If an ISP fails, it takes out whatever server is on its system. As to other issues the question is too broad so I decline to enter the tar pit question.
Here's a trap some IT staffers fall for. They worry about ISP failures and incur cost in both backup systems and lost time debating it all. As the tech lead at the office I shut down the discussion and redirect the IT to get on more pressing matters.
We have three internet services (WANs) terminated on one router. Router does load balancing as well as failover management. Some of our clients use RDP(port 3389) and remote login on daily basis. Those are all business users and they use "subdomain.mydomain.com" to connect with RDP session. There is A record in DNS Zone for "subdomain.mydomain.com" which is pointing to static IP of one WAN.
Considering this scenario, when one WAN (with the static IP that was set in above subdomain) fails then users cannot login. During such case we manually change A record and update the IP for the subdomain.
Someone suggested to create three A records for the same subdomain which are pointing to different IPs. Is this going to work when one ISP fails? Any other issues with this arrangement?
If you have any other better suggestion then please include in your replies.

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