What network ports need to be open for SQL Server to accept connections?

For a default SQL Server instance, TCP port 1433 is typically used. For named instances, SQL Server uses dynamic ports by default. In this case, the SQL Server Browser service (UDP port 1434) needs to be running on the server to inform the client which dynamic TCP port the SQL Server instance is using. Ensure these ports are open in any firewalls between the client and the server.