Beware: change in configuration file semantics

[Niall O'Reilly]

	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 server.example.net;
     }

	This is no longer possible, as the semantics of the reference appear
	to have been changed, at least in v3.1.0.  Specifically, the option
	name specified in the reference is not used as it stands, but has an
	option-space (?) prefix 'dhcp.' attached before looking it up.
	Since parallel semantics are not used in interpreting the option
	declaration, an error message is generated, the configuration
	file is not loaded, and dhcpd exits.

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

	A work-around appears to be to use an explicit prefix when declaring
	the option, as in the example below.

     option dhcp.tftp-server-address code 150 = ip-address;

	This significant change in behaviour appears not to be mentioned
	in any of the following: release notes for v4.0.0, release notes
	for v3.1.0, and dhcp-options man pages for either of these versions.

	I may have missed something in my reading and Google-hunting, but
	I think I've done enough homework to ask the following questions.

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

	/Niall

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