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

Hi StephenB，

     Thank you for your reply. You are right, the WAN port of Huawei is connected to the LAN port of R7000P, and the markings in my picture are incorrect.

     Additionally, I understand what you're saying. The R7000P forwards packets from one LAN port to another, which is a function of a layer 2 switch and does not trigger routing or NAT processing. Binding a Polycom SIP phone to port 5060 and a non 5060 port yields different results. This is because Huawei routers have processed SIP ALG, meaning that they have not modified the ip.src. Therefore, when the message reaches SBC, the ip.src remains at 192.168.1.153 When SBC responds to SIP REGSITER requests, it will first send to the gateway (192.168.0.1). R7000P does not know where 192.168.1. x is located, so as long as a static route 192.168.1.0/24 to 192.168.0.10 is configured on R7000P, which is a Huawei router, I followed this method and the problem was solved.

Is my analysis correct? If there are any issues, please help point them out.

Finally, thank you for your professional answer.

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.

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:

Try going into the advanced WAN settings and disabling the SIP ALG.  See page 49 here:

• https://www.downloads.netgear.com/files/GDC/R7000P/R7000P_UM_EN.pdf