R7000P V1.3.3.140_10.1.75 forward sip message , don't change ip.src

vccomnet wrote:

the Netgear R7000P router does not modify the value of the ip.src field of the UDP message when forwarding SIP (UDP). The specific situation is shown in the following picture:

I just looked at your diagram again.

The R7000p shouldn't be modifying that field.  The SBC is connected to a LAN port of the R7000p, so the NAT in the R7000p router isn't engaged.

To clarify the normal NAT behavior....

1. The SIP phone has 192.168.1.153 in its source address
2. The packet is sent upstream to the Huawei router
3. The Huawei router will change that source IP address to its WAN IP address (10.0.0.10) when it sends the packet upstream to the R7000p.

The R7000p isn't actually routing the packet to the SBC using layer-3 (IP).  The ethernet switch built into the router is sending it to the SBC using its MAC address table (layer 2).  The router software never sees the packet.

So look more closely at the Huawei router settings.

Also the upstream port on the Huawei router is labeled as LAN, not WAN.  I am guessing that is a mistake in the diagram.  If not, you need to change that connection to a WAN port.