The question "How does DNS Failover work?" is not easily answered in one sentence. There is a lot that goes on behind the scenes, but we'll do our best to explain it.
First, DNS Failover is designed to automate changing of DNS records based on the availability of different devices. Suppose you have two web servers. One at 203.0.113.5 and another at 203.0.113.6. In a normal DNS configuration, if you wanted traffic to go to both servers, you would create an 'A' record for both of them. In that way, traffic is round-robin load balanced between the two.
But what happens if a device goes down or stops responding in a timely fashion? In a normal scenario, you'd have to first be alerted to the problem. Then you'd log into DNS and remove the 'A' record for the device that needs to be taken out of service. This process requires external monitoring services or systems, and it also requires you to manually make a change. This can result in a prolonged outage, or in the case of two active servers, 50% of your users being directed to a server with problems.
Netriplex DNS Failover automates this entire process. Instead of using an external monitoring service to alert you (although you still can), you would use Netriplex's built-in device monitoring system. It will check your device at pre-programmed intervals (that you configure) using any number of accurate monitors such as a ping check (our least favorite) to an HTTP GET for a response code, HTTP get for content on a page or even SNMP for server health. Once the monitoring detects a diversion from the expected results, it automatically triggers a DNS update event to take the device out of DNS resolution rotation. This can generally be done in 2 to 3 minutes and works very well.
Of course, you don't need to use DNS Failover for round-robin delivery of users to many active servers. It can be configured for an active/standby or active/failover situation as well. That is, we can send all traffic to a single IP address, and only when that goes down do we send the traffic to a failover/backup IP address. Furthermore, we can create multiple levels. So we could fail even to a third or fourth IP address as well. That way you can fail from your primary device to a secondary, and if both fail, even to a disaster recovery/business continuity site. We can also fail from a round-robin group of servers to a single backup/failover or DR/BC server.
DNS Failover can be quite powerful, so do not hesitate to reach out to our sales or support teams for further ideas on how we can help you solve your particular challenge. And yes, DNS Failover works not only with IPv4 address space, but IPv6 as well!