Strange Unique ID for DHCP client

Question

_{Wednesday, February 17, 2016 1:14 PM}

I've got a client in one of my scopes that I can't figure out.  Instead of a MAC address, the unique ID is a 32 character string.  I converted hex to ASCII and it translates to DELLW4€BÂÀOM02.  We use Dell workstations, exclusively.  How do I go about figuring out what this guy is and why it's not showing a MAC as it's unique ID?

Thanks

All replies (6)

_{Thursday, February 18, 2016 5:48 AM ✅Answered}

Hi heyguys,

*       >> why it's not showing a MAC as it's unique ID?*

*      * Typically, this problem occurs after  reconciling.

      The DHCP Server service stores detailed and summary IP address information in the DHCP database. When reconciling scopes, the detailed and summary entries are compared to find inconsistencies. After you select and reconcile scope inconsistencies, the DHCP Server service either restores those IP addresses to the original owner or creates a temporary reservation for those addresses. These reservations are valid for the lease time assigned to the scope. When the lease time expires, the addresses are recovered for future use.

      So, after reconciling there would be new lease appeared and may be not in use currently. You may shorten the lease duration and check to see if these lease will disappear when lease duration expired.

  Best Regards,

Cartman

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_{Wednesday, February 17, 2016 1:48 PM}

Actually, value of client ID option can be anything - DHCP protocol does not require client to use MAC as client ID, and DHCP servers should not make any assumptions about contents of client id field. The only requirement is that the supplied client ID must be unique within subnet.

Quote  from dhcp rfc:

" 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. "

It is a common practice to use MAC as a client ID, but some drivers use combinations of device tag and some unique ID, for example serial number.

Gleb.

_{Wednesday, February 17, 2016 2:05 PM}

I understand that the unique ID doesn't have to be a MAC address.  I was wondering how I could go about identifying\locating this guy on my network.  However, I think it just occurred to me what I need to do.  I was looking at the mac address tables on my cisco switches and had no MAC to go by.  I realized I should probably do show arp to try and tie the IP address to a MAC.  Doh.  

_{Wednesday, February 17, 2016 2:12 PM}

yes, once the lease is obtained, you can contact the client by IP address. You can also turn on logging of dhcp requests: ciaddr field of the request contains client's MAC address.

Gleb.

_{Wednesday, February 17, 2016 2:15 PM}

Cool.  I'll check into that.  I 'think' it's an ok guy, but would like to know for sure.  We have a night shift that does some less-than-kosher things...

_{Wednesday, February 17, 2016 2:17 PM}

See Analyze DHCP Server Log Files for more info.

Gleb.