For Ubiquiti then the person to ask is
@jeyare
To maintain Internet access through the router when one WAN connection fails then there are at least a couple of approaches:
- If the router can handle two active WAN connections then you can have an Internet DNS service advertise both connections separately: acc1.mydomain.com and acc2.mydomain.com. If you have a DNS load balancing service on the Internet then you can prioritise NAS services (subdomains) down either acc1 or acc2, and then acc2 and acc1 as a backup. Here the DNS load balncing server is performing the failover by detecting the prioritised path is down and returning the backup path.
- If you have active/passive WAN where the router is doing the failover itself then you will have to modify your DNS records to advertise the new IP address to your router.
Option 1 will likely be for businesses that either subscribe to such a service, or have deployed hosted devices such as F5 BigIP DNS (formerly GTM).
For option 2, for traditional DNS services and Time-To-Live, it can take up to three days for DNS changes to be fully replicated globally. By using DDNS services that have short TTL then you can use either router, DSM, or server/client software agents to monitor Internet IP changes and then update your DDNS records. These changes will then propagate quickly.