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• Destination Port set to 5060 (the default SIP signalling port)
• Type set to TCP/UDP
3. Define four rules in the IP rule set:
• An Allow rule for outbound traffic from the clients on the internal network to the proxy
located on the DMZ interface.
• An Allow rule for outbound traffic from the proxy behind the DMZ interface to the remote
clients on the Internet.
• An Allow rule for inbound SIP traffic from the SIP proxy behind the DMZ interface to the
clients located on the local, protected network.
• An Allow rule for inbound SIP traffic from clients and proxies on the Internet to the proxy
behind the DMZ interface.
4. If Record-Route is not enabled at the proxy, direct exchange of SIP messages must also be
allowed between clients, bypassing the proxy. The following two additional rules are therefore
needed when Record-Route is disabled:
• An Allow rule for outbound traffic from the clients on the local network to the external
clients and proxies on the Internet.
• An Allow rule for inbound SIP traffic from the Internet to clients on the local network.
The IP rules with Record-Route enabled are:
Action Src Interface Src Network Dest Interface Dest Network
OutboundToProxy Allow lan lannet dmz ip_proxy
OutboundFromProxy Allow dmz ip_proxy lan lannet
InboundFromProxy Allow dmz ip_proxy core dmz_ip
InboundToProxy Allow wan all-nets dmz ip_proxy
With Record-Route disabled, the following IP rules must be added to those above:
Action Src Interface Src Network Dest Interface Dest Network
OutboundBypassProxy Allow lan lannet wan all-nets
InboundBypassProxy Allow wan all-nets lan lannet
6.2.9. The H.323 ALG
H.323 is a standard approved by the International Telecommunication Union (ITU) to allow
compatibility in video conference transmissions over IP networks. It is used for real-time audio,
video and data communication over packet-based networks such as the Internet. It specifies the
components, protocols and procedures for providing such multimedia communication, including
Internet phone and voice-over-IP (VoIP).
H.323 Components
H.323 consists of four main components:
Terminals
Devices used for audio and optionally video or data
communication, such as phones, conferencing units, or
"software phones" such as the product "NetMeeting".
6.2.9. The H.323 ALG Chapter 6. Security Mechanisms
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