IPV6 & failed scheduled backup

[AWS2P]

HI,

On windows pbxs on latest supported release, I noticed randomly on two different PBX , failed scheduled backup only on Windows PBXs, resolving IPV6 prior to IPV4 to resolve FTP location domain, in that case it's all the time an impossible access on FTP server and an undone backup.
I get this mail from pbx:
Your 3CX backup failed due to the following reason(s):
System.IO.IOException: Failed to connect to host.
at FluentFTP.FtpSocketStream.Connect(String host, Int32 port, FtpIpVersion ipVersions)
at FluentFTP.FtpClient.Connect(FtpSocketStream stream)
at FluentFTP.FtpClient.Connect()
at FluentFTP.FtpClient.Execute(String command)
at FluentFTP.FtpClient.DeleteFile(String path)
at _3cxFilesystemImplementations.FTP.FtpFilesystem.Delete(String filename)
at _3cxBackupRestoreImpl.BackupRestoreUtils.Backup(IFilesystem filesystem, String instanceId, String cfgPath, String dbConnectionString, BackupConfig options, String fullpathFilename, Boolean sendEmail)
at BackupRestoreSchedule.BackupJob.Execute(IJobExecutionContext context)

If I uncheck IPV6 in NIC properties to disable it, it works instantly.

What is the best way to handle this with IPV6 enabled ?
Thanks for advices

 

[ChrisC_3CX]

There should not be any issues when using IPV6, provided of course that IPV6 routing up the FTP server and back is possible. That said, you might want to check and confirm whether this is the case or not before re-enabling IPV6 on the 3CX PBX host.

 

[AWS2P]

In my mind for sure Public IPV6 to access FTP server is not NATED , only IPV4 is.
I try to add a rule and see what happens before re-enabling IPV6 on PBX.
This is weird since weeks it works fine and suddenly no more with same settings.

 

[AWS2P]

I've checked, my router is allowing incoming traffic on all IPs for FTP access , so I guess it include IPV6 adresses (even I'm not 100% sure)
If it is, so I don't have extra NAT rules to create.

 

[ChrisC_3CX]

You might want to consider running a packet capture on both the 3CX PBX and the FTP Server, have a scheduled backup start while both captures are running, wait for it to fail (receive the email) and then stop and review the packet captures to hopefully get a better idea of what is happening.

 

[AWS2P]

Well , i did some change in PBX registry to give priority answers to IPV4 , did some ping with FTP FQDN from PBX and first answer in windows was FTP public IPV4 adress, so now I just need to wait for next scheduled backup hoping it will run fine .

 

[ChrisC_3CX]

If you could avoid modifying registry entries by simply disabling IPV6 altogether I think that would be the way to go although this is of course up to you.

If you want to test it earlier, I guess you could just temporarily set the scheduled backup to run in the next 15 minutes.

 

[AWS2P]

I was following Microsoft advices here :
https://docs.microsoft.com/en-us/troubleshoot/windows-server/networking/configure-ipv6-in-windows
saying not to disable IPV6 but modify priority in DNS answer by changing Key value in registry, so i did and for now nslookup FQDN returns first IPV4, so like I said I will see real behavior with next scheduded update.

If you want to test it earlier, I guess you could just temporarily set the scheduled backup to run in the next 15 minutes.

You're right , i will if i need to see live what happens

 

[ChrisC_3CX]

Understood! Do let us know how it goes!