I am setting up a test configuration for a prospective client, who works in Finance, so everything has to have some redundancy. I can cope with most of their needs, but I'm not sure I'm taking the right path with regards their broadband, so please pitch in with comments/advice: They have 2 broadband lines, with 2 separate providers, one of the routers is a Draytek Vigor 2820 with GSM failover, the other router I'm not sure of the make, but it supports wan fail-over. The set up is right now: Router 1 - set with static IP's and the PBX would be using IP "1C" (router 1 Fixed IP 3rd in the range), ADSL is set to Wan failover to Router 2 incase of failure. Router 2 - Draytek 2820, again static IP's from ADSL provider, set to failover to GSM (dynamic IP - 1 only) in event of failure (typically to protect against cables being cut/local exchange issue). This setup is how their network was designed for maximum robustness within the price they wanted to spend. The 3CX system was only going to use 1 NIC, with the machine having 1 internal static IP. STUN was going to be disabled and use the static IP. (this is the prefered method if I understand correctly?) Router 1 would have open "VOIP" ports for the "1C" external address pointing to the internal static IP (just like you would with a single broadband connection). So far no issues. Router 2 for both the ADSL and GSM would have open "VOIP" ports hopefully pointing to the internal static IP of the 3CX box. However the 3CX box, if it suffers a Router 1 failure, will be sending outbound packets using the External static IP "1C" which if 9as they need to) are replied to will hit a "Dead" end. Is the solution as simple as enabling STUN and not using a static external IP? If the lines had been cut (they recently had builders/road works do just that) then the GSM backup would not offer a fixed IP in any event, unless a dynadns account was used. But I don't think 3CX could cope with 2 fixed IP's let alone 3! Or could the issue be resolved with using Dynadns to resolve to the 3CX box and not use STUN or a ADSL assigned static IP and use DynaDNS permanently? Has anyone configured something similar? The next question would be about load balancing/QoS, but 1 step at a time! I'll have a internal configuration on Monday to start testing/playing, but would rather avoid silly mistakes and take any help before I start that is out there. My recent BT Broadband experience will get posted, as it was a total mess, but finally resulted in an 11mb connection from an initially rated 5mb and after their 10 days of "settling in" a speed of only 60k - yes as slow as a modem! Anyway, another post... Thanks in advance.