Failover and pools with single machines

John Wobus jw354 at
Thu Dec 14 19:37:19 UTC 2006


If, as you say, you need the lease to be in the lease file, is there 
some specific
use to which you put this file that determines what data must be in it? 
could be crucial.

I think Simon's proposed solution will work as advertised, but will show
different-looking lease-file entries on the two servers.  Using a 
pool, the two lease files will show consistent data except during short
transition times.  On the other hand, with non-failover (independent) 
pools, as
Simon suggested, the lease files can more often hold differing 
information: one
lease file showing the address assignment while the other does not.

FYI, I experimented with very small failover pools and ran into exactly
what Simon stated about small pools.  Three addresses appeared to be the
minimum size to make them function.  I suspect some ISC development 
make the server software "handle" two- and one-address pools, but such 
would hardly be generally useful.

John Wobus
Cornell CIT

On Dec 14, 2006, at 11:01 AM, Tina Siegenthaler wrote:

> Am 14.12.2006 um 16:52 schrieb Simon Hobson:
>> Tina Siegenthaler wrote:
>>>> Failover won't work with such small pools. However, since you will
>>>>  only have one client/pool then you could simply replicate the
>>>> config
>>>>  and NOT use failover. The client will get the same address
>>>> regardless
>>>>  of which server it took the lease from, and no other client will
>>>> get
>>>>  the same address from the other server.
>>>>  You would still need to use failover on the general use pools
>>>> though.
>>> Does this mean I can just use the same config file (or that part of
>>> it with the single-host pools) on 2 dhcp servers at the same time?
>>> Won't they get each other in the way?
>> Ordinarily, having two independent servers offering the same
>> addresses would be a disaster looking for somewhere to happen. It
>> will work in this case because you have pools with exactly one
>> address which can be leased to exactly one client - so you can't have
>> the same address offered to two different clients.
> Now, I see. That's why I was sceptic, because usually having 2 dhcpd
> servers on the same network is not really what you want to have...
> So I'll give this setup a try.
> Thanks again for your help,
> Tina

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