I've done this tons of time in 2008 but we went with our first 2012 install.
SQL Server 2012 on server 1
SharePoint 2013 Enterprise on server 2
TCPIP turned on as a client protocol
TCPIP set as a valid protocol and enabled
Firewall open/complete shut off
Tried host/IP
Can connect with same credentials through Management Studio on same box no problem, using Windows Credentials and the DB is set to use Windows Credentials.
Cannot access via SP or even via the 64 bit ODBC control panel, cannot connect.
I vaguely remember something about 2012 having something to do with IPv6 and connectivity issues but cannot find it.
Both VM's on same physical host, no network issues at all. In fact I installed SharePoint off of a share on the SQL Server.
Not sure what I'm missing, everything I'd do in 2008 was done in 2012 but for some reason not obvious to me its not working.