|Windows firewall - connecting to a SQL instance||Friday 30th September 2016|
It seems that the Windows Firewall, by default, will stop you from being able to connect to a SQL instance - even when all outbound connections are allowed.|
The reason for this is because when connecting to an instance the SQL browser service is used. This operates over UDP (which is connectionless). A response is sent back from the browser service to the client machine, which is in-turned blocked by the client firewall.
To work around this you need to create a new rule that will allow UDP packets from port 1434. As with all rules, you should lock down the source to the smallest computer set you can (e.g. a single IP address) to avoid anything else from connecting.