Install ConfigMgr 2012 Clients on DMZ workgroup servers

Last week I did some ConfigMgr client installation on DMZ workgroup servers. Installation of the client went fine, but they went on internet mode after that. There was no possibility to add them to a Site either. Looking in locationservices.log the following lines were showed:
-Failed to resolve 'SMS_SLP' from WINS
-Unable to find lookup MP(s) in Registry , AD, DNS and Wins
-LSIsSIteCompatible: Failed to get Site version from all directories.
-failed to get dp locations as the expected version from mp

The installation line used was as follows:
Ccmsetup.exe /mp:<FQDN> /logon SMSSITECODE=XXX FSP=<FQDN>

After a few installations I found the following website:
About Client Installation Properties in Configuration Manager 2012

It mentions:
/source:<Path> = Specifies the location from which to download installation files. You can use a local or UNC installation path. Files are downloaded by using the server message block (SMB) protocol.
/mp:<Computer> = Specifies the source management point for downloading installation files. Files are downloaded over an HTTP or HTTPS connection, depending on the management configuration for client connections. This download uses BITS throttling, if BITS throttling is configured. If the management point is configured for HTTPS client connections only, you must verify that the client computer has a valid PKI client certificate.
/logon = Specifies that the client installation should stop if any version of the Configuration Manager 2012 or SMS client is already installed.
SMSMP = Associates the Configuration Manager 2012 client with the specified management point. You can specify a fully qualified domain name as this property.

In the end I used the following installation line to install ConfigMgr 2012 Clients on DMZ workgroups servers successfully:
Ccmsetup.exe /source:<path> SMSSITECODE=XXX FSP=<FQDN> SMSMP=<FQDN>

Hope it helps!

Source:
Install SCCM 2012 Client on DMZ workgroup servers
Managing workgroup clients in Configuration Manager 2012