[Dnsmasq-discuss] Always Ignore Client Identifier
Simon Kelley
simon at thekelleys.org.uk
Fri Jan 31 21:48:17 GMT 2014
On 31/01/14 16:25, Linux Luser wrote:
> dhcp-ignore-names is concerned about the hostname, correct? I am
> interested in the client identifier option sent in the DHCPREQUEST.
> Ignoring this field would break RCF2131 (and probably some people's
> networks!) but in my particular case, it may spare me some problems.
I understand, I'm proposing a new option, dhcp-ignore-clid, analogous to
the existing dhcp-ignore-names.
>
> Maybe if I could selectively revoke leases, that would work. Could I do
> this? I'm sure that dnsmasq keeps an internal cache, so that would have
> to be flushed for a particular lease.
There is a utility in contrib/wrt in the source distribution, and a
binary in the Debiann package of dnsmasq, for releasing a specific lease
from the command-line.
>
> On Jan 30, 2014 2:08 AM, "Simon Kelley" <simon at thekelleys.org.uk
> <mailto:simon at thekelleys.org.uk>> wrote:
>
> On 29/01/14 18:04, Linux Luser wrote:
>
> 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.#
>
>
> There isn't a global option to do this, but there is precedent, in
> the form of --dhcp-ignore-names for adding it, and actually that's
> something more useful, since the tag system allows the setting to be
> applied to classes of clients (which could, of course, be "all clients")
>
>
> 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 or t 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? :)
>
>
> Donations by Paypal to simon at thekelleys.org.uk
> <mailto:simon at thekelleys.org.uk> are always welcome, or you could
> commission me to add new features. I'm available for that on a
> consultancy basis, cheaper for stuff which goes back into the
> dnsmasq GPL codebase, more expensive for proprietary code.
>
>
>
> Cheers,
>
> Simon.
>
>
>
> --
> daV.e
>
>
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