Enabling remote access to a SQL Server

Configure the remote access option

1. In Object Explorer, right-click a server and select Properties.
2. Click the Connections node.
3. Under Remote server connections, select or clear the Allow remote connections to this server check box.

Configure 'SQL Server Configuration Manager'

1. On the SQL Server, open 'SQL Server Configuration Manager'. This can typically be found linked from the 'Start' menu. For example: Start | All Programs | Microsoft SQL Server 2008 R2 | Configuration Tools | SQL Server Configuration Manager.
2. Expand 'SQL Server Network Configuration' and highlight the 'Protocols for [InstanceName]' option.
3. In the right-hand window, if 'TCP/IP' currently has the 'status' of 'Disabled', right click on 'TCP/IP' and select 'Enable'.
   Note: You will be requested to restart the SQL Server service to complete the configuration change.
4. Enable access to port 1433 (the port used by SQL Server) on the db server via Windows Firewall and any network-level firewalls.
5. To restart the service, you can use the same Microsoft Management Console (MMC) window. To do so, highlight the 'SQL Server Services' option at the top of the tree. In the right-hand window, you can then right click on the 'SQL Server [Instance]' entry and choose 'Restart'.

If you still cannot connect, turn off your firewall and try again

Source:
http://technet.microsoft.com/en-us/library/ms191464.aspx
http://www.sophos.com/en-us/support/knowledgebase/118473.aspx

http://stackoverflow.com/questions/13777680/sql-server-2012-remote-access-outside-domain