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I am trying to understand what data is actually stored on a DHCP server. I understand the process of how a client gets a lease for an IP address from a server, but is it possible to poll a server for the hostname of the client that has a given IP leased?

For example: I can ask the DHCP server "What is the hostname of 192.168.1.107?" and it will return "Jim's Lenovo".

From my understanding when a client attempts to ask for a lease, the DCHP Request packet can contain the hostname depending on the option set. However, does the server hold this hostname?

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  • I think you would need a DNS server for this. DNS is the thing that translate names to ip's and with a reverse lookup the other way around. Once you've set your default DNS to your server IP you could do nsloopup computername and it will give you IP. or reversed.
    – RamonRobben
    Feb 28, 2017 at 22:12
  • Thank for your answer! However, I am already aware of the DNS solution, I was wondering if it's possible with DHCP.
    – Jon
    Feb 28, 2017 at 22:21
  • ietf.org/rfc/rfc2131.txt, section 2.1: "The model of DHCP persistent storage is that the DHCP service stores a key-value entry for each client, where the key is some unique identifier...The protocol defines that the key will be (IP-subnet-number, hardware-address) unless the client explicitly supplies an identifier using the 'client identifier' option." In other words, it stores the key, and the key is what the client supplies. Case in point: "Alternately, the key might be the pair (IP-subnet-number, hostname),"
    – MaQleod
    Feb 28, 2017 at 22:25

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The DHCP server doesn't maintain a list of hostnames, but will maintain a DHCP Lease list, which would include the MAC address of the device and IP address that was assigned to it. Name resolution is something completely different.

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  • I read on Microsoft's DHCP documentation that a client can send there hostname with through an option in the DHCP REQUEST packet. Theoretically, if this were the case, would the lease list contain that information?
    – Jon
    Feb 28, 2017 at 22:26
  • It does, if you look in a Windows Server's DHCP Lease List, if the client includes it but it is not required to do so... But I don't know of anyway you could query that other than on the server.
    – acejavelin
    Feb 28, 2017 at 22:38
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    @Jon, yes, the option to set is "client identifier" as defined in the RFC (see my comment above). The process is defined more in section 3: "The combination of 'client identifier' or 'chaddr' and assigned network address constitute a unique identifier for the client's lease and are used by both the client and server to identify a lease referred to in any DHCP messages."
    – MaQleod
    Feb 28, 2017 at 22:38

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