ALG can cause VOIP issues such as one-way or no audio speech path, call drops, unable to park/retrieve a call. There is a way to inspect a trace to spot ALG or SIP Transformation presence.
This is only applied to hard phone call traces. Web phones will always have the public ip in the sip header
What do I need?
- Hard phone call trace example (How to get the call trace sample? )
Inspecting a call trace for SIP ALG
INBOUND - In this example, an inbound call is terminated to the switch and the the call is routed to the client phone.
- In the call trace example, locate the SIP/2.0 200 OK response from the client public IP.
- If the value of Contact and c= IN IPV4 fields contain the public ip of the client then SIP ALG is turned on.
OUTBOUND - In this example, an outbound call is placed from a client's network hard phone to an external number
- Identify the call trace first invite to make sure it's coming from the client's public IP and click on it as pointed with a green arrow in the example below.
- If the value of Contact and c= IN IPV4 fields contain the public ip of the client then SIP ALG is turned on.