> Source: [sk143713](https://support.checkpoint.com/results/sk/sk143713)

# sk143713 - Inbound SIP calls experience one-way audio

| Property | Value |
|----------|-------|
| Solution ID | sk143713 |
| Date Created | 2019-01-07 |
| Last Modified | 2019-01-07 |
| Technical Level | Advanced |
| Products | Security Gateway |
| Versions | R82.10, R82, R81.20 |
| OS | Gaia |

## Symptoms

- * Inbound SIP calls experience one-way audio. (The issue does not affect outbound calls.)
* fw monitor outputs indicate that the SIP connection is NAT-ing properly.
* Kernel debugs include the following message (fw ctl debug -m fw + conn vm drop xlate xltrc nat tcpstr sip):   
  `sip_anticipate_conn: couldn't set kbuf in pending, free the kbuf;`

## Cause

The SDP payload in the SIP 200 OK packet did not change the recipient's RTP destination IP address to the cluster's External VIP when the IP header NATed properly. This caused the peer phone to send its audio packets to the incorrect IP address.

## Solution

This solution requires authentication. Please log in to view the full solution.

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