Problems with DHCP using VLANs

Simon Hobson dhcp1 at
Thu Aug 27 17:56:26 UTC 2009

Tim Gavin wrote:
>  > Actually, /etc/default/dhcpd3-server does NOT override
>>  /etc/dhcp3/dhcpd.conf. It provides command line options for the startup
>>  script in /etc/init.d to pass to the server.
>>  You either need a config file (and /etc/default is standard on Debian based
>>  systems) or you end up hacking the startup scripts to set options.
>The standard /etc/dhcp3/dhcpd.conf was there, as was
>/etc/default/dhcpd3-server .  The 'default' script had an INTERFACES=
>line, as did the dhcpd.conf, and the one in the 'default' script was
>taking precedent somehow.  That was the only info in that script, so I
>just deleted it and took out the reference to it in

OK, it seems you didn't pick up on what I wrote. A list of interfaces 
is passed as command line arguments, NOT picked up from dhcpd.conf 
(where a line with "interfaces=" should have been flagged as an 
error). The two files serve DIFFERENT functions and both are needed.

In /etc/init.d/dhcp3-server, the key bit is :
>		start-stop-daemon --start --quiet --pidfile $DHCPDPID \
>			--exec /usr/sbin/dhcpd3 -- -q $INTERFACES
here $INTERFACES is passed as command line arguments when dhcpd3 is 
started. Without /etc/default/dhcpd3-server (or another file to do 
the same job) then you would have to edit the script itself which 
could potentially cause problem when upgrading. Once you edit a 
script, an upgrade may mean choosing between throwing away your 
changes or keeping an old (and potentially sub-optimal) script.

Obviously different people have different preferences, since I almost 
exclusively use Debian I find their way of doing things comes 
naturally to me.

Had ISC decided to put the interface list in the main conf file then 
we wouldn't be having this discussion - I assume they had their 
reasons for that choice. Other command line arguments need to be 
separate - you can't specify the config file to use in the config 
file ! For most people, the compiled in defaults will do most of the 
time, if not all.
Simon Hobson

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