Most common challenges and solution with Availability group listener and multisubnetfailover

Industry started using SQL availability groups on most of their environments, DBA is coming across multiple issues related to AGListener connectivity.

This blog explains 2 major challenges and solutions in detail:
https://blogs.msdn.microsoft.com/alwaysonpro/2014/06/03/connection-timeouts-in-multi-subnet-availability-group/

I recommend option-1 to enable client to use multisubnetfailover option to experience seamless fail over. If this is not feasible for any legacy reasons use option-2 to make sure AGListername is configured with single IP in DNS and change the TTL to shorter duration (Example: 1 minutes; Assuming a maximum 1 minute downtime is accepted)

To Summarize different categories:
1. MultiSubnetFailover is missing (Ref: https://blogs.msdn.microsoft.com/alwaysonpro/2014/06/03/connection-timeouts-in-multi-subnet-availability-group/)
2. Client is not capable of using multiSubnetFailover, register Single IP in DNS – Ref: https://blogs.msdn.microsoft.com/alwaysonpro/2014/06/03/connection-timeouts-in-multi-subnet-availability-group/
3. TransparentNetworkIPResolution resulting timeout after 500 ms for DNSlookup.
Resolution is to set this property to false (This is only after .NET Framework 4.6 or later) Ref –
https://blogs.msdn.microsoft.com/dataaccesstechnologies/2016/05/07/connection-timeout-issue-with-net-framework-4-6-1-transparentnetworkipresolution/

How to find .NET Framework version: https://docs.microsoft.com/en-us/dotnet/framework/migration-guide/how-to-determine-which-versions-are-installed

Additional resources:
https://technet.microsoft.com/en-us/library/dd197575(v=ws.10).aspx

https://docs.microsoft.com/en-us/sql/sql-server/failover-clusters/windows/sql-server-multi-subnet-clustering-sql-server

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