September 2003
Intermediate to advanced
304 pages
8h 39m
English
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Quickly Poll Wireless Clients with ping
A quick and dirty method for determining who is on your local subnet.
This is a simple, quick hack, but useful in many circumstances. Suppose you are associated with a wireless network, and are curious about who else is also using the network. You could fire up a network sniffer (like Ethereal [Hack #38] or tcpdump [Hack #37]), or manually scan for associated clients (using nmap [Hack #40]), although that might be construed as antisocial. You’re not so much interested in what people are doing, just how many people are online.
It is simple to find clients on your local network using the ubiquitous ping utility. Simply ping the broadcast address of your network, and see who responds.
You can find the broadcast address by running ifconfig like so:
rob@florian:~$ ifconfig eth0
eth0 Link encap:Ethernet HWaddr 00:40:63:C0:AA:4B
inet addr:10.15.6.1 Bcast:10.15.6.255 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:13425489 errors:0 dropped:33 overruns:0 frame:0
TX packets:19603221 errors:1118 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:100
RX bytes:3073225705 (2930.8 Mb) TX bytes:1301320438 (1241.0 Mb)
Interrupt:10 Base address:0xe800There it is, the Bcast address. This is the
broadcast address for your local subnet, which every machine is
listening to. In Mac OS X and BSD, it is simply listed as the
broadcast address:
rob@caligula:~$ ifconfig en1 en1: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> ...Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
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O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.