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Edit dhcp failover group
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This edit form allows you to create relationships between two existing hosts within ONA. You would select a primary and a secondary server by providing the FQDN of the hosts that will service DHCP. A single server can be part of many failover groups but the two together must be a unique paring.
The other options should work fine using the default values. Please refer to the DHCP documentation for an explanation of what each value is for.
The most likely option you may change is the
split value. The default of 255 implies that the primary server should service all IPs from the subnet and the secondary server will only be involved if the primary is down. Another common split is
128 to allow for a 50/50 split between the two servers.
Failover groups are only applicable to DHCP Pools. A subnet that has MAC based assignments will be available on all servers you have the subnet associated with. Only the Pools will be influenced by the failover group settings. To that end, once you have a failover group defined, you must then go to each DHCP pool and choose the appropriate failover group to apply them to. A pool is not required to be part of a failover group.
Also, prior to setting up a failover group you must ensure that ports 647 and 847 are reachable between the two DHCP servers. You can verify this by executing
telnet <servername> 647 from both servers toward the other server. Do this for both ports.
You must also ensure that at least one DHCP pool is associated with this failover group. If you do not, your current DHCP configuration will fail with an error.