Handy Network Utilities: nast, fping

I discovered a wonderful utility last night: nast. I wanted to scan my local network, just to see what devices were on it, what their addresses were, etc. I could ping my entire subnet, but what if I had a machine that rejected ICMP packets? (Not that I do very often, but it can happen in larger environments). I thought using a protocol like ARP would be much more robust, since it is pretty much guaranteed to be available. Then I discovered nast.

nast can do a lot of neat things. The first I found was mapping a subnet of course, which you can do by running

sudo nast -i eth1 -m

adjusting the interface to fit. It will return something like:

Nast V. 0.2.0

Mapping the Lan for 255.255.255.0 subnet ... please wait

MAC address             Ip address (hostname)
===========================================================
00:19:D2:92:20:CE       192.168.1.1 (MyGateway)
00:1B:C0:B7:86:CB       192.168.1.2 (MyBox) (*)
00:14:38:E5:76:10       192.168.1.5 (SomeOtherBox)

nast can also try to find out if there are any nodes on your subnet acting in promiscuous mode, which I think is pretty hot. Check out the main nast page for the full feature set.

In my searching, I also came across fping. Its main improvements over regular old ping are:

• More than one host can be passed (as well as a file containing hosts)
• Its output is very simple and easy to parse, making it ideal for scripting
• It tries each host and moves on if there is no response, making the whole process faster

Instead of

ping -c 1 myhost1 ; ping -c 1 myhost2

you can just run

fping myhost1 myhost2

which just returns

myhost1 is alive
myhost2 is alive

Both nast and fping are available in the Ubuntu repos.