Failover strangeness

[David W. Hankins]

On Wed, Oct 11, 2006 at 12:28:30PM -0400, Greg G wrote:
>    STOS? I'm not familiar with that.  I see a reference to it in the 

"Start Time Of Service" - the time at which the server entered
a given state (in this case, partner-down).

>    The really strange things is that if the secondary goes down and the 
> primary complains, when the secondary comes back up, the primary takes 
> control of the lease again!

That sounds to be working as intended, for a one-lease pool whose lease
is in any state other than free or active, and a primary server that is
operating only in communications-interrupted state, or in partner-down
state where STOS+MCLT has not expired.

The alternate behaviour - taking the lease out of expired and back into
active if the peer last knew the lease to be active - is an optimization.

>     Hmmm.  I'm really looking for redundancy, so that either of the dhcp 
> servers can serve up the lease for these clients.   Both servers are
> getting the request (via ip-helper), and I don't want both of them
> offering the lease.  That could get ugly.

Actually even with failover there are known conditions when both
servers will answer...in communications interrupted when the client
is sensed to be in the INIT state.  I think both servers answer
when the client is REBINDING regardless of server state.

Clients deal with it well, and DHCP packet load is never significant.

Lots of people do this.  ISC's network does this.  No one reports
problems.

>    No joy, unless I did it wrong.  I put in the "infinite-is-reserved' 
> in the shared-network scope on both servers.

Probably the clients aren't requesting ininfinite lease-times...you
would have to try hand-editing dhcpd.leases.

That feature is still pretty experimental, and in an alpha quality
release of the software.  I'm not sure it's wisdom to encourage you
to follow this path.


By the way, that config option was intended to facilitate
experimentation with isc dhcp clients, where you can specify a
requested lease time, or any other similar client.  Just to get
some leases into the reserved state to see how they work.  There's
no really good real world use case for it I think.

-- 
ISC Training!  October 16-20, 2006, in the San Francisco Bay Area,
covering topics from DNS to DDNS & DHCP.  Email training at isc.org.
-- 
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