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Controls endpoint filtering for packets of the TCP protocol.
DMZ Host
DMZ means "Demilitarized Zone." If an application has trouble working from behind the router,
you can expose one computer to the Internet and run the application on that computer.
When a LAN host is configured as a DMZ host, it becomes the destination for all incoming
packets that do not match some other incoming session or rule. If any other ingress rule is in
place, that will be used instead of sending packets to the DMZ host; so, an active session,
virtual server, active port trigger, or port forwarding rule will take priority over sending a packet
to the DMZ host. (The DMZ policy resembles a default port forwarding rule that forwards every
port that is not specifically sent anywhere else.)
The router provides only limited firewall protection for the DMZ host. The router does not
forward a TCP packet that does not match an active DMZ session, unless it is a connection
establishment packet (SYN). Except for this limited protection, the DMZ host is effectively
"outside the firewall". Anyone considering using a DMZ host should also consider running a
firewall on that DMZ host system to provide additional protection.
Packets received by the DMZ host have their IP addresses translated from the WAN-side IP
address of the router to the LAN-side IP address of the DMZ host. However, port numbers are
not translated; so applications on the DMZ host can depend on specific port numbers.
The DMZ capability is just one of several means for allowing incoming requests that might
appear unsolicited to the NAT. In general, the DMZ host should be used only if there are no
other alternatives, because it is much more exposed to cyber attacks than any other system on
the LAN. Thought should be given to using other configurations instead: a virtual server, a port
forwarding rule, or a port trigger. Virtual servers open one port for incoming sessions bound for
a specific application (and also allow port redirection and the use of ALGs). Port forwarding is
rather like a selective DMZ, where incoming traffic targeted at one or more ports is forwarded
to a specific LAN host (thereby not exposing as many ports as a DMZ host). Port triggering is a
special form of port forwarding, which is activated by outgoing traffic, and for which ports are
only forwarded while the trigger is active.
Few applications truly require the use of the DMZ host. Following are examples of when a
DMZ host might be required:
•
A host needs to support several applications that might use overlapping ingress ports
such that two port forwarding rules cannot be used because they would potentially be in
conflict.
•
To handle incoming connections that use a protocol other than ICMP, TCP, UDP, and
IGMP (also GRE and ESP, when these protocols are enabled by the PPTP and IPSec
ALGs ).
Enable DMZ
DMZ IP Address
Specify the LAN IP address of the LAN computer that you want to have unrestricted
Internet communication. If this computer obtains its address Automatically using DHCP,
Putting a computer in the DMZ may expose that computer to a variety of
security risks. Use of this option is only recommended as a last resort.
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