Kerio Tech KERIO WINROUTE FIREWALL 6 - Manual (Page 101)

7.8 Use of Full cone NAT
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Note: In the default configuration of the Traffic rules section, the Protocol inspector column
is hidden. To show it, modify settings through the Modify columns dialog (see chapter 3.2 ).
Warning
To disable a protocol inspector, it is not sufficient to define a service that would not use the
inspector! Protocol inspectors are applied to all traffic performed by corresponding protocols
by default. To disable a protocol inspector, special traffic rules must be defined.
7.8 Use of Full cone NAT
However, many applications (especially applications working with multimedia, Voice over IP
technologies, etc.) use another traffic method where other clients can (with direct connection
established) connect to a port “opened” by an outgoing packet. For these cases, WinRoute
includes a special mode of address translation, known as Full cone NAT. In this mode, opened
port can be accessed from any IP address and the traffic is always redirected to a correspond-
ing client in the local network.
Use of Full cone NAT may bring certain security risk. Each connection established in this mode
opens a possible passage from the Internet to the local network. To keep the security as high
as possible, it is therefore necessary to enable Full cone NAT for particular clients and services
only. The following example refers to an IP telephone with the SIP protocol.
Note: For details on traffic rules definition, refer to chapter 7.3 .
Example: SIP telephone in local network
In the local network, there is an IP telephone registered to an SIP server in the Internet. The
parameters may be as follows:
• IP address of the phone: 192.168.1.100
• Public IP address of the firewall: 195.192.33.1
• SIP server: sip.server.com
Since the firewall performs IP address translation, the telephone is registered on the SIP server
with the firewall’s public address (195.192.33.1). If there is a call from another telephone
to this telephone, the connection will go through the firewall’s address (195.192.33.1) and
the corresponding port. Under normal conditions, such connection can be established only
directly from the SIP server (to which the original outgoing connection for the registration was
established). However, use of Full cone NAT allows such connection for any client calling to
the SIP telephone in the local network.
Full cone NAT will be enabled by an extremely restrictive traffic rule (to keep the security level
as high as possible):