How use Dynamic Public IP with multiple Internet connections?

[uptime1]

This question pertains to a self-hosted Windows 3CX Server that's NAT'd behind a firewall:

If our primary Internet connection fails, our firewall will automatically failover to our secondary Internet connection which has a different set of public IP addresses, and the firewall will automatically update the IP address of the FQDN that 3CX clients and SBC's use to access the 3CX Server. And, our VOIP trunk provider is already configured for the secondary Internet connection.

1) Therefore, should we select Dynamic Public IP (IP changes) in Settings, Network, External IP Configuration?
2) How fast will the self-hosted (on premise, not cloud) Windows 3CX server recognize the changed Public IP address?

Our external devices are SBC's, Grandstream GXP2160 desktop phones through SBC's, 3CX smartphone apps, and maybe in the future, 3CX browser web client and/or 3CX Windows desktop client program. We don't use STUN, and never intent to.

3) Since all of the external devices are configured to reach the 3CX server via a FQDN, does it really matter to the 3CX server (NAT'd behind a firewall) that the Public IP address it uses to reach the Internet has changed? Would it even know?

Thanks!

 

[SteveITS]

An Enterprise license has a 5 minute TTL on a 3CX FQDN. Other editions are 6 hours.

The issues are around dropping active calls, the SIP provider being able to initiate a call, remote phones/apps/SBCs not able to connect until the IP updates, etc. If those are concerns and Enterprise isn't a fast enough TTL there are SD-WAN services to assign a public IP independent of ISP connections.

As for setting to dynamic, I believe that's correct, see https://www.3cx.com/community/threads/change-wan-ip.60345/

 

[uptime1]

Thanks. I'm not too concerned about dropping phones calls. I've custom created RPi SBC's that fail over to a cellular connection in 15 seconds, so I'm expecting the SBC will handle reconnecting quickly too. Impressively, the SBC fails back to the primary Internet connection seamless. The handoff happens without dropping audio!

I'll setup a test environment to thoroughly test this scenario. Should be interesting.

 

[ChrisC_3CX]

1) Therefore, should we select Dynamic Public IP (IP changes) in Settings, Network, External IP Configuration?

Yes you should. That way the PBX will every now and then use our STUN servers to discover what that IP is.

2) How fast will the self-hosted (on premise, not cloud) Windows 3CX server recognize the changed Public IP address?

That depends on when the next STUN query occurs. You can actually adjust the interval time in "Settings >> Network >> Public IP":


Note: What @SteveITS mentioned is for DNS resolution which to happen, means that the Host must learn of the new IP first. Provided of course you're using a 3CX FQDN.

3) Since all of the external devices are configured to reach the 3CX server via a FQDN, does it really matter to the 3CX server (NAT'd behind a firewall) that the Public IP address it uses to reach the Internet has changed? Would it even know?

Yes it does, first of all it has to update the DNS Record and it would need to know the new IP to do that(if using 3CX FQDN). Also, the public IP is used in SIP headers so the PBX has to know the ip if it is to construct those SIP messages correctly.

 

[uptime1]

Yes you should. That way the PBX will every now and then use our STUN servers to discover what that IP is.


That depends on when the next STUN query occurs. You can actually adjust the interval time in "Settings >> Network >> Public IP":
View attachment 29955

Note: What @SteveITS mentioned is for DNS resolution which to happen, means that the Host must learn of the new IP first. Provided of course you're using a 3CX FQDN.


Yes it does, first of all it has to update the DNS Record and it would need to know the new IP to do that(if using 3CX FQDN). Also, the public IP is used in SIP headers so the PBX has to know the ip if it is to construct those SIP messages correctly.

Thanks, ChrisC!

For a self-hosted on-premise 3CX Server not using a 3CX FQDN (or any STUN connected devices), is it still necessary for the 3CX Server to query the 3CX STUN server to determine the 3CX Server's public IP address?

Any issue with making the STUN query interval 30 or 60 seconds?

 

[uptime1]

Yes you should. That way the PBX will every now and then use our STUN servers to discover what that IP is.


That depends on when the next STUN query occurs. You can actually adjust the interval time in "Settings >> Network >> Public IP":
View attachment 29955

Note: What @SteveITS mentioned is for DNS resolution which to happen, means that the Host must learn of the new IP first. Provided of course you're using a 3CX FQDN.


Yes it does, first of all it has to update the DNS Record and it would need to know the new IP to do that(if using 3CX FQDN). Also, the public IP is used in SIP headers so the PBX has to know the ip if it is to construct those SIP messages correctly.

On another note, re: Network Settings, Firewall, Enable Keep Alives, does that apply to both SIP and RTP traffic?

And, where is the complete, extensive 3CX admin manual, preferably downloadable, for these deep subjects and questions? I looked all over the web site, Couldn't find a thing.

 

[ChrisC_3CX]

On another note, re: Network Settings, Firewall, Enable Keep Alives, does that apply to both SIP and RTP traffic?

It's basically just udp traffic sent every so many seconds to the SIP Provider.

And, where is the complete, extensive 3CX admin manual, preferably downloadable, for these deep subjects and questions? I looked all over the web site, Couldn't find a thing.

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