address pools

[Glenn Satchell]

>From: "Chris Miller" <Chris at InfoGreat.com>
>To: <dhcp-users at isc.org>
>Subject: RE: address pools
>Date: Thu, 16 Nov 2006 06:25:33 -0800
>
>Hi Simon,
>
>THANKS THANKS THANKS THANK THANKS and yet again THANKS  for the comments.
>:-)
>
>I did discover classes and I'm aware that I can "allow" and "deny' members
>of <class> in the pools, but it is not clear haw I assert that my hosts are
>members of <class>.  The doc show lots of ways to interrogate options that
>are already there but I'm hoping I can do something like:
>
>	Host trax {hardware ethernet XX:XX:XX:XX:XX:XX; class "servers"' } 
>
>... or even 
>
>	Host trax {hardware ethernet XX:XX:XX:XX:XX:XX; class "servers"';
>class "static"; class "infrastructure"} 
>
>... but I've found nothing that hints at this.  Google was no help either.

Keep reading :) a bit further down in the dhcpd.conf man page it talks
about Sub-Classes. This is what you want.

     class "servers" {
       match pick-first-value (option dhcp-client-identifier, hardware);
     }

     class "infrastructure" {
       match pick-first-value (option dhcp-client-identifier, hardware);
     }

     subclass "servers" 1:8:0:2b:4c:39:ad;
     subclass "infrastructure" 1:8:0:2b:a9:cc:e3;
     subclass "servers" 1:0:0:c4:aa:29:44;

Note the '1' at the beginning of the mac address in the subclass - it's
the media type, and 1 is ethernet.

>This was why I thought if I declared my host in the scope of the pool, that
>their address would be allocated from that pool -- not really so silly, you
>see.  And the docs are quiet good at one level, but there is a larger
>context that is not clear -- as evidenced by some of my confusion.  All the
>statements and options are clearly explained but the higher level discussion
>of how to assemble them to achieve certain goals is not at all clear.
>Unless I'm reading the wrong docs ...  ?

A host declaration is a bit smarter than that, because a host could
potentially have different addresses, eg if it was a laptop that moved
to different subnets.

There is an excellent book: The DHCP Handbook by Ted Lemon and Ralph
Droms, now in 2nd Ed. Ted was the original author of the ISC dhcpd, and
Ralph was/is the chair of the IETF DHC Working Group, so they both know
a fair bit about dhcp :)

regards,
-glenn