Hi,
If using SEP 12.1 then it's more advance to use virtualize network compared to SEP 11.
SEP 12.1 have feature like shared insight cache, Virtual client tagging etc.
https://www-secure.symantec.com/connect/blogs/shared-inside-cache-sep-121
Symantec Endpoint Protection 12.1 - Virtualization Best Practices
http://www.symantec.com/docs/TECH173650