Finding other computers on network over command line

Question

I've got a handful of Macs on my home network, and shell access to only one of them from the outside. How can I figure out what IP address of the other machines are?

Answer 1

Maybe it's a bit of overkill but you could use nmap

Answer 2

A quick CLI one liner to step through /24 subnet ping each IP address. Quick and kind of dirty, but it works.

for (( x=1; x <= 254; x++ )); do ping -c 3 192.168.0.$x; done

Explanation: To change the range, change x=1 to x=130, or whatever you want to start at, and 254 to the end, say 135.

for (( x=130; x <= 135; x++ ));

ping -c 3 is send three pings. To change the number of pings change the 3 to something else, and to change the address range, change the 192.168.0 to something else.

do ping -c 30 10.10.0.$x;

Answer 3

Try arp -a to see your computer's current arp table. It will show only those IP addresses your computer has interacted with. Output like this (obscured a little to hide MAC addresses on my network):

$ arp -a
? (10.1.168.1) at xx:xx:9e:82:ab:f6 on en1 ifscope [ethernet]
? (10.1.168.16) at xx:xx:29:d3:17:8 on en1 ifscope [ethernet]
? (10.1.168.115) at xx:xx:2:4f:76:14 on en1 ifscope [ethernet]
? (10.1.168.131) at xx:xx:6b:d0:36:a5 on en1 ifscope [ethernet]
? (10.1.168.134) at (incomplete) on en1 ifscope [ethernet]
? (10.1.168.137) at xx:xx:65:46:cd:b8 on en1 ifscope [ethernet]
? (10.1.168.255) at ff:ff:ff:ff:ff:ff on en1 ifscope [ethernet]
? (192.168.4.255) at ff:ff:ff:ff:ff:ff on vmnet8 ifscope [ethernet]
? (192.168.110.255) at (incomplete) on vmnet1 ifscope [ethernet]

If you don't have further information on which computer is which, you can gain a little more information by identifying the manufacturers of the network cards through MAC address lookup.

Answer 4

Assuming all the other machines are in the same broadcast domain as the one to which you have access, pinging the broadcast address will often suffice. It will not find machines that are asleep, nor those configured to not respond to pings, nor those that will respond to pings but not to broadcast pings.

% ifconfig -a | grep broadcast
        inet 192.168.1.241 netmask 0xffffff00 broadcast 192.168.1.255
% ping -i 5 -c 2 192.168.1.255
PING 192.168.1.255 (192.168.1.255): 56 data bytes
64 bytes from 192.168.1.241: icmp_seq=0 ttl=64 time=0.393 ms
64 bytes from 192.168.1.254: icmp_seq=0 ttl=255 time=2.511 ms (DUP!)
64 bytes from 192.168.1.65: icmp_seq=0 ttl=64 time=5.810 ms (DUP!)
64 bytes from 192.168.1.255: icmp_seq=0 ttl=64 time=7.886 ms (DUP!)
64 bytes from 192.168.1.241: icmp_seq=1 ttl=64 time=0.312 ms

--- 192.168.1.255 ping statistics ---
2 packets transmitted, 2 packets received, +3 duplicates, 0% packet loss
round-trip min/avg/max/stddev = 0.312/3.382/7.886/3.010 ms

The first and last response will almost always be your local machine. The (DUP!) responses are from other machines (though this example also show some machine responding with the broadcast address itself, which is not terribly useful).

You might also try the all-ones broadcast address:

% ping -i 5 -c 2 255.255.255.255
PING 255.255.255.255 (255.255.255.255): 56 data bytes
64 bytes from 127.0.0.1: icmp_seq=0 ttl=64 time=0.392 ms
64 bytes from 192.168.1.254: icmp_seq=0 ttl=255 time=3.053 ms (DUP!)
64 bytes from 192.168.1.65: icmp_seq=0 ttl=64 time=8.685 ms (DUP!)
64 bytes from 127.0.0.1: icmp_seq=1 ttl=64 time=0.319 ms

--- 255.255.255.255 ping statistics ---
2 packets transmitted, 2 packets received, +2 duplicates, 0% packet loss
round-trip min/avg/max/stddev = 0.319/3.112/8.685/3.401 ms

This example shows less cruft. All the (DUP!)s are other machines and the local machine is easily identified as 127.0.0.1.

Answer 5

You could try using dns-sd in order to perform Bonjour queries on the LAN.

Answer 6

If you know the name of the other computers in the LAN, the simplest way is to ping them:

$ ping foobar

Pinging foobar.lan [192.168.0.25] with 32 bytes of data:

Reply from 192.168.0.25: bytes=32 time<1ms TTL=64
Reply from 192.168.0.25: bytes=32 time<1ms TTL=64

This may depend on your local router or DHCP server. If the bare hostname doesn't work, try appending .local (ie, ping hostname.local).

Obviously this doesn't work well for large LANs or people with poor memories.

Answer 7

If you're using Macs, (assuming 10.5 or greater,) just enable VNC for desktop access and use Flame.app.

http://husk.org/apps/flame/

It's a really nice little utility that gives you exactly what you need, really quickly. The only thing is that you would have to go farther than SSH.