I have 2 wireless cards with the same MAC address at the hotel

Discussion in 'Wireless Networking' started by Jette Goldie, Sep 30, 2006.

  1. Jette Goldie

    Jette Goldie Guest

    I have two working PCs with the same MAC address!
    How do the packets figure out which computer to go to?

    I have been travelling with two computers for weeks now staying at some
    German hotels whose wireless ISP sync with the MAC address of the wireless
    cards on my computers so I used MacMakeUp to make both computers have the
    same MAC address as I get my home email on my home PC and I get my work
    email on my work PC. Up until today, I was careful to boot only one
    computer at a time.

    I'm currently in a hotel in the UK which has free wireless to any MAC
    address and I forgot to reset the MAC address on the second PC back to the
    original. Both computers seem to be working wirelessly.

    How can that be?

    How can I have two working PCs with the same MAC address?
    Why don't the packets get confused as to which computer to go to?

    Jette Goldie, Sep 30, 2006
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  2. Jette Goldie

    FedUp Guest

    Because the packets are not routed to a mac address they are route to an IP
    FedUp, Sep 30, 2006
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  3. Jette Goldie

    Pavel A. Guest

    Are they connected to same access point?

    Pavel A., Sep 30, 2006
  4. Jette Goldie

    Duane Arnold Guest

    It's because a NAT device such as a router is being used. The router has a
    DHCP server that issues an unique IP to each NIC requesting that an DHCP IP
    be issued to it. NAT is mapping technology it maps traffic back to the
    requesting IP/machine's NIC that sent outbound traffic to a remote IP on the
    Internet. Not only does the router apply the MAC in the network traffic when
    it sends traffic outbound, it also applies the LAN IP that has been assigned
    to the NIC too in the traffic, so that the inbound traffic can be mapped
    back to the requesting machine. Inbound traffic is not mapped back to a
    machine, unless there is corresponding traffic sent outbound by the machine,
    which has a LAN IP.

    Duane :)
    Duane Arnold, Sep 30, 2006
  5. Jette Goldie

    Baloo Guest

    If you assigned the MAC on one, and left the other in it's original form,
    the MAC's are actually one bit apart: The last bit indicates that the MAC
    was set and not the factory MAC address.
    Baloo, Sep 30, 2006
  6. Jette Goldie

    Baloo Guest

    At the network level, maybe, but not at the data link level. You might want
    to read up on the OSI 7 Layer Model before making such statements.
    Baloo, Sep 30, 2006
  7. Jette Goldie

    AJR Guest

    Does not compute! MAC is a hardware address "permanently burned-in" by the
    manufacturer. If Windows detects two identical MACS a system event log
    entry is generated and network connectivity cease.

    Following also quoted from Knowledge Database Article ID 164903: "Another
    source of duplicate media access control addresses can occur if you are
    assigning locally administered media access control addresses (LAA), in
    which case you are overriding the burned-in address in favor of the locally
    assigned media access control address. With some drivers, LAA media access
    control addresses are possible, usually Token Ring adapter drivers."
    AJR, Sep 30, 2006
  8. Jette Goldie

    Eric Guest

    Keyword: "seem"

    Run Ethereal or some SNMP utility and you'll probably find quite a bit of
    collisions going on...
    Eric, Sep 30, 2006
  9. Jette Goldie

    FedUp Guest

    You are correct. I jumped the gun and answered before fully understanding
    the OP situation. My apologies to the OP. Disregard my comment.
    FedUp, Sep 30, 2006
  10. Jette Goldie

    Baloo Guest

    Please quote in the same manner we all read English: Conversational order.
    Please see http://ursine.ca/Top_Posting
    Not necessarily. Some devices, such as some high end network cards and SOHO
    routers, have the ability to set the MAC address. One of the MAC address
    bits, IIRC, indicates whether the MAC was set by human intervention or the
    one it shipped with.
    Baloo, Sep 30, 2006
  11. Jette Goldie

    Eric Guest

    Drive-by replying?

    Read his post again...

