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