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Thread: could be same ip on same network!!

  1. #1
    Just burned his ISO
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    Exclamation could be same ip on same network!!

    Hi there,
    i plugged my laptop to our domain network and then assigned an ip that iam using on another machine in my domain
    i did the following:

    ifconfig eth0 128.1.20..41 netmask 255.255.0.0
    <this ip am using on different pc>
    then >ifconfig eth0
    inet addr:128.1.200.41 bcast:128.1..255.255 mask:255.255.0.0

    how could be duplicate ip on the same network?

  2. #2
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    Default

    The IP could be the same because... Um... You made it the same?

  3. #3
    Super Moderator lupin's Avatar
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    Are you asking how you were able to assign a duplicate IP address to your laptop which is (presumably) running BackTrack?

    Its because Linux generally, and BackTrack specifically, wont prevent you from doing this. It makes a (possibly incorrect) assumption that you know what you're doing and won't assign an IP address that's already in use somewhere else on the same network.

    Or, are you instead asking how well a machine assigned a duplicate IP address will work where its network communications are concerned? Answer - probably not very well.
    Capitalisation is important. It's the difference between "Helping your brother Jack off a horse" and "Helping your brother jack off a horse".

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  4. #4
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    Default how if i set this ip to the DNS server?

    umm, thanks for the clarification lets say i set this manual ip same like the one with important service
    will that forward the traffic to this ip? and what happen if somebody wanted to connect to this ip which one will be chosen?

    thnks much

  5. #5
    Super Moderator lupin's Avatar
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    Quote Originally Posted by ann06 View Post
    umm, thanks for the clarification lets say i set this manual ip same like the one with important service
    will that forward the traffic to this ip?
    You'll get unpredictable results. This is not really the way to go about intercepting traffic.

    In addition, depending on the OS of the machine running the important service, that machine will get error messages that a duplicate IP address exists on the network - so this method can be easily detected.

    Quote Originally Posted by ann06 View Post
    and what happen if somebody wanted to connect to this ip which one will be chosen?
    Depends. On an Ethernet network IP addresses are normally mapped to a MAC address based on the response to an ARP resolution request. When one machine wants to talk to another in the same broadcast domain (a system it doesn't have to use a router to talk to) it will send a broadcast frame asking who has the destination machine's IP address - then the machine using that address should reply. This way the sending machine can find out the hardware address it should send its communications to.

    If two machines have the same address I would imagine they would both respond to a request for their address, however this may be Operating System dependent. Operating Systems that can detect duplicate IP addresses on the network may not respond at all.

    If both machines did respond maybe the first response received is the one that is used by the requesting system. It should then cache that response for a period of time and use it for future communications. Of course its also possible that if a machine receives two responses to an ARP resolution request, it may assume that somethings wrong and the communication may fail. You'd probably need to test this to be sure, but again I wouldn't recommend you use this as a method of intercepting traffic.
    Capitalisation is important. It's the difference between "Helping your brother Jack off a horse" and "Helping your brother jack off a horse".

    The Forum Rules, Forum FAQ and the BackTrack Wiki... learn them, love them, live them.

  6. #6
    Just burned his ISO
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    Thanks for your rich information
    Regards

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