ISC DHCPD giving out reserved IPs for non-reserved hosts

Simon Hobson dhcp1 at
Mon Jul 9 21:24:49 UTC 2007

John Wobus wrote:

>All I say is that the 'host' declaration in the ISC server is not the
>exact equivalent of the 'reserved' feature in the Microsoft server.
>To mimic Microsoft's 'reserved' configuration feature, in the ISC
>server you would also need to declare a dynamic pool or pools
>specifying which addresses are to be dynamically given out.
>Microsoft wins for configuration convenience in this specific case,

I disagree - see below

>though many would not directly mess with the ISC configuration, but
>would use software to construct the file, which could take care of
>such complications under the covers, and perhaps offer other
>configuration convenience features that Microsoft doesn't.
>(I actually have zero experience with the Microsoft server, so
>I could easily go off track and say something wrong about it.)

The main reason people configure MS servers with the whole subnet and 
then reserve parts of it is because the implementation is totally 
brain dead - you cannot EDIT things ! Once you have configured a 
scope (akin to a range in ISC terminology) then you cannot edit it, 
only delete it and add it back. The result is that people simply 
configure the entire subnet as dynamically assignable and then 
reserve the bits they don't want handing out. Even then, you cannot 
edit a reservation (only delete it and add it back with a different 
range) but at least it doesn't have any options to reconfigure unlike 
the scope.

Oh yes, and it's not RFC compliant in several areas - just in case 
that's a surprise !

People really should learn how to drive the MS server, then they'd 
appreciate the flexibility of the ISC config file ;-)

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