[Dnsmasq-discuss] Help: my dnsmasq per-MAC config not working?

[Simon Kelley]

Paul Smith wrote:
> I have an environment with a standard PXE boot config, like this (in a
> file in /etc/dnsmasq.d):
> 
>         dhcp-authoritative
>         dhcp-lease-max=255
>         dhcp-boot=/tftpboot/linux-install/pxelinux.0
>         
>         # ----- Configure the FABRIC network
>         dhcp-range=FABRIC,10.0.2.0,10.0.15.254,infinite
>         dhcp-option-force=FABRIC,77,"FABRIC"
>         
>         # ----- Configure PXE
>         dhcp-option-force=208,f1:00:74:7e
>         dhcp-option-force=209,default.cfg
>         dhcp-option-force=210,/std/var/boot/
> 
> This works fine and has for many months now.  But, sometimes I have a
> need for one particular system to boot a separate image, with a
> different config file.  When this happens I add a NEW file
> to /etc/dnsmasq.d, then restart the service; the new file contains this:
> 
>         dhcp-host=00:06:72:00:01:09,net:replace
>         dhcp-host=00:06:72:01:01:09,net:replace
>         dhcp-host=00:06:72:FF:F9:9D,net:replace
>         dhcp-host=00:06:72:FF:F9:9E,net:replace
>         dhcp-boot=net:replace,/alt/update_bundle/pxedir/pxelinux.0
>         dhcp-option-force=replace,208,f1:00:74:7e
>         dhcp-option-force=replace,209,default.cfg
>         dhcp-option-force=replace,210,/alt/update_bundle/pxedir/
> 
> (the system has 4 nics and I'm not sure which one will do the PXE boot
> request so I set all 4).  Here I assign a network ID to the 4 MACs, then
> I specify a different boot file and PXE config file for just this
> network ID.  This worked at least once, but now is not working anymore
> and I cannot figure out why.
> 
> The oddest thing is that the boot file IS replaced; I can see on the
> boot line that it loads the /alt/update_bundle/pxedir/pxelinux.0 image,
> but the PXE configuration options are wrong; they are still the ones
> from the main configuration, not the ones specific to the network ID.
> 
> I've sniffed the interface on the DHCP server with tcpdump and viewed
> the output and I can confirm this concretely: the dnsmasq server is
> sending back the correct boot file (i.e., the dhcp-boot override works
> fine) but the wrong PXE elements (i.e., the three dhcp-option-force
> items are not taking effect).
> 
> I've checked syslog and I don't see any odd messages from dnsmasq, and
> I've looked through the man pages to verify my syntax and for some kind
> of extra debugging to turn on that might show info on how dnsmasq is
> choosing the network ID or whatever, but no luck.
> 
> 
> I'm using the default dnsmasq instance that comes with Red Hat
> Enterprise Linux 5.3, which is:
> 
>         Dnsmasq version 2.39  Copyright (C) 2000-2007 Simon Kelley
>         Compile time options IPv6 GNU-getopt no-ISC-leasefile no-DBus no-I18N TFTP
> 
> Help!!  I need to get this working quickly.  I'm sure it's something
> very stupid but I can't figure it out :-/.
> 

OK, quick fix to try. Modify yout default PXE options to have a netid of
"#replace", eg

dhcp-option-force=#replace,210,/std/var/boot/

That way they can't be used when the "replace" tag is set.

2.39 is pretty old. Is it possible to upgrade to a newer version? Bugs
have been fixed in this area.

Cheers,

Simon.