[Dnsmasq-discuss] Always Ignore Client Identifier

Linux Luser linuxluser at gmail.com
Wed Jan 29 18:04:41 GMT 2014

We have a pretty tightly-controlled private network environment which we've
configured to have a 1-to-1-to-1 relationship between client MAC address,
hostnames and IP addresses. Apart from "guest" IP ranges, we have control
over when clients get added to the network. Thus, we can detect duplicate
MAC addresses before it becomes an issue.

In this setup, we can't need or want to use the "client identifier" option
of DHCP. In fact, it becomes a problem when we start doing PXELinux
installs, where a different client id gets sets during a remote install
session, then when the install is complete and the new OS boots up, it gets
a different IP address (because dnsmasq still knows about the lease it gave
that same machine only 10 minutes ago!).

To get rid of this issue, we now supply a dhcp-host option to dnsmasq each
time we want to do a remote reinstall. The option looks something like this:
dhcp-host=<MAC addr>,id:*,<hostname>,<IP addr>,set:install

This works, since the "id:*" part tells dnsmasq to ignore the client ID in
favor of the MAC address. But now to my question. Can this be done for ALL
DHCP requests? Is there a global "identify-by-mac-only" option? If not,
would you be willing to entertain the idea. I know many others have done
this for some time now, using other DHCP server software, so I know it's
possible and there doesn't seem to be any ill effects of this.

Maybe this is not a good idea? Like I said, we have a fairly controlled
environment, so it would work for us. I could see how this would be
unnecessary for common setups, though. Or environments that have many VMs
running on a single host and simply bridge their network interface may want
to use the "client identifier" option so each VM gets a unique IP even if
they're running on the same machine. But it would be nice to have a greater
level of control over this.

Thanks for your time. And GREAT piece of software, by the way. dnsmasq is a
HUGE time saver and makes changing configurations straight-forward. Do you
accept donations? :)

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