Voice traffic on NAT

[zheepern0826]

Hi guys, 

I have 2 sites and they are using MPLS to connect to each other. 

CUCM server is in Site A and end user sit in Site B. 

I have allow the traffic on firewall rules and end user windows jabber able to login and make call. However, when they calling, they can't hear the voice but the called party can hear them. 

I tried to check on the NAT and notice when we are using one to one NAT, voice can go through and we can hear each other. When they using many to one NAT, users cannot hear but called party can hear. 

Below is the connection: 

Site B user private IP -> NAT to 10.30.1.2 -> MPLS -> Site A network

Would like to check what should i do on the router to let it work ? 

Need your advise. Thank you very much in advance. 

[R0g22]

Who is doing NAT ? Firewall/GW/Router ?

[zheepern0826]

Hi Nipun, 

The NAT is on their Fortinet Firewall. 

Please advise how to proceed next. Thank you.

[R0g22 · Accepted solution]

Don't have experience with how Fortinet has it's NAT config but the most SIP/RTP friendly NAT is a Full Cone or Endpoint independent mapping per RFC 4787. Having said that, can you grab a pcap from the firewall egress to see what is happening. The UDP port information in the SDP would need to be a public live internet facing IP. The port is usually re-written by NAT devices as well.
For comparison, grab the pcap for a one to one map as well so that we can see the difference.