Frustrated DHCP failover not working.. :(

Shawn Routhier sar at
Wed Feb 10 19:59:25 UTC 2016

> On Feb 10, 2016, at 11:37 AM, Attila Szalay <mochrul at> wrote:
> In the master node, you have this configuration option: split 128;
> This means, that half of the ip addresses are linked to the master and the secondary only own the other half.

This isn’t quite correct.  The split option refers to how the two servers
handle incoming requests not how they allocate addresses between
them.  128 is splitting the hash buckets used to divide the clients
50 / 50.

> Of course time-to-time they rebalance the ip pools, but (if I remember correctly) it only happens after a timeout. So if the clients only reach one of the hosts, it is possible, that those host (temporally) run out of hosts.

The load balancing algorithm is used until the seconds field in the
request packet exceeds the value specified by “load balance max seconds”
at which point either of the two servers will respond.  As the seconds field
is the amount of time since the client started to request it will normally be
0 to start with and increment if there are time outs.

> This is because in normal operation (and with split 128, which means 50-50%) they run more likely as a load-balancing scenario than master-slave. (Also they split the mac address word to half too and the slave answer to one half of the macs and the master to the other))

On the original question.  Setting your MCLT to 30 minutes while your default lease time is 20 minutes
seems a bit strange to me.


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