Thanks you for this information. How does the Host name play into the dhcp
leases?
Is the IP handed out based on MAC address, or based on the Host name?
thank you
Philippe
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:e5:28 192.168.0.50 debian-host *
1177928854 00:15:e9:a8:e6:c5 192.168.0.57 carm 01:00:15:e9:a8:e6:c5
1177849379 00:03:2f:3a:f2:e9 192.168.0.54 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.
