Dual DNS server farms in dhcpd.conf

Glenn Satchell Glenn.Satchell at uniq.com.au
Wed Apr 29 03:13:13 UTC 2009

If your hosts never move to other subnets then they will probably be
ok. But if one was to be moved (eg a laptop is an example) then it
will inherit options from the shared-network, whatever they may be.

In your mind it might tie these hosts to the network, but to dhcpd it
just tells it where to inherit options from.


>From: "Frank Bulk" <frnkblk at iname.com>
>Date: Tue, 28 Apr 2009 21:44:53 -0500
>We have a GUI front-end to our DHCP configuration, and we like to keep our
>host definitions organized as opposed to clumping them all in the global
>scope.  We've always placed our hosts in the shared-subnet without issues.
>But the GUI shows what's inherited because it's location in the
>-----Original Message-----
>From: dhcp-users-bounces at lists.isc.org
>[mailto:dhcp-users-bounces at lists.isc.org] On Behalf Of Simon Hobson
>Sent: Tuesday, April 28, 2009 1:30 PM
>To: Users of ISC DHCP
>Subject: RE: Dual DNS server farms in dhcpd.conf
>John Tabasz (jtabasz) wrote:
>>So I understand properly,  when you say putting
>>the host statements inside a scope other than global isn't generally a
>>good idea, you are referring to the shared network scope plus the second
>>scope of the subnet, right?
>Exactly. In your config, the host statements are inside the 
>shared-subnet - a case we haven't come across before so I'm not 
>entirely sure what happens here. A couple of times, user have put 
>host statements inside a subnet declaration (erroneously) thinking 
>that this would make the statement valid only within that subnet. 
>They've them come to the list wondering why a client gets an IP 
>address, but other options (such as routers !) from the wrong subnet 
>when the client is connected elsewhere.
>What's happened in that case is that the client gets an IP according 
>to the subnet where it is connected, but inherits options from the 
>subnet where it's declared. Hence we keep advising to keep host 
>statement in the global scope.
>I think in your case it **probably** isn't an issue since there are 
>no options declared at the shared-network level - but best to avoid 
>it anyway.
>Simon Hobson
>Visit http://www.magpiesnestpublishing.co.uk/ for books by acclaimed
>author Gladys Hobson. Novels - poetry - short stories - ideal as
>Christmas stocking fillers. Some available as e-books.
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