Long 44 character mac address?
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  1. #1
    Join Date
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    Linux (Fedora) Chrome 68.0.3440.106

    Long 44 character mac address?

    Fedora 28
    # uname -a
    Linux openvpn_lrri_tunnel.mind.unm.edu 4.17.19-200.fc28.x86_64 #1 SMP Fri Aug 24 15:47:41 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux

    This is the weirdest thing I have seen.

    So itself, other fedora and ubuntu machines see it as a 6 character mac in arp
    In windows dhcp server when I add it to reservations it shows up as 44 characters.

    I am running fedora in a vm. I thought maybe changing the adaptor type would make a difference but it did not.
    I tried VMXNET 3(default), E1000, E1000E, and VMNET 2 (Enhanced).
    All four showed as 44 character mac addresses when I added then to my dhcp server.
    I just checked my non vmware machine and it too has the same behavior with windows dhcp server.

    My ubuntu vm's only show up as 6 character mac addresses when I add them to my windows dhcp server

    Machine in question
    on istelf

    [root@openvpn_lrri_tunnel ~]# ip addr show ens192
    2: ens192: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
    link/ether 00:50:56:9e:63:0f brd ff:ff:ff:ff:ff:ff
    inet 10.0.100.253/22 brd 10.0.103.255 scope global dynamic noprefixroute ens192
    valid_lft 26195sec preferred_lft 26195sec
    inet6 fe80::b8b0:7b2a:ac15:60bf/64 scope link noprefixroute
    valid_lft forever preferred_lft forever

    Windows dhcp server reservation MAC address:
    569e630f000439045c7fd3624c54b4633ba604c32e04

    What is going on with Fedora networking?

  2. #2
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    Linux (Fedora) Firefox 62.0

    Re: Long 44 character mac address?

    It's not Fedora that's doing something odd, it's Windows.
    It took the last 8 chars of your ens192 I/F MAC, stripped the colons and made a new string-> 56:9e:63:0f -> 569e630f and made that the first 8 chars of the 44 char MAC id

    569e630f000439045c7fd3624c54b4633ba604c32e04

    The last 32 char part: 000439045c7fd3624c54b4633ba604c32e04 I suspect is some kind of random identifier that Windows generates. The RFC for dhcp says:

    The 'client identifier' is an opaque key, not to be interpreted by the server; for example,
    the 'client identifier' may contain a hardware address, identical to
    the contents of the 'chaddr' field, or it may contain another type of
    identifier, such as a DNS name. "

    so the RFC doesn't require that the id be the actual MAC, it's just that most implementations do that because it's just so obvious (MACs are worldwide guaranteed unique (assuming the company making the equipment did it right, using their allocated company prefix and so on)). My guess is that the final 32 chars is just some kind of encoded string that contains information about the host. I found a post

    https://social.technet.microsoft.com...or-dhcp-client

    where a guy did a hex to ascii conversion of his string and it was "DELL4WBOM02" and the guy stated his hosts were in fact Dells. I also notice that 32 chars is the length of a md5sum hash:

    echo -n "blahblah" | md5sum -
    42d388f8b1db997faaf7dab487f11290 -

    echo -n "42d388f8b1db997faaf7dab487f11290" | wc -c
    32

    so it's possible windows has some kind of identifier it wants to use but also obscure it so it md5sum's it and uses that
    Last edited by marko; 16th September 2018 at 12:46 AM.

  3. #3
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    Linux Chrome 68.0.3440.106

    Re: Long 44 character mac address?

    Ok, then why does it only do this with Fedora 28? Why does it not see Ubuntu 18.04 this way? No, something is different about dhclient or what ever fedora 28 is using that is causing the dhcp server to see it that way.

  4. #4
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    Windows 7 Firefox 61.0

    Re: Long 44 character mac address?

    I observed this behavior on my Windows 2008R2 dhcp server for Fedora 22 clients as well, so it must not be new to Fedora 28. I remember having a hard time reserving IP addresses for my Linux systems because their MACs as recorded by Windows could differ, and be really long, have this weird hash in it.

  5. #5
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    Linux (Fedora) Chrome 68.0.3440.106

    Re: Long 44 character mac address?

    Quote Originally Posted by bgstack15
    I observed this behavior on my Windows 2008R2 dhcp server for Fedora 22 clients as well, so it must not be new to Fedora 28. I remember having a hard time reserving IP addresses for my Linux systems because their MACs as recorded by Windows could differ, and be really long, have this weird hash in it.
    Thank you. I will eventually file a bug report. I don't think it effects anything but windows dhcp servers. I have no issues with my isc dhcp server nor do I have any issues with anything else seeing the mac address wrong. Almost certain it is some response in dhclient. Even my windows dhcp server sees the mac address correctly in the arp table.

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