After you have installed SQL Server, you might have noticed that the firewall will block access to it.
In order to remedy this, you will have to open 2 ports in the firewall.
TCP port 1433 for the actual SQL Server engine, and UDP port 1434 for the SQL Server Browser.
This could be done from the GUI, but I have found that it’s more convenient to do it from an elevated command prompt.
netsh firewall set portopening protocol=TCP port=1433 name = SQLPortEngine mode=ENABLE scope=SUBNET profile=CURRENT netsh firewall set portopening protocol=UDP port=1434 name = SQLPortBrowser mode=ENABLE scope=SUBNET profile=CURRENT
Or follow the manual GUI steps in this MSDN article:
How to: Configure a Windows Firewall for Database Engine Access