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how to find a free IP address on a network

Discussion in 'Tech Support' started by sotu1, 16 May 2008.

  1. sotu1

    sotu1 Ex-Modder

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    as the title says, does anyone know how to find an open ip address on a server based network? rather than picking one at random and hoping it's free, is there a better way to do this?

    help muchosly appreciated!
     
    sotu1, 16 May 2008
    #1
  2. notatoad

    notatoad pretty fing wonderful

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    dhcp client?
     
    notatoad, 16 May 2008
    #2
  3. badders

    badders Neuken in de Keuken

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    Advanced IP scanner will let you scan each IP in your B or C subnet (B takes a while), is threaded for multicore processors, and will tell you whether each one responds to ping or not. It'll also give you the netBIOS info for each one.
     
    badders, 16 May 2008
    #3
  4. Fod

    Fod what is the cheesecake?

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    "arp -a" in a cmd shows all ethernet adaptors your machine can see.

    works for me.
     
    Fod, 16 May 2008
    #4
  5. Gareth Halfacree

    Gareth Halfacree WIIGII! Lover of bit-tech Administrator Super Moderator Moderator

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    Checking the ARP table as per Fod's suggestion is good, but be aware that if you're running a large network with statically-assigned addresses and no management (as opposed to static assignments distributed via a DHCP server) then you're asking for trouble. If a computer is switched off, you won't realise it's got a static IP address - and when it comes back on, it'll conflict with yours if you've chosen the same one.

    I'd recommend putting a DHCP server in place - you can still give each computer a static IP address, but it means that the address will remain reserved even if the PC is off.
     
    Gareth Halfacree, 16 May 2008
    #5
  6. Phil

    Phil What's a Dremel?

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    whatever you do, don't purely rely on PING either. Once upon a time at $work, our $isp reallocated our Gateway IP address to another customer...
    we'd set it not to reply to Pings* and so when they pinged the host and got no response, falsely assumed it was a free IP address. Bad move.

    *tbh, blocking ICMP echo request on a piece of networking equipment like a router is a baaad idea.
     
    Phil, 16 May 2008
    #6
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