[Dnsmasq-discuss] Always Ignore Client Identifier

Simon Kelley simon at thekelleys.org.uk
Tue Feb 11 13:36:24 GMT 2014

On 08/02/14 17:42, Linux Luser wrote:
> dhcp-ignore-clid might just work for the long-term. But I ended up
> playing around a bit more and I've managed to isolate the part of my
> config that I believe triggers the problem. Maybe this can be fixed
> without a dhcp-ignore-clid option?
> When I set a host's MAC address and IP association in /etc/ethers (with
> the read-ethers option on of course) and that same host's IP address to
> hostname association in /etc/hosts, I am able to get a consistent IP,
> whether or not that same host is using PXE boot, the Debian installer
> (where it send the vendor-id as "d-i", which shouldn't matter in this
> case) or boots to its own image on the drive. It is consistent, that is,
> until I implement a "trick" that I wanted to use so I could whitelist
> hosts for PXEboot. That's when it got inconsistent and I would end up
> with a brand new IP address for PXE and usually another brand new one
> when the host boot into it's own OS. I could only get the IP that I had
> set in /etc/ethers if I restarted dnsmasq on the server. Otherwise the
> host would receive the same WRONG IP over and over for each renewal.
> Here's the config I had BEFORE implementing a "PXEboot whitelist":
> domain-needed
> bogus-priv
> log-dhcp
> domain=mydomain
> local=/mydomain/
> server=
> server=
> interface=eth0
> except-interface=eth1
> expand-hosts
> read-ethers
> dhcp-range=tag:known,set:controller,,,2h
> dhcp-range=tag:known,set:device,,,2h
> dhcp-option=option:router,
> enable-tftp
> tftp-root=/tftpboot
> dhcp-boot=pxelinux.0
> Now, I'll add the lines which allow me to use a directory of files for
> dhcp-host commands:
> dhcp-vendorclass=pxe,PXEClient
> dhcp-ignore=tag:pxe,tag:!install
> dhcp-hostsfile=/etc/dnsmasq-hosts.d
> Inside of /etc/dnsmasq-hosts.d then I can put files that contain lines
> like this one:
> 01:02:03:04:05:06,set:install
> ... and send a SIGHUP to dnsmasq process. After this, the host with that
> MAC address gets the tag "install" and instead of ignoring PXEboot,
> dnsmasq will respond for that host. Wonderful! Problem: now I'm getting
> wildly different MAC addresses. It's like dnsmasq is reading the files
> in /etc/dnsmasq-hosts.d and ignoring the /etc/ethers file. Is this
> expected behavior? A bug? I know that specifying a DIRECTORY instead of
> a file for the dhcp-hostsfile is kind of a new feature. (For my
> purposes, I'd prefer a directory because it's possible that several
> processes might want to write files at the same time. It's easy to avoid
> concurrency problems by putting files with unique names in a directory
> (named after MAC or hostname or UUIDs, etc).)

My guess is that dnsmasq is failing to integrate the information from 
/etc/ethers and the dnsmasq-host.d file into a single coherent record. 
There are various heuristics in the code to do that for common 
situations, but since there no real "primary key", it difficult to do it 
generally. Do you merge the settings for a MAC address. for and IP 
address, for a hostname?

The simplest solution is probably to abandon /etc/ethers, and put all 
the information in one place in the files in /etc/dnsmasq-hosts.d  It;s 
fine to keep what you have and add IP addresses and/or hostnames to that.




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