host statement scope rules (ISC DHCP 3.0.5b1)

Sten Carlsen sten at
Sat Jul 29 00:13:18 UTC 2006

I see the point. On the other hand, it does create a lot of
misunderstanding. Maybe a warning would be in its place, like proposed
by Glenn Satchell. Maybe a warning that could be turned off when you
really know what you do.

I believe that the lack of a message of some sort is responsible for
beginners believing they have really understood it and done the Right
Thing. Anyway this was just a passing thought, maybe it deserves a
little more consideration, at least the part of it that says: don't
allow constructs that misrepresent what they actually do.

Ted Lemon wrote:
> Glenn Satchell wrote:
>> Based on the number of posts to this list it appears that unfortunately
>> it is common practice to configure hosts entries this way. Enforcing it
>> in the way you propose would break a lot of configurations. Printing a
>> warning is a friendlier way to do this.
> Furthermore, if you know what you're doing, expressing a host statement
> in a non-global scope isn't an error.   You need to remember that in the
> DHCP configuration there are actually two sorts of scope: IP address
> configuration scope, and IP option configuration scope.   The two are
> tied together, but they aren't the same.
> The mistake people usually make with host declarations is to think "If I
> declare this in a subnet context, then it will only be in effect for
> hosts connected to that subnet, and will be ignored otherwise."   This
> is not true: a host declaration matches the intended host if no fixed
> address is present, or if a fixed address that is present is valid on
> the network to which the host is connected.   And for no other reason.
> However, a host declaration in a non-global context inherits the options
> and settings of the context in which it is declared.   So moving it to
> the global scope is not a neutral act - it's going to inherit different
> configuration settings and options if you do that.
> It might be better in the abstract to get rid of this dichotomy, but at
> this point I think it would cause as much confusion to get rid of it as
> it does to leave it the way it is.

Best regards

Sten Carlsen

No improvements come from shouting:


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