dual DHCP servers

[Alistair Crust]

On Tue, 2007-04-10 at 13:23 +0900, Tomoki Taniguchi wrote:
> I am not sure this is the place to ask, but i am hoping someone on
> this list will know the answer.
> 
> What happens when you have two DHCP3 servers giving out dynamic IP on
> the same subnet.
> 
> One is set as the "authoritative" server and the other is not.
> 
> will the non-auhortitative server always defer to the authoritative?
> 
> will the non-authoritative server detect that the autoritative server
> is active and not respond to the DHCP request?
> 
> 
> TIA,
> Tomoki Taniguchi
> 

potentially you could end up with a mess here, long waits and headaches
wondering why a machine is not getting a lease.

"When a DHCP server believes that a client is requesting an address that
is not appropriate for the subnet to which it is attached, for example
because a user's laptop received a lease from their home network the
night prior, the server is expected to send a DHCPNAK in response to the
client's DHCPREQUEST. This causes the client to immediately fall back to
INIT state, forget its old lease, and start over from scratch as though
it never had one. Out of the box, on a default configuration, ISC DHCP
does not do this, and you are expected to configure 'authoritative;' on
a line somewhere in your dhcpd.conf if you want this behaviour."[1]

A good tip here is to read the failover section of man dhcpd or the
documentation here (http://www.isc.org/index.pl?/sw/dhcp/) as I guess
that's probably what your after.

The other option (and one that IMHO works quite well) is to split the IP
range into parts and have each server issue leases for its section of
the range.

-- 
Kind regards
Alistair Crust
Systems Administrator 
Skegness Grammar School 
Vernon Road 
Skegness 
PE25 2QS 
TEL: 01754 610000 (ext'852)
FAX: 01754 896875 

[1]http://www.isc.org/index.pl?/sw/dhcp/authoritative.php