Can two different computers have the same IP address?

Discussion in 'Computer Support' started by Clueless in Seattle, Aug 21, 2007.

  1. A while back I joined an old-fashioned computer BBS for old times'
    sake (back in my CP/M days, before the advent of the web, BBSs were
    all we had. So upon learning that there was an active BBS that I
    could telnet into I thought it would be fun).

    Well, it has been anything but fun.

    Almost as soon as I started posting messages I started getting
    viciously flamed by a fellow who is claiming that my IP address is
    identical to the IP address belonging to someone else who posts to
    the board. Apparently these two gusy have a long standing feud and
    now I'm being accused by one of them of being his old nemesis logging
    in under a different name.

    I don't understand anything about IP addresses and how they are
    assigned, but I thought that they were supposed to be unique

    So is it even remotely possible that somehow my computer and another
    computer miles away from me could both have the same IP address?

    Will in Seattle
    a.k.a. "Clueless"

    P.S. I know! The simplest and easiest solution to this problem would
    be to just abandon the BBS and never log in there again. I mean, why
    would I want to log into a BBS where I'm the target of rude and
    abusive postings, right? But, this fellow's claim that may computer
    shares an IP address with another computer not connected to mine in
    any way that I can conceive of has piqued my curiosity, so I'm
    wondering if such a thing could even be possible, no matter how
    Clueless in Seattle, Aug 21, 2007
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  2. Clueless in Seattle

    Mike Easter Guest

    All things considered, fundamentally the most likely thing is that
    either your flamer is confused or that someone else accessed by the same
    dialup modem access provider as you. See below.
    If you access the telnet via a dialup connectivity provider's modem, you
    could access with the same IP as someone else who used that dialup. See

    If you had a home local network, you could have the same IP as someone
    else on your network.

    You are connecting to GG via a free dialup provider which has 36 telnos in 5 area codes in western
    WA and which your current connectivity indicates the netblock provider
    to be US Network Services
    Not your computer. When you dialup on your telephone modem you reach a
    connectivity provider which is the IP the google webserver sees and
    which is the IP the telnet BBS sees. That could be the same
    connectivity that someone else uses.
    Mike Easter, Aug 21, 2007
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  3. Most people show an IP address based on what their internet provider
    "hands out" to them, taken from a pool of addresses available to the
    ISP. You seem to be using a service called and posting from
    the Seattle area. This may be way off. But it's entirely possible that
    you have assigned to you temporarily a number that was used by someone
    else to post. But since you mention "improbable", the probability of you
    getting the same number as some old antagonist as your IP assignment and
    then you logging into the same BBS under that number and being spotted
    would be astronomical in my opinion. It would seem more likely you are
    lying to us right now and are simply trying to be someone you're not to
    some git you're having an argument with.
    =?ISO-8859-1?Q?R=F4g=EAr?=, Aug 21, 2007
  4. Clueless in Seattle

    Whiskers Guest


    The short answer is 'yes, but not at the same time'.

    The IP number you're talking about is the 'internet address' of your
    internet connection. If your ISP provides you with a 'dynamic IP', you
    may well get a different IP number each time you log on to the internet -
    and meanwhile, other customers of your ISP may be allocated the number you
    previously had.

    In the longer term, whether you have a dynamic IP or not, when you change
    ISP you will get a new IP number, from one of the 'blocks' 'owned' by the
    new ISP, and someone else will get the IP number you had from your old

    If an ISP gives up some of the blocks of IP numbers it was allocated, or
    if it stops trading completely, then those numbers will be available for
    other businesses, including other ISPs.

    So you could indeed 'inherit' an IP number from someone else who had it
    before, and two customers of the same ISP might easily find themselves
    sometimes getting an IP number recently used by the other.

    If your ISP is a 'reseller' of internet services provided by a wholesaler,
    you may find that the block of IP numbers from which you get yours, is
    shared by more than one 'reseller' ISP.

    IP number alone is not sufficient to identify 'the same person', all it
    does is indicate a possibility.
    Whiskers, Aug 21, 2007
  5. Clueless in Seattle

    Leythos Guest

    Most IP addresses, Public Ones, are provided to ISP's in blocks. Those
    blocks are allocated by the ISP as needed, some a re static ranges, some
    are dynamic. If you share the same ISP as anyone else, given enough
    time, based on the number of IP they have available you could easily get
    the same IP (at a different time) as anyone else on the ISP's same

    This was very common on Dial-Up networks, where the ISP's had 1 IP for
    every 10-30 users that subscribed.

    Today, with IP's even more in demand all over the world, if you leave
    your computer disconnected for (normally 12 hours to 7 days), depending
    on the ISP's lease settings (normally 1 day), you will get a different
    IP than you had the period before.

    If you and the person in question are using different ISP's then it's
    very unlikely that you have the same IP as the person once had.

    Leythos - (remove 999 to email me)

    Fight exposing kids to porn, complain about sites like PCBUTTS1.COM that
    create filth and put it on the web for any kid to see: Just take a look
    at some of the FILTH he's created and put on his website: all exposed
    to children (the link I've include does not directly display his filth).
    You can find the same information by googling for 'PCBUTTS1' and
    'exposed to kids'.
    Leythos, Aug 21, 2007
  6. Up to now I'd always found this newsgroup to be an island of civility
    and helpfulness in an electronic sea increasingly polluted by the
    excrement of boorish louts.

