MNET CLI Configuration sample:

SJ-Box1(config)#mnet inside mnet1
SJ-Box1(config)#ip address mnet1 192.168.1.1 255.255.255.0
       

Webui Array OS 6.4 or later in Mode "config":
Under "System configuration" -> Basic Networking -> "Interface" tab -> port -> under "interface configurations" -> Mode "MNET"