Dual DNS server farms in dhcpd.conf

Frank Bulk frnkblk at iname.com
Wed Apr 29 02:44:53 UTC 2009

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
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