Problems with pool balancing.

[Erling Paulsen]

Hello,

We have two servers in failover relationship, both running 
isc-dhcp42-server-4.2.4_2 on FreeBSD 8.3-RELEASE-p7 and we are having 
problems with balancing the pools when pool-usage climbs into the higher 
figures.

Example (numbers from logfiles at about the same timestamp):

Master: total 3905  free 1  backup 512  lts -255
"lts" is correct according to the the documentation at (free - backup)/2 
= -255
Since "leases to share" is negative, the master expects the secondary 
server to hand over leases!

Secondary: total 3905  free 513  backup 0  lts -256
"lts" is correct according to the the documentation at (free - backup)/2 
= -256

They do seem to have the same understanding of the current lease 
situatioon. But! "lts" on secondary is also negative, so it's also 
expecting the master to hand over leases!

This cannot possibly end well?

This is what's in the source-code and it seems to comply with the 
description:

                 if (p->failover_peer->i_am == primary) {
                         lts = (p->free_leases - p->backup_leases) / 2;
                         peer_lease_state = FTS_BACKUP;
                         /* my_lease_state = FTS_FREE; */
                         lq = &p->free;
                 } else {
                         lts = (p->backup_leases - p->free_leases) / 2;
                         peer_lease_state = FTS_FREE;
                         /* my_lease_state = FTS_BACKUP; */
                         lq = &p->backup;
                 }

I don't understand what can be the cause of the double-trouble negative 
lts on both sides! And, btw, can someone shed a light on how the 'lq' 
pointer affects the balancing?

Anyone have thoughts of what might be the culprit here?
Any information would be appreciated.


- Erling Paulsen

-- 
---------------------------------|sent-av|-----
Erling Paulsen, Seksjon for Infrastruktur/Nett
TEO 2.402, Universitetet i Tromsø, 9037 TROMSØ  .
Kontor (+47) 77 64 64 80 Mob (+47) 91 17 64 01 ..: