Hello,
Please check this Thread: https://www-secure.symantec.com/connect/forums/server-dmz
and check these Articles:
Best Practices: Configuring a Symantec Endpoint Protection environment in a DMZ
http://www.symantec.com/business/support/index?page=content&id=TECH178325
Security recommendations regarding SEP client installed on server located in DMZ
http://www.symantec.com/docs/TECH122858
Communication issues with SEP client installed in DMZ while the SEP Manager is outside DMZ
http://www.symantec.com/docs/TECH146736
Updating downloads in an internal LiveUpdate Administrator 2.x Server using the downloads from an external LiveUpdate Server
http://www.symantec.com/docs/TECH106254
NOTE: The above Articles applies to both SEP 11.x and SEP 12.1
Hope that helps!!