Network traffic flow between CDN servers behind NAT

A signaling and media network traffic flows directly between CDN servers. The network interfaces to use will be chosen as follows if CDN servers are behind NAT:

1. If Origin and Edge nodes are in the same private network/VPC (or in the same cloud region and datacenter), and the Origin private address is set in Edge parameters, for example

# Edge external address
ip = 192.168.1.31
# Edge private address
ip_local = 172.16.0.31
...
cdn_ip = 172.16.0.31
cdn_role = edge
# Origin private address
cdn_point_of_entry = 172.16.0.1

then signaling traffic will flow via private network.

2. If Origin and Edge nodes are in the same private network/VPC (or in the same cloud region and datacenter), and private address is allowed to use in SDP candidates both on Origin and Edge

rtc_ice_add_local_interface=true

then medai traffic will flow via private network, but a service packets like Receiver Report  and Sender Report will go through external network because external address is always the first in candidates list for publishing and playback in browsers to work correctly.

3. In all the other cases signaling and media traffic will flow via external network