No VoIP traffic incoming

[vinz3nt]

Help! I hope anyone can help!

I have a hp msr20-21 router. Connected to WAN port 0/0 is a bridged modem with 1 ethernet port with a 255.255.255.248 subnet mask so effectively there are 6 IP addresses we are able to use where 1 is used for the gateway, in this case the 1 port bridget modem (without any firewall or something like that)

I am given the 2nd address which is to be used for internet traffic AND a SIP trunk. The other 4 public IP addresses are in use by the customer for Citrix, VPN and internet traffic. Everything is connected via a 8 port unmanaged hp switch so WAN port 0/0 is also connected to that switch. NAT is active. Multiple VLANs are active and routed through the LAN ports of the MSR20-21 to a core switch. All this is up and running and I really don't want to touch this again as there are already many Wifi stations (Ubiquiti) and Private GSM basestations active as wel as 50 IP clients (it's a care system for elderly people)

Well, internet traffic is working. The SIP trunk is configured on a software based VoIP PBX (Asterisk, FreePBX). Outgoing calls are working fine, SIP trunk uses UDP port 5060 for  registering and this works wihout any problem and without any change in de MSR20-21. Incoming calls though are not coming trough!

I monitored via the Asterisk CLI and Wireshark and I can clearly see there isn't any traffic coming in on the router, not 1 bit!

So first I forwarded UDP 5060 directly to the Asterisk server (via NAT configuration >> Internal Server. As soon as I save this the SIP trunk will disconnect and there's no way to get it up but removing the fowarding.

What DOES work is instead of only forwarding 5060, putting 0 for the port which will forward ALL UDP ports, after saving it stil doesn't work BUT, after a reboot of the router (which I really don't like) it works like a charm! In- and outgoing calls work flawlessly. But I really don't want to open all 65000 ports on a public IP address.

Sadly, trying with an old Cisco Linksys WRT120N router I use for testing will work in 2 minutes, I forward UDP 5060 and a range of 10000-100020 for RTP traffic, I press save and it works instantly, internet and incoming and outging calls so the problem (challenge) is in the MSR20-21.

I suspect I have to forward this 10000-100020 range but there's no option for that in the web gui, it even won't accept a 2nd entry for the same IP address (in this case the Asterisk server)

So.....anyone? I'm at the end of my knowledge as are my colleagues so I'm hoping on someone in the community!

Any help much appreciated!!!