DHCP Redundancy
the Radio
theradio at free.fr
Sun Nov 28 10:49:10 UTC 2010
"If one fails, the other can take over and manage the full address space."
Be warned that only HALF of the address space is "automatically" taken
over by the surviving DHCP process (assuming the failover team consists
of 2 servers) :
/"If one server fails, the other server will continue to renew leases
out of the pool, and will allocate new addresses out of the roughly half
of available addresses that it had when communications with the other
server were lost. "/
v4.2.0-P1 option "auto-partner-down" does not work for now, then
imposing to MANUALLY edit the leases file to set the surviving server
into "PARTNER-DOWN" state (see dhcpd.conf help file).
Therefore, the failover efficiency depends greatly on the clients
requests rate : I had a big wireless infrastructure that, whenever a
controller shuts down, half of the 1000 APs request their address back -
until you have a more than 2000 addresses subnet, some APs do not get
their IP.
My main advice concerning failover (until partner-down state is really
automatized) : use subnets large as twice as needed (if you have 200
expected clients, set for a /23 subnet at least).
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