    I guess the lesson to be learned here is that if you drop your hook
    into the sea often enough, odds are that one of these days you'll
    eventually snag a turd instead of a catching a fish.
    Clueless in Seattle, Aug 21, 2007
  7. Yes, that's true. And if you try to pretend to be someone you're not and
    get caught with your pants down, well, there you are with your pants
    down. You want/expect others to believe in the outlandishly
    impossibility that you logged in to your ISP, got the same dynamic IP
    address as someone embroiled in an argument, and then logged into the
    same BBS that they frequent? I'd say your pants are down.
    =?ISO-8859-1?Q?R=F4g=EAr?=, Aug 21, 2007
  8. OK, so it's not my computer, but my ISP that is identified by the IP
    address, right?

    So, then, if I understand what you've told me, it is possible for
    this other fellow to have posted messages to the BBS , and have them
    tagged with the same IP address.

    Here's why:

    The other guy lives in my same area code, so he could have used to dial-up and telnet in to the BBS. I don't think
    that's very likely, because I know that he uses I high speed
    connection that he gets from the phone company or his cable provider,
    I forget which. But, it is possible, that for some reason, he
    decided to use to connect to the BBS.

    I just emailed him to find out if he's ever used, but
    don't have an answer yet. So, let's just assume for the moment that
    he did use That would greatly reduce the odds against
    his having the same ISP as me, right?

    But, given that has about 15 or 20 different dial-up
    phone numbers in the Seattle area, what are the odds that he would end
    up with the same IP address everytime he connects to the BBS? And the
    same for me, what are the odds that I would end up with the same IP
    every time I called the BBS. And then, what would be the odds that
    the two of us would have the same IP address everytime either of us
    called the BBS. It would still be pretty slims odds, wouldn't it?

    But still, within the realm of the possible? Sort of like the odds
    that would pick the right Lotto numbers or something?
    Clueless in Seattle, Aug 21, 2007
  9. Clueless in Seattle

    Mike Easter Guest

    Not exactly. The issue is the 'connectivity' provider. It is very very
    common for some ISP to 'buy' the connectivity for their subscribers from
    someone else. For example, EarthLink buys its cable modem connectivity
    in my area from TimeWarnerCable, which is also the entity that provides
    cable connectivity to RoadRunner and AOL. EL also buys its dialup
    connectivity from level3, which level3 sells dialup connectivity to
    others besides EL.

    In your case, it appears that your ISP may not be buying
    telephone connectivity from other providers in the same way that EL buys
    its connectivity from other providers -- but I don't know for sure. The
    netblock for your IP belongs to US Network Services but it resolves to
    nocharge. It isn't always easy to tell who has a deal with who to
    provide what.
    It is possible, but that seems to me to be an unlikely coincidence. If
    you were dialing a local BBS in the old fashioned telephone way, then
    everyone who is accessig the BBS is likely to be from the same
    geographic area to save telco toll charges, in the old days. But now
    that BBSes are telnet, then the participants come from all over the
    world -- so the likelihood that two different telnetters to the BBS
    dialed up the same access connectivity is thin. But it is possible,
    especially if your flamer 'exaggerated' and simply mean that your IP was
    in the same netblock as someone else's IP at some other time.
    Well then, if he's in the same area code, that changes the odds all over
    the place.
    If he's going to be a troublemaker, he gets a lot of anonymity by using
    a free dialup. He doesn't have to disclose any meatspace identity when
    he uses a free service, because he doesn't have to pay with anything --
    and when he uses a dialup he's not using a connectivity provider which
    can be 'attached' to him like his own broadband provider.
    If he used the same area code nocharge dialup as you, that would make
    his IP address either the same or likely almost the same.
    Most people use the same dialup telno; and when I looked, nocharge only
    showed me 4 telnos in Seattle.
    What you are now describing is more likely than not; much much more
    than 'possible'.
    Mike Easter, Aug 21, 2007
  10. Clueless in Seattle

    lee houston Guest

    You're right on the dialup, Mike. Also, many broadband
    users get their IP via DHCP and it can change upon
    power cycling the modem. Or doing a release/renew
    IP. so the same IP could be assigned, at one time or
    another, to many different users of a broadband

    lee houston, Aug 21, 2007
  11. Aha!

    Many thanks for taking the time to help me understand this!

    Will in Seattle
    a.k.a. "Clueless"
    Clueless in Seattle, Aug 22, 2007
  12. Thanks to all of you who contributed replies.

    I will post a complaint, asking that the flamer be moderated. But
    after that I don't think I'll bother visiting that BBS again. It
    seems to be populated by twenty something goth types who get their
    kicks trashing newbies.

    I'm nearly 65 and from what I gather from one of the above replies,
    there are still lots of BBSs out there, so I think my time would be
    better spent looking for one where folks civil.

    I'll see what Google can turn up.

    Again, thanks to all of you,

    Will in Seattle
    a.k.a. "Clueless"
    Clueless in Seattle, Aug 22, 2007
  13. Clueless in Seattle

    Mike Easter Guest

    If you search on telnet bbs and then use the telnet bbs guide, you will
    find that there are hundreds and hundreds -- and plenty of links to the
    software which you apparently already have.

    Then once you start following those links around, you'll find more that
    aren't in the first list.

    Or, if you really get fired up about it, you can setup your own.
    Mike Easter, Aug 22, 2007
  14. Clueless in Seattle

    Grada Guest

    The IP address the BBS is "seeing" would most likely not be yours, but
    either your internet IP address which is assign to your by your ISP
    (internet service provider), or more likely, the IP address of your
    ISP's proxy server. And in answer to your question regarding IP
    address's - No two computers on the same network can have the same IP
    address and expect to work correctly. The IP address is a way of
    UNIQUELY identifying each "thing" on a network, whether it be server,
    desktop, printer, whatever. If two devices had the same IP address, then
    any communications directed to that IP address would be "fought over" by
    the two devices - and the most likely result being that each receives
    only part of the messages. Hope this helps.
    Grada, Aug 24, 2007
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