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With an IP phone that uses the VPN 3002 Client, the user experiences one-way audio during a conversation


Core Issue

The VPN 3002 Hardware Client may be configured to work in Port Address Translation (PAT) mode.


VPN 3002 is capable of operating in two modes: Client mode and NEM (Network Extension Mode). In Client mode, all the hosts earlier than the 3002 are in PAT mode to the outside IP address of the 3002. However, PAT breaks H.323. H.323 does not work with PAT.

When the VPN 3002 works in NEM, the remote networks    are capable of seeing each other using their real IP addresses, not a NAT or PAT IP address. If the VPN 3002 works in NEM, then H.323 works.

IP phones earlier than a 3002 work only in NEM.

To configure the VPN to work in NEM, perform these steps:

  1. Select Configuration > Quick > PAT.
  2. Choose No, use Network Extension mode from the PAT window to configure NEM.

For more information on configuring Cisco VPN 3002 Hardware Client, refer to Configuring Cisco VPN 3002 Hardware Client to Cisco IOS Router with EzVPN in Network Extension Mode.

For related information on one-way voice issues, refer to Troubleshooting One Way Voice Issues.

Problem Type

Call connection  (Connection quality: One-way audio, no busy tone, dropped calls, etc.)

IP phones and other clients  (Client registration, faulty IP phone, etc.)

Call Connection

One-way audio

IP Phones and Clients

IP phone faulty operation

Common Software and Product Issues


Failure Type

Cannot connect to server, disconnect, register, synchronize, communicate, etc.

Cannot perform routine, step, function, etc.

Frequency and Scope of Symptom

Only occurs in one direction

When Problem Occurs

During conversation

End Where Problem is Heard or Device Type Involved

IP phone

Call Topology and Direction

IP network > IP network

IP network > PSTN/PBX/gateway > IP network

Security Features

Virtual Private Network (VPN)