> Source: [sk184161](https://support.checkpoint.com/results/sk/sk184161)

# sk184161 - NAT IP address is not seen in the SIP Payload

| Property | Value |
|----------|-------|
| Solution ID | sk184161 |
| Date Created | 2025-10-16 |
| Last Modified | 2025-10-20 |
| Technical Level | General |
| Products | Security Gateway |
| Versions | R81.20, R81.10 (EOS) |
| OS | Gaia |
| Platform | Azure |

## Symptoms

- * When using software-based phone application (like Microsoft Teams, Zoom Phone and such), SIP calls are established successfully, but subsequent media transfer fails from the SIP client to the SBC (Session Border Controller).
* The NAT IP address is not reflected in the SIP payload (SDP body), only the private IP address appears.

## Cause

In an external-to-internal topology with proxy configuration, a code limitation prevents source IP NAT from being applied. As a result, when the internal host sends a "SIP 200 OK" response, NAT is not performed on the packet or the SDP (Session Description Protocol) payload, causing the media transfer to fail.

## Solution

[Contact Check Point Support](https://www.checkpoint.com/support-services/contact-support/) to get a Hotfix for this issue.

A Support Engineer will make sure the Hotfix is compatible with your environment before providing it.  
For faster resolution and verification, collect these files:

1. [CPinfo](https://support.checkpoint.com/results/sk/sk92739) file from the Management Server involved in the case.
2. [CPinfo](https://support.checkpoint.com/results/sk/sk92739) file from the Security Gateway / each Cluster Member / Security Group involved in the case.

**Hotfix installation instructions:**   
Refer to [sk168597 - How to install a Hotfix](https://support.checkpoint.com/results/sk/sk168597).

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