[Dnsmasq-discuss] dnsmasq.lease file question

Philippe Faure philippe at faure.ca
Thu May 10 13:06:51 BST 2007

Thanks you for this information.  How does the Host name play into the dhcp

Is the IP handed out based on MAC address, or based on the Host name?

thank you


> Mr Gabriel wrote:
>> I too have noticed this strange phenomena, and not just in DNSMasq. On
>> almost every DHCP server I have ever used, when I look at the lease
>> file, there is never hardware info for linux boxes. Personally, and my
>> understanding of the underlying mechanics of DHCP is very limited, I
>> thought that all requests for a DHCP address included the mac address,
>> in order for an answer to be directed to the correct machine. Therefore,
>> the DHCP server should already know the hardware address. Why it
>> forgets, and it never gets listed, is beyond me. Maybe someone else
>> could enlighten us :)
>> On Tue, 2007-04-24 at 12:46 -0400, Philippe Faure wrote:
>>> Hello,
>>> I am running Dnsmasq version 2.2 on a Debian server version 3.1. The
>>> Dnsmasq.lease file has the following information stored in it.
>>> 1177812457 00:15:e9:a8:e5:28 debian-host *
>>> 1177928854 00:15:e9:a8:e6:c5 carm 01:00:15:e9:a8:e6:c5
>>> 1177849379 00:03:2f:3a:f2:e9 phil 01:00:03:2f:3a:f2:e9
>>> Why is it that the two windows' boxes have the hardware ID there, while the
>>> linux (Ubuntu Feisty, running dhcpcd) only has a *?
>>> Is there some setup that I have done properly? if so with the 
>>> client or server?
>>> Do I need to worry about it?
> This is a tale of two different identifiers: the MAC address and the 
> client identifier. The final item on each line in the leases file is 
> a client identifier.
> Client identifiers are optional: if one is not provided then the DHCP 
> server just uses the MAC address to track the host, but if a 
> client-id is present, it trumps the MAC address. This has interesting 
> applications: if a machine uses a serial number as its client-id, 
> then replacement of a network interface (changing the MAC address) 
> won't interfere with a DHCP lease.
> In practice, unless specially configured, common clients either don't 
> send a client-id, or send one derived from the MAC address, so the 
> presence or absence really doesn't matter.  In this case, windows 
> sends a client-id but dhclient doesn't. It's not a practical problem 
> either way round, and nothing to worry about.
> Interestingly, it's possible to have a client-id and no MAC address. 
> Firewire does this, because firewire MAC addresses are larger than 
> the MAC address field in a DHCP packet.
> Cheers,
> Simon.

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