Hello there!

Problem was solved.

These two iptables lines helped me out:

iptables -t nat -A PREROUTING -i eth2 -p udp -m udp --dport 8100:8200 -j DNAT --to-destination 192.168.3.250

iptables -t nat -A PREROUTING -i eth2 -p udp -m udp --dport 5060 -j DNAT --to-destination 192.168.3.250

where 8100:8200 is my RTP port range, and 5060 is my SIP port.

Do you have a place to define the subnets within the PBX? You may not have both subnets defined, its possible the pbx is doing some type of NAT traversal on local subnets, which shouldn't be needed.

I am curious: what software are you using?

Hi Nick

I will check this tomorrow at work, but tricky thing is that the softphones working well in every subnet.

Are you able to check if there are any multicast packets coming from your PBX? perhaps monitor traffic on your LAN2 interface from your PBX IP to destinations in the range 224.0.0.0 to about 233.255.255.255 (a bit of a sledgehammer but it should work). Also do the same for an IP phone on LAN2. If there is any then you may gave an issue as multicast does not travel between LAN subnets. You'll need a special set up for that to work. Google something like "subnet multicast linux" for more information. Or, perhaps your PBX can be configured differently; I don't know anything about them.