Comtrend Corporation NexusLink 3120 User Manual page 218

STEP 3: This screen provides access to NAT, Firewall and IGMP Multicast settings.
Enable each by selecting the appropriate checkbox .
Click Next to continue or click Back to return to the previous step.
ENABLE NAT
If the LAN is configured with a private IP address, the user should select this
checkbox . The NAT submenu will appear in the Advanced Setup menu after
reboot. On the other hand, if a private IP address is not used on the LAN side (i.e.
the LAN side is using a public IP), this checkbox  should not be selected, so as to
free up system resources for improved performance.
ENABLE FIREWALL
If this checkbox  is selected, the Security submenu will be displayed on the
Advanced Setup menu after reboot. If firewall is not necessary, this checkbox 
should not be selected so as to free up system resources for better performance.
ENABLE MLD MULTICAST PROXY
Multicast Listener Discovery (MLD) is a component of the Internet Protocol Version
6 (IPv6) suite. MLD is used by IPv6 routers for discovering multicast listeners on a
directly attached link, much like IGMP is used in IPv4. The protocol is embedded in
ICMPv6 instead of using a separate protocol.
ENABLE MLD MULTICAST SOURCE
Click to allow use of this WAN interface as Multicast Listener Discovery (MLD)
multicast source.
Enable WAN interface with base MAC
Enable this option to use the router's base MAC address as the MAC address for this
WAN interface.
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