Hosting applications in Azure usually requires some form of connection to the on-premises networks. You could use Point-to-Site dialup or ExpressRoute, but Site-2-Site VPN’s seems the most use technology, and certainly is cheaper than ExpressRoute connection.
But what if you want to use multiple links for failover? What if your local firewall fails or the internet connection itself? Well, that’s why Azure supports MultiSite VPN’s. While it is capable of having two tunnels from on-premises to Azure with preferences, there is no automatic failover support. That means that if tunnel 1 goes down, tunnel 2 is NOT automatically activated. You need to disable tunnel 1 in Azure itself and only THEN tunnel 2 comes up. Which is annoying, but there is another way to fully automate this.. BGP, Border Gateway Protocol.