Failover and duplicate DHCPACKs

David W. Hankins dhankins at
Mon Mar 1 17:21:23 UTC 2010

On Mon, Mar 01, 2010 at 05:03:27PM +0200, Kimmo Liikonen wrote:
> I  am wondering that why ISC DHCP server works differently with some other
> clients?

It isn't a difference in clients you're citing, it's a difference in
lease state.  Free or backup leases can only be allocated to active by
one of the two servers (unless only one server is operating in
partner-down and STOS+MCLT has expired).

Active leases have been assigned to a client and will retain that
assignment until the servers negotiate expiration, so failover allows
both servers to extend any active lease.  Our implementation strategy
assumes a DHCPREQUEST on an active lease is potentially an indication
the client can't communicate effectively with the peer, failover
connection state notwithstanding, so it is best in that case to
answer expediently.

David W. Hankins	BIND 10 needs more DHCP voices.
Software Engineer		There just aren't enough in our heads.
Internet Systems Consortium, Inc.
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