Softphone doesn't work on over VPN - one way audio

[ligand]

Hello.
I'm having a problem with the softphone on my iphone when I'm traveling.  When I'm home and I use the softphone it works great with no issues.  However, when I'm traveling and VPN in (OpenVPN, OpenConnect, Wireguard, etc.) I can register the softphone and I can dial an extension; but I can't hear the people I'm calling but the people I'm calling can hear me.  I've checked my rules and I don't see anything could be causing the problem.

I ran tcpdumps on tests and found that on my LAN interface I see 2 way traffic to and from the PBX host and my VPN ip address.  However, on the VPN interface I only see traffic from my softphone to the PBX.  I don't see any traffic from the PBX to the softphone.  See below

PBX = 192.168.25.10
softphone = 192.168.26.2

LAN Interface TCP dump
13:26:44.284680 IP (tos 0xb8, ttl 64, id 0, offset 0, flags [DF], proto UDP (17), length 200)
    192.168.25.10.12842 > 192.168.26.2.51720: [udp sum ok] UDP, length 172
13:26:44.300427 IP (tos 0x0, ttl 63, id 22887, offset 0, flags [none], proto UDP (17), length 200)
    192.168.26.2.51720 > 192.168.25.10.12842: [udp sum ok] UDP, length 172
13:26:44.304683 IP (tos 0xb8, ttl 64, id 0, offset 0, flags [DF], proto UDP (17), length 200)
    192.168.25.10.12842 > 192.168.26.2.51720: [udp sum ok] UDP, length 172
13:26:44.324658 IP (tos 0xb8, ttl 64, id 0, offset 0, flags [DF], proto UDP (17), length 200)
    192.168.25.10.12842 > 192.168.26.2.51720: [udp sum ok] UDP, length 172
13:26:44.331735 IP (tos 0x0, ttl 63, id 42189, offset 0, flags [none], proto UDP (17), length 200)
    192.168.26.2.51720 > 192.168.25.10.12842: [udp sum ok] UDP, length 172
13:26:44.344750 IP (tos 0xb8, ttl 64, id 0, offset 0, flags [DF], proto UDP (17), length 200)
    192.168.25.10.12842 > 192.168.26.2.51720: [udp sum ok] UDP, length 172
13:26:44.347477 IP (tos 0x0, ttl 63, id 34116, offset 0, flags [none], proto UDP (17), length 200)
    192.168.26.2.51720 > 192.168.25.10.12842: [udp sum ok] UDP, length 172

Wireguard interface TCP Dump
13:26:44.213624 IP (tos 0x0, ttl 64, id 49427, offset 0, flags [none], proto UDP (17), length 200)
    192.168.26.2.51720 > 192.168.25.10.12842: [udp sum ok] UDP, length 172
13:26:44.224958 IP (tos 0x0, ttl 64, id 20234, offset 0, flags [none], proto UDP (17), length 200)
    192.168.26.2.51720 > 192.168.25.10.12842: [udp sum ok] UDP, length 172
13:26:44.244824 IP (tos 0x0, ttl 64, id 46429, offset 0, flags [none], proto UDP (17), length 200)
    192.168.26.2.51720 > 192.168.25.10.12842: [udp sum ok] UDP, length 172
13:26:44.244960 IP (tos 0x0, ttl 64, id 22431, offset 0, flags [none], proto UDP (17), length 200)
    192.168.26.2.51720 > 192.168.25.10.12842: [udp sum ok] UDP, length 172
13:26:44.256824 IP (tos 0x0, ttl 64, id 58053, offset 0, flags [none], proto UDP (17), length 200)
    192.168.26.2.51720 > 192.168.25.10.12842: [udp sum ok] UDP, length 172
13:26:44.276783 IP (tos 0x0, ttl 64, id 15971, offset 0, flags [none], proto UDP (17), length 200)
    192.168.26.2.51720 > 192.168.25.10.12842: [udp sum ok] UDP, length 172
13:26:44.300382 IP (tos 0x0, ttl 64, id 22887, offset 0, flags [none], proto UDP (17), length 200)
    192.168.26.2.51720 > 192.168.25.10.12842: [udp sum ok] UDP, length 172

I don't think its a NAT issue since everything is happening "internally" and I have set asterisk to consider 192.168.26.0/24 has a local network.

Any ideas/suggestions would be really helpful. 

Thanks in advance.

[ligand]

Hi Everyone,
I figured out the issue.  Basically I have 2 gateways on the firewall.  One is the standard gateway for my ISP.  The other is for a VPN that is used for certain types of traffic.  I ended up creating a rule in the LAN segment that directed traffic to my OpenVPN network through the OpenVPN server gateway.  Once that was done then I was able to have 2 way audio from my softphone while traveling.

Hope this helps

[AlvaradoSS]

From what you've described, it seems like a routing or firewall issue. Your TCP dumps show communication going one way, which might indicate that the traffic is getting blocked somewhere.
First, double-check your VPN settings and make sure it allows bidirectional traffic. Also, take a look at any firewalls along the route – they might be causing the audio to get lost. As you mentioned, your network configurations and Asterisk settings seem fine, so the culprit might be in the VPN setup.
If you're up for trying out a different softphone app, Acrobits has been known to handle such situations quite well. I suppose it can be a solution for you.