In response to the second question:
On Windows
- Windows Key + R
- Type in cmd
- At the prompt type in "ipconfig"
The output should have a line that lists the Default Gateway. There might be more than one adapter listed, but typically only one with an ip address and default gateway listed.