    ("so I used MacMakeUp to make both computers have the same MAC address")

    That computes how he could have two NIC's with the same MAC.
    Eric, Sep 30, 2006
  12. Jette Goldie

    Jette Goldie Guest

    They are within five feet of each other so I presume they connected to the
    same free wireless access point in the hotel.
    Jette Goldie, Oct 1, 2006
  13. Jette Goldie

    Jette Goldie Guest

    Hi Nat,
    Does this mean that each computer gets TWO unique addresses?
    The MAC and the IP.

    Are you saying that even though the MAC address is the same, that the
    combination of Mac + IP address is different because the IP addresses are
    Jette Goldie, Oct 1, 2006
  14. Jette Goldie

    Baloo Guest

    Many wireless networks can occupy the same airspace. You need to
    doublecheck your connection properties to make sure they really are on the
    access point you expect to be on.
    Baloo, Oct 1, 2006
  15. Jette Goldie

    Jette Goldie Guest

    Oh, Do you mean the same SSID?
    I had not thought of the fact they 'could' be connected to different SSIDs.
    But, in this case, the SSID is definately the same for both Windows XP PCs
    as it's the only free SSID available.

    I'm checking out at noon today (on my way to South Africa) so I won't be
    able to respond for a while.

    Jette Goldie
    Jette Goldie, Oct 1, 2006
  16. Jette Goldie

    Jette Goldie Guest

    Is the MAC address "really" burned in?
    MacMakeUp seems to "change" the MAC address at will.

    I just checked the WinXP System Event Log by right clicking on "My
    Computer" and selecting "Manage" and then selecting "System Tools", "Event
    Viewer", "System".

    I am not sure what to look for, but, I did see......
    The system detected that network adapter
    \DEVICE\TCPIP_{BAACBE02-D4AF-43D0-BF89-D45C0B039834} was connected to the
    network, and has initiated normal operation over the network adapter.

    And ...
    Your computer was not able to renew its address from the network (from the
    DHCP Server) for the Network Card with network address D45C0B039834. The
    following error occurred:
    The semaphore timeout period has expired. . Your computer will continue to
    try and obtain an address on its own from the network address (DHCP)

    This may or may not be a red herring because the sysytem "seems" to be
    working well.

    Jette Goldie, Oct 1, 2006
  17. Jette Goldie

    Jette Goldie Guest

    The "MacMakeUp" freeware program will change the MAC address for any
    Windows PC network card.

    Can you tell from their web site whether the "human intervention" switch is
    also reset?


    Jette Goldie, Oct 1, 2006
  18. Jette Goldie

    Baloo Guest

    No, there is no way to force the clone bit off without using the original
    MAC address programmed in that NIC's ROM. The clone bit only usually comes
    into play for identification is on routers and wifi points smart enough to
    know about the bit, in the case that two devices on the network appear to
    have the same MAC, and even then it's not foolproof if more than one device
    is cloned on the same network.

    Some cable and DSL providers have been known to not allow devices that have
    the clone bit set to talk to the cable modem or DSL bridge/router, but
    that's a fairly rare case.
    Baloo, Oct 1, 2006
  19. Jette Goldie

    Baloo Guest

    Yes, there's usually some method to revert a programmable network device
    back to it's original MAC.
    You have a programmable network card and are telling it to spoof a different
    MAC address.
    I don't know enough about Windows error messages to know what it's calling a
    semaphore timeout (though I wouldn't mind learning). Only thing I can
    think of is that your machine sent a DHCP request, the DHCP server
    responded with an answer and the other machine with the same MAC address
    answered first, the first machine then ignores the acknowledgement it
    wasn't expecting to get out of order and times out, however, this is just a
    theory I can't prove without a packet analyzer on the same network you're
    on. I don't have a lot of confidence in my hypothesis though: Most people
    make it a point not to put two of the same MAC address on the same network.
    Baloo, Oct 1, 2006
  20. Jette Goldie

    David Hettel Guest

    More than one access point can have the same SSID, and to enable seamless
    roaming this is necessary. What you would want is to compare the Associated
    MAC address or BSSID of the connected access points.

    David Hettel

    Please post any reply as a follow-up message in the news group
    for everyone to see. I'm sorry, but I don't answer questions
    addressed directly to me in E-mail or news groups.

    Microsoft Most Valuable Professional Program

    DISCLAIMER: This posting is provided "AS IS" with no warranties, and
    confers no rights
    David Hettel, Oct 1, 2006
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