Solving SIP One-Way Audio Issues

• Source NAT policy configured to translate traffic from the mobile gateway to outside the Internet
• Source Address Translation Type set to ‘Dynamic IP And Port’

GUI: Policies > Nat > Add (or select configured policy)

• One-way audio issue when calling from third party softphone application to corporate mobile phones
• Only one UDP traffic flow between mobile gateway and the third party softphone application
• The firewall also translates the source port as shown below in packet captures.

• The responding UDP traffic flow is sent to the original source port, not the translated port due to SIP negotiation
• The firewall drops the responding UDP traffic flow

(drop stage pcap)

• Palo Alto 3220 Firewall
• PANOS 9.1.10
• Source NAT policy configured with 'Dynamic IP And Port' as Source Address Translation Type
• Third-party softphone application
• SIP (Session Initiation Protocol)

1. Modify the Source Address Translation Type from ‘Dynamic IP And Port’ to ‘Dynamic IP’ to solve the issue and have two-way audio flows:

(received and transmit stages merged pcap)


 

Source NAT Translation Types and Typical Use Cases