ScaleArc attempting connections to SQL Server over random port numbers


This article explains why ScaleArc can sometimes be observed to be attempting connections to SQL Server through what may be interpreted as random TCP port numbers as opposed to the configured user-defined port for MSSQL, usually 1433 by default.



The default instance of SQL Server listens for incoming connections on port 1433. By default, named instances (including SQL Server Express) are configured to listen on dynamic ports.

A SQL Server instance using dynamic ports will change the TCP port every time the Database Engine service starts up. If your SQL Server instance has dynamic ports configured, you may occasionally experience connection issues after a failover or database server restart due to the dynamic TCP ports differing from what is configured in ScaleArc.

When ScaleArc is trying to connect to a SQL Server instance that is not reachable, it will try both the default port and dynamic port hence the reason why some unfamiliar TCP port numbers can be seen in the logs; the dynamic port range is usually high numbers up to a maximum of 65535 to avoid conflict with Well-Known and Registered ports.

To mitigate this issue and avoid connection failures, it is recommended that you configure only static ports for your SQL server instances. Check out this external article for step by step instructions on how to Configure a Server to Listen on a Specific TCP Port.

Tip: It is easier to manage the perimeter firewall rules when using static ports.

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