Beware: change in configuration file semantics

David W. Hankins David_Hankins at
Wed Feb 13 16:38:01 UTC 2008

On Wed, Feb 13, 2008 at 12:42:14PM +0000, Niall O'Reilly wrote:
> 	Prior to ISC DHCP v3.1.0, it was possible to declare an option (for  
> example):
>     option tftp-server-address code 150 = ip-address;
> 	and subsequently to refer to that option as follows.
>     host ... {
>         ...
>         option tftp-server-address;
>     }

so far as i am aware, this is true of all present and future releases

>     /etc/dhcpd.conf line 53275: unknown option dhcp.tftp-server-address
>                 option tftp-server-address server.

i am unable to replicate this (using dhcpd -t) with any of the
versions 4.1.0a1, 4.0.1b1-HEAD, 4.0.0, 3.1.1b1-HEAD, or 3.1.0, some of
which have yet to be released.  none complain.

> 	Was this change intended?
> 	If so, is it documented somewhere?
> 	Is the work-around I suggest likely to be safe?

i have a suspicion that you have found a typo in one of your config
files, or an extremely odd bug.

note that it has always been the case that an option foo declared

	option foo code bar = baz;

is implicitly a member of the DHCPv4 root options space - a DHCPv4
option code and format definition.  this means that the server has

1) substituded where 'option foo' lacks a dot.

2) installed into the 'dhcp option space' the option declaration for
   any 'foo' which lacks a dot.

so this is not new in any sense of the word between any current and
previous software version - the server has always assumed dhcp. when
it has been omitted, and the statements 'option tftp-server address'
and 'option dhcp.tftp-server-address' are completely equivalent.  i
don't know if the author intended this to save typing or to sound less
redundant (dhcp.dhcp-...) or what.

Ash bugud-gul durbatuluk agh burzum-ishi krimpatul.
Why settle for the lesser evil?
David W. Hankins	"If you don't do it right the first time,
Software Engineer		     you'll just have to do it again."
Internet Systems Consortium, Inc.		-- Jack T. Hankins

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