Different pools for dynamic and "static" leases

[Glenn Satchell]

>Date: Thu, 22 Mar 2007 09:14:55 -0400
>From: "Keith Lawson" <Keith.Lawson at sjhc.london.on.ca>
>
>>>> On Wed, Mar 21, 2007 at  2:40 PM, in message
><a06230912c2272c32399f@[192.168.0.149]>, Simon Hobson <dhcp1 at thehobsons.co.uk>
>wrote: 
>> Keith Lawson wrote:
>> 
>>>We've setup 2 pools in our subnet declarations. One pool is for 
>>>dynamic clients and the other is for "static" clients that have host 
>>>declarations with "fixed- address" options. We added the static pool 
>>>since our servers are configured in a failover pair.
>>>
>>>Ex:
>>>subnet 10.128.8.0 netmask 255.255.255.0 {
>>>    option routers...
>>>    # dynamic pool
>>>    pool {
>>>       options...
>>>       range 10.128.8.16 10.128.8.200;
>>>    }
>>>   # static pool
>>>    pool {
>>>      options...
>>>       range 10.128.8.201 10.128.8.250;
>>>}
>>>
>>>Is there a way to stop dynamic hosts from getting addresses out of 
>>>the static pool?
>> 
>> Yes REMOVE IT IMMEDIATELY !
>> 
>> You MUST NOT have an address which is both in a pool range statement 
>> and also allocated via a fixed address statement -  the server does 
>> NOT check and will quite happily give out an addresses to a dynamic 
>> client and later attempt to give the same address to the fixed 
>> address client.
>
>How does failover and load balancing function then if the static IP's aren't 
part of any range statement? 
>

If you're using fixed addresses then it makes no sense to have a range,
as the address offered is exactly the one in the fixed-address
statement.

For failover both hosts need to have the same host statements defined,
the client will receive a identical offers from all dhcp servers, and
can choose any of them. There's really no load balancing or failover
for fixed addresses as there is for dynamic pools, but the net effect
is there is still server redundancy.

subnet 10.128.8.0 netmask 255.255.255.0 {
  option routers...
  # dynamic pool
  pool {
    failover peer ...
    options...
    range 10.128.8.16 10.128.8.200;
  }
  # static pool
  options...
}

Note that the fixed-address hosts are not part of the pool, but are
part of the subnet, so they will inherit options fom the subnet, but
not from any pools within that subnet.

regards,
-glenn