Discovering DHCP linux device - Networking

This is a discussion on Discovering DHCP linux device - Networking ; 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 ...

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Thread: Discovering DHCP linux device

  1. 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

  2. Re: Discovering DHCP linux device

    On Dec 17, 3:03 pm, 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


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

    exit 0;

  3. Re: Discovering DHCP linux device

    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

  4. Re: Discovering DHCP linux device

    > 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

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