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IP conflicts

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  • 03-11-2001 3:28am
    #1
    Hecate
    Registered Users Posts: 2,518 ✭✭✭


    there is some server/desktop/networked device in my college that is using the same ip as the netsoc server; with the result that the server is inaccessible for quite a lot during the day. We've tried in vain to find out who is using the address, but we know someone is because we can ping it even when the netsoc server is switched off.

    Now I thought once an ip address was assigned that it could not be used at all by somthing else, and this would have no effect on the machine that was originally using it.

    Are there any tools or scanners out there that will allow us to find out what exactly is using this ip?, or somthing we can do to our server to ensure it retains it's ip (it's a FreeBSD 4.4 server) ?


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    #2
    seamus
    Registered Users Posts: 68,317 ✭✭✭✭seamus


    the command ping -a aaa.bbb.ccc.ddd should tell you the name of the computer, and if your network manager is any good :p that should tell you where it is. i.e. in UCD, a computer named CSB02B3PC6 means 'Computer Science, room B.02, bench 3, pc 6'. Failing that try a tracert, but it all depends on whether your network allows ping,etc. commands to be send over the network. That's all I can suggest :)


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    #3
    Hecate
    Registered Users Posts: 2,518 ✭✭✭Hecate


    yeah we've tried pinging and tracerouting it; but it resolves the ip from our hostname (netsoc.kst.dit.ie) anyway.


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    #4
    The Cigarette Smoking Man
    Closed Accounts Posts: 649 ✭✭✭The Cigarette Smoking Man


    Shut off your server and ARP the ip address. Then if you have Cisco switches with ip accounting enabled you can use the command:

    sh interfaces mac

    That'll tell you which port the other device is using.


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    #5
    Hecate
    Registered Users Posts: 2,518 ✭✭✭Hecate


    we have a suspicion that ip addresses may be bound to mac addresses within the college so you can't just go and grab an ip at will, has anyone heard of this being done before?, and of ways around it?


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    #6
    The Cigarette Smoking Man
    Closed Accounts Posts: 649 ✭✭✭The Cigarette Smoking Man


    What subnet mask are you using on your LAN? If they've configured the network correctly* you'll be able to track it down to a subnet and then narrow it down to the switch etc.

    *I'm sure they haven't - I went to DIT.

    OT: A CCIE told me once that you should never use a mask greater than /25 on your end user segments to keep network broadcasts to a minimum.


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    #7
    Bosco
    Closed Accounts Posts: 219 ✭✭Bosco


    Heya Hecate,

    If your college is using DHCP (very probably) or BOOTP (unlikely) to dynamically assign IP addresses to machines, then yes, each machine will be assigned a unique IP address. Servers will probably have their IP address assigned to them manually, and the DHCP server will (should) be setup not to assign these reserved server IP addresses to any machines.

    However, there is nothing stopping someone manually assigning an IP address to a machine and putting it on the network. Fortunately this usually requires admin. priviliges on the machine in question(NT or UNIX), so it can't be done by just anyone.

    Hope this helps,

    Bosco


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