When creating a failover pool in DNS Failover you are given the opportunity to specify a monitor for each IP address that is a member of the pool to detect whether or not the IP is available (online) and can be used for the corresponding ‘A’ or ‘AAAA’ record when required. To recap, in roundrobin mode, all failover IPs that are UP are utilized. In sequential mode, only the failover IP with the lowest priority (e.g. 1) that is UP is utilized.
In the event that none of your IP addresses pass a monitoring test, the ‘A’ or ‘AAAA’ record is completely removed from DNS. This is by design. However, if you do not wish for this to happen, you may want to disable monitoring for your highest priority IP address (last to be utilized when in sequential mode). This will allow the DNS failover system to always see that device as up and available, regardless of whether or not that is the case. In this scenario, should the first IP address go down, the second will be replaced for the corresponding ‘A’ or ‘AAAA’ record in DNS regardless of its true state.
If you’d rather have the primary IP given out in DNS during this situation, then we would recommend configuring your primary and secondary IPs as normal failover pool entries (assuming you only have two) and then add a tertiary IP that is identical to the primary IP but without monitoring enabled. This will ensure that if both the primary and secondary IP addresses fail a monitoring test, the tertiary (which is really the same as the primary) will be given out in DNS anyway.