One way audio for VoIP when using NAT in NSX

Products

• VMware NSX

Issue/Introduction

You may experience one way audio issues with VoIP calls when NAT is used in an NSX environment.

This issue may be intermittent.

Environment

VMware NSX

Cause

NAT can be used in several ways.  If using standard NAT in a 1:many (overload) configuration, the system defaults to PAT (port address translation) in which both IP and PORT are translated to a different value.  This also occurs with 1:1 NAT in NSX.

VoIP uses negotiated ports, and if the source is translated to a different port value the audio will fail.

Resolution

Set the NAT type to Reflexive.  This type of NAT does not hold state and does not translate ports as described in the NSX documentation for Network Address Translation.

Additional Information

If you've set your NAT type to Reflexive and still have issues, please open a case with Broadcom for further support.