Frustrating Mac address

Discussion in 'Wireless Internet' started by Dusty, Sep 13, 2015.

  1. Dusty

    Dusty Guest

    Whenever I run a program to check machines & IP addresses on my
    network, I notice that my tablet IP address keeps changing. I went
    into my router settings and assigned a specific IP address to each
    Mac address. The IP address still changed. Finally I noticed that
    every time the tablet reboots, it gets a new Mac address.

    Why does this happen?

    Should this be able to happen?

    I thought Mac addresses were permanent?

    I only have five devices on the network, and wanted them to
    go from to instead of jumping all
    around like the tablet getting sometimes, then another time, or any number in between.

    This is a Chinese tablet, called Dragon Touch. It's inexpensive but
    it's good, except for the Mac address problem.

    There doesn't seem to be a way to specify a permanent Mac address
    in the settings.

    Could having the Mac address keep changing be good for security?

    Curious & frustrating
    Dusty, Sep 13, 2015
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  2. The consensus and associated conspiracy theory is that it's because
    some companies are too cheap to buy sufficient MAC addresses:
    Judging from the code fragment, it seems to be intentional. Using a
    random MAC address within a small MAC address space, allows
    considerable MAC address reuse and saves the manufactory about $645
    for 4096 addresses or about $0.16/address. If you're shipping 10
    million devices, that's $1.6 million saved, so this not spare change.
    In the distant past
    That also suggests it's intentional.
    That's a minor reason compared to the cost. If you include anonymity
    and stealth as part of "security", then yes. There are numerous apps
    for PC, MAC, OS/X, and various devices for changing the MAC address.
    The idea is that it makes the device more difficult to identify. I
    guess the Dragon Touch people decided to make it a feature.

    Strictly speaking, there's nothing really wrong with random MAC
    addresses, except that filtering by MAC address won't work, the log
    files will be a mess, the ARP table on the router might overflow if
    rebooted too often, ethernet switches might complain, and various
    authentication schemes for VPN's might fail.

    Do your MAC addresses begin with 00:90:4C ??
    Jeff Liebermann, Sep 13, 2015
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  3. Dusty

    Dusty Guest

    When I did a factory reset, then reinstalled VPN One Click it wouldn't
    show that I still had ten months left on the subscription. I had to work
    with tech support quite a bit to get the problem worked out.
    They start with 00:08:22
    Thank you Jeff
    When the alien overlords take over earth, you will be protected.
    Dusty, Sep 14, 2015
  4. Dusty

    Dusty Guest

    Dusty, Sep 14, 2015
  5. There are various methods of VPN authentication. It has to be
    something on your machine that does NOT change. Usually, it's the MAC
    address, sometimes the IP address, and in desperation, a login and
    password. Yeah, I can see a problem.
    I found this work around for a different phone, but which seems to be
    usable, if your tablet is rooted. You get to pick your own MAC
    address, which has its limitations and dangers. The MAC address does
    NOT go through the router to the internet and is used only on your
    LAN. The only exceptions I can think of is the VPN authentication
    problems. With a limited number of machines on your LAN, chances of a
    duplicate MAC address is minimal.
    Jeff Liebermann, Sep 14, 2015
  6. Dusty

    Dusty Guest

    There seem to be a jillion ideas on how to root a tablet, which,
    so far, haven't worked on this one.
    Dusty, Sep 16, 2015
  7. With only having 5 devices on a network and only 1 of them doing what
    you describe, with the proper router you could still control it.

    Set your DHCP limit to only assign 5 possible address values, 2-6.
    Then assign every machine a "fixed" address except the problem device
    using the routers ability to lock an IP address to a specific MAC
    address. Reboot all devices so the new address values get assigned to
    each of the non-problem devices by the router. The problem tablet
    should now be forced to take the last available DHCP address every time
    as the others would already be "busy" according to the router.
    GlowingBlueMist, Sep 16, 2015
  8. Dusty

    Dusty Guest

    That is a good idea.
    Dusty, Sep 17, 2015
  9. Dusty

    Char Jackson Guest

    That's a creative solution, but it looks like there could be a potential
    issue with the tablet.

    Turn the tablet on and it gets its one and only available IP address via
    DHCP. The other 5 addresses are reserved, so it gets what's left. Per the
    router, the DHCP lease is good for X mins/hrs/days. Now, partway through the
    lease period, the tablet is turned off, then sometime later but still within
    the original lease period it's turned on again. It'll request an IP via DHCP
    but now there are no DHCP addresses available. You have to wait for the
    existing lease to time out and expire.

    I suppose a workaround would be to set a very short DHCP lease period, with
    the knowledge that doing so will affect all 6 of the OP's network devices,
    since the lease setting is global. What would be a good lease duration? 10
    minutes, so everything renews every 5 minutes? Just thinking out loud. For
    me, my DHCP lease period is currently 24 hours, but I've seen NAT routers
    that default to 7 days. Such a long period clearly wouldn't work for the OP
    and his crazy tablet.
    Char Jackson, Sep 17, 2015
  10. Dusty

    Dusty Guest

    There doesn't seem to be a way to set DHCP lease time on this router.
    It shows when the lease began, and when it ends.

    I've enclosed a link for the router Manuel if you want to see if you can
    find a way, if I missed it.

    The other routers can change lease time, but the way the network is
    set up, this router needs to cover the center of the house, while the
    others cover the ends, unless I wire in a switch, then use the WAP in
    the middle and put this router at the end, but the WAP is old and tends
    to overheat so I only plug it in when needed. If I get another WAP it
    will be an outdoor one for long range.

    I wonder if the long range WAP will cover the whole house if I put it at the
    end, about 6ft above the roof?
    Dusty, Sep 19, 2015
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