# \[NAT Troubles\] - Two Asterisk PBXs behind the same public IP **URL:** \ **Category:** Asterisk General\ **Created:** [September 13, 2013, 2:37pm UTC](https://community.asterisk.org/t/nat-troubles-two-asterisk-pbxs-behind-the-same-public-ip/43904 "2013-09-13T14:37:27Z")\ **Posts on this page:** 2\ **Page:** 1
**Author:** ![system](https://global.discourse-cdn.com/asterisk/original/2X/4/475d0c889911cfb84ac4881ad6df8b523e3f9105.png) [@system](https://community.asterisk.org/u/system)\ **Post date:** [September 13, 2013, 2:37pm UTC](https://community.asterisk.org/t/nat-troubles-two-asterisk-pbxs-behind-the-same-public-ip/43904/1 "2013-09-13T14:37:27Z")
Hi everybody, I need your help to undersand how can I solve what, in my opinion, is a NAT problem. This is my configuration: VoIP Provider \<–\> Asterisk 11.5.x + A2Billing server \<–\> PBX A + PBX B (each one Asterisk 1.8.x) I can act without problems everywhere except on VoIP provider systems (I’ve to ask what I need and they say me if it’s possible or not…) PBX A and PBX B are on the same network behind the same firewall and the same router + public IP (I’ve only one public IP so I had to NAT my PBXs). THE PROBLEM: I’ve a SIP trunk open from the PBX A to the A2Billing server for a geographical number A and another trunk open (obviusly with different credentials) from the PBX B to the A2Billing server for a geographical number B. When I call number A from a cell phone, the call arrive to PBX A. When I call number B from a cell phone, the call still arrive to PBX A! And obviusly, here I don’t have an inbound route for that number… so the call fail and I ear ss-noservice audio file. If I launch netstat-nat -n on my firewall I see: `udp 192.168.1.7:5060 theIPofA2BillingServer:5060 ASSURED udp 192.168.1.9:5060 theIPofA2BillingServer:5060 ASSURED ` Some configurations… Some of my A2Billing VoIP settings are: qualify=yes type=friend host=dynamic nat=comedia canreinvite=yes Some of my PBX config : type=peer trustrpid=yes sendrpid=yes qualify=yes port=5060 nat=yes maxexpirey=3600 insecure=invite,port canreinvite=yes In my firewall iptables I have: -A PREROUTING -i eth0 -p udp -m multiport --dports 5060:5070 -j DNAT --to-destination 192.168.1.9 -A PREROUTING -i eth0 -p udp -m multiport --dports 10000:20000 -j DNAT --to-destination 192.168.1.9 -A FORWARD -d 192.168.1.9/32 -i eth0 -o eth1 -j fwd\_wanlan\_pbx -A fwd\_wanlan\_pbx -p udp -m multiport --dports 5060:5070 -j ACCEPT -A fwd\_wanlan\_pbx -p udp -m multiport --dports 10000:20000 -j ACCEPT where 192.168.1.9 is PBX A. Do you think I need some modify for PBX B (192.168.1.7)? How do you think I can solve this problem? Thank you so much! ---
**Author:** ![abw1oim](https://avatars.discourse-cdn.com/v4/letter/a/8e7dd6/32.png) [@abw1oim](https://community.asterisk.org/u/abw1oim)\ **Post date:** [September 17, 2013, 4:45pm UTC](https://community.asterisk.org/t/nat-troubles-two-asterisk-pbxs-behind-the-same-public-ip/43904/2 "2013-09-17T16:45:11Z")
You need to distinct the signalling (SIP) as well as the RTP ports used ny the Asterisk-servers behind the same IP-Adress. Your firewall actully delivers all SIP/RTP-traffic to server A. to avoid this, change server B e.g to bindport 5062 and set up the rtp-range in Server A to start 10000 and stop 15000 as well as on server B from 15001 to 20000. Afterwards Your firewall config may look like ```auto -A PREROUTING -i eth0 -p udp -m multiport --dports 5060:5061 -j DNAT --to-destination 192.168.1.9 -A PREROUTING -i eth0 -p udp -m multiport --dports 10000:15000 -j DNAT --to-destination 192.168.1.9 -A FORWARD -d 192.168.1.9/32 -i eth0 -o eth1 -j fwd_wanlan_pbx -A PREROUTING -i eth0 -p udp -m multiport --dports 5062:5063 -j DNAT --to-destination 192.168.1.7 -A PREROUTING -i eth0 -p udp -m multiport --dports 15001:20000 -j DNAT --to-destination 192.168.1.7 -A FORWARD -d 192.168.1.7/32 -i eth0 -o eth1 -j fwd_wanlan_pbx -A fwd_wanlan_pbx -p udp -m multiport --dports 5060:5063 -j ACCEPT -A fwd_wanlan_pbx -p udp -m multiport --dports 10000:20000 -j ACCEPT ```