Understanding SIP ALG Unknown Message Types

This feature enables you to specify how unidentified Session Initiation Protocol (SIP) messages are handled by the device. The default is to drop unknown (unsupported) messages.

We do not recommend permitting unknown messages because they can compromise security. However, in a secure test or production environment, this command can be useful for resolving interoperability issues with disparate vendor equipment. Permitting unknown SIP messages can help you get your network operational so you can later analyze your voice-over-IP (VoIP) traffic to determine why some messages were being dropped. The unknown SIP message type feature enables you to configure the device to accept SIP traffic containing unknown message types in both Network Address Translation (NAT) mode and route mode.

Note: This option applies only to received packets identified as supported VoIP packets. If a packet cannot be identified, it is always dropped. If a packet is identified as a supported protocol and you have configured the device to permit unknown message types, the message is forwarded without processing.

Understanding SIP ALG Unknown Message Types

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