Discovering DHCP linux device

Hi,

I have built a small linux machine that I take with me to work on
customer's sites, but one thing I would like is a way to detect the
machine on their network.

If I were the systems administrator there, I could go through the DHCP
server logs and find it. But I'm not, and it just seems a little
unprofessional to have to ask for help to find my own hardware.

I know I could sniff the traffic and look for DHCP transactions, but
this is (by and large) a one time event which means I have to be
watching while the thing comes online. And it is again a little
unprofessional as it is quite cumbersome to be poring through sniffer
data to find my own hardware.

What I would do is write a script with netcat that broadcasts the
device's presence periodically, and have another application on my
laptop to listen for these broadcasts. As long as we're on the same
LAN I should be able to detect those broadcasts, and then I will know
the IP to manage the machine.

I can create this script, but I'm posting this to see if there are any
linux projects already underway that meet my requirements. I know
that my NAS (Infrant) uses a similar approach to managing those
systems, so something like that would do the trick.

Thanks,

Paul

On Dec 17, 3:03 pm, thewozza <paulwoz...@gmail.com> wrote:
> Hi,
>
> I have built a small linux machine that I take with me to work on
> customer's sites, but one thing I would like is a way to detect the
> machine on their network.
>
> If I were the systems administrator there, I could go through the DHCP
> server logs and find it. But I'm not, and it just seems a little
> unprofessional to have to ask for help to find my own hardware.
>
> I know I could sniff the traffic and look for DHCP transactions, but
> this is (by and large) a one time event which means I have to be
> watching while the thing comes online. And it is again a little
> unprofessional as it is quite cumbersome to be poring through sniffer
> data to find my own hardware.
>
> What I would do is write a script with netcat that broadcasts the
> device's presence periodically, and have another application on my
> laptop to listen for these broadcasts. As long as we're on the same
> LAN I should be able to detect those broadcasts, and then I will know
> the IP to manage the machine.
>
> I can create this script, but I'm posting this to see if there are any
> linux projects already underway that meet my requirements. I know
> that my NAS (Infrant) uses a similar approach to managing those
> systems, so something like that would do the trick.
>
> Thanks,
>
> Paul

Okay so I got impatient and just ended up writing my own stuff. It
isn't pretty, but I can output periodic broadcasts with netcat on my
headless linux device, and I have a reasonably cumbersome method of
capturing and parsing the data from tshark on my laptop. So now I can
show up and be confident that I can find my hardware without having to
go through too many hoops.

RADAR-ADVERTISE.pl
#!/usr/bin/perl

$interval = 10; # defines the broadcast period in seconds

# open netcat as a filehandle
open (FILE, "|nc -b -u 255.255.255.255 9999 -p 9999");

# mark the NC filehandle as hot, so we're not buffering the output
{ my $ofh = select FILE;
$| = 1;
select $ofh;
}

# go forever! because I can't think of any good reason to stop
# it would probably be better to kill the loop and move this into a
cronjob if you're doing it once a minute
while (1) {
print FILE "LOOK IT IS ME!\n";
sleep $interval;
}

exit 0; # clear memory on exit

RADAR-DETECT.pl
#!/usr/bin/perl

# use tshark to grab data from the network port. we're watching for
udp port 9999 and IP broadcast
# this is very flexible, I used both vectors to ensure that most real
network data is filtered out
# you probably need to be root to sniff with tshark - sorry
# if being root is a big deal for you, you could probably use netcat
to grab the data
open (FILE, "tshark -l -R \"ip.dst == 255.255.255.255 and udp.dstport
== 9999\"|");

while (<FILE>) {
chomp;
$_ =~ s/^\W*//; # whitespaces are bad
($tdata, $source, $cruft) = split / /, $_;
print "$source\n"; # print the source IP of the device broadcasting
}

exit 0;

thewozza wrote:
> Hi,
>
> I have built a small linux machine that I take with me to work on
> customer's sites, but one thing I would like is a way to detect the
> machine on their network.
>
> If I were the systems administrator there, I could go through the DHCP
> server logs and find it. But I'm not, and it just seems a little
> unprofessional to have to ask for help to find my own hardware.
>
> I know I could sniff the traffic and look for DHCP transactions, but
> this is (by and large) a one time event which means I have to be
> watching while the thing comes online. And it is again a little
> unprofessional as it is quite cumbersome to be poring through sniffer
> data to find my own hardware.
>
> What I would do is write a script with netcat that broadcasts the
> device's presence periodically, and have another application on my
> laptop to listen for these broadcasts. As long as we're on the same
> LAN I should be able to detect those broadcasts, and then I will know
> the IP to manage the machine.
>
> I can create this script, but I'm posting this to see if there are any
> linux projects already underway that meet my requirements. I know
> that my NAS (Infrant) uses a similar approach to managing those
> systems, so something like that would do the trick.
>
> Thanks,
>
> Paul

A different way to look at it might be to stick an lcd on the device
so it can display it's ip.

http://www.seetron.com/slcds.htm
http://www.hobbyengineering.com/H2078.html

> I have built a small linux machine that I take with me to work on
> customer's sites, but one thing I would like is a way to detect the
> machine on their network.

If you know the network's IP range, then `nmap' should have no trouble
finding your device.


Stefan