Correct Failover / DHCPOFFER functionality

David W. Hankins dhankins at
Tue Jun 30 19:30:30 UTC 2009

On Mon, Jun 29, 2009 at 05:17:02PM -0400, Robert Hille wrote:
> I had thought that (if configured correctly) when a pair of dhcp servers  
> were in failover  mode, each would answer the request based on balancing 
> spec'ed in RFC 3074.

LBA is only performed on DISCOVER, if the client's 'secs' field is
less than the configured 'load-balance-max-secs', then one server
will elect not to respond based on the hash results.

On REQUEST, the servers will always answer if they are able to, for
example if the lease is active.  The sources include a lengthy
comment by their originator that claims this is an optimization to
avoid sending the client(s) through unneccessary state changes, if
my memory serves.

There is an appearance of load balancing when the clients are not
requesting a previously-active binding; if the lease is in the free
or backup states, only their respective servers can safely process
the request, and so only one server answers.  This is not elective
in DISCOVER's case, however.

David W. Hankins	"If you don't do it right the first time,
Software Engineer		     you'll just have to do it again."
Internet Systems Consortium, Inc.		-- Jack T. Hankins
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