File backups fail when connected by ipv6

Server
#1

When a local client connects via IPv6 file backups fail:

ERROR  Error getting filelist of CLIENT. Errorcode: TIMEOUT (2)

In order to get it to run, I have to restart the client service a random number of times till it randomly decides it will use IPv4.

Would be helpful if the server had an option to simply disable IPv6 support, as I don’t use IPv6 for local connections & my ISP doesn’t support it for remote ones.

Took me quite a while to figure out what was going on & why one client suddenly stopped completing file backups (oddly image backups were working, which distracted me from looking at simple client/server connectivity issues).

Client File backup doesn't work on a Windows Server 2016, Image backup is OK
#2

Hello,

@Bearded_Blunder thanks for the analyses! I can confirm this issue in different installations.

The backup of the windows clients runs only sometimes or very delayed. I got error mails every time and the urbackup.log contains the error messages:

...
2020-09-01 08:47:55: ERROR: Incremental Backup of NBTerra-Rektor failed - CONNECT error -2
2020-09-01 08:48:01: ERROR: Backup had an early error. Deleting partial backup.
2020-09-01 08:48:02: WARNING: Exponential backoff: Waiting at least 40m before next file backup
2020-09-01 09:28:16: WARNING: Restarting shadow copy of C:\ because it was started by this server
2020-09-01 09:28:16: ERROR: Incremental Backup of NBTerra-Rektor failed - CONNECT error -2
2020-09-01 09:28:22: ERROR: Backup had an early error. Deleting partial backup.
2020-09-01 09:28:23: WARNING: Exponential backoff: Waiting at least 1h 20m before next file backup
2020-09-01 10:48:36: WARNING: Restarting shadow copy of C:\ because it was started by this server
2020-09-01 10:48:36: ERROR: Incremental Backup of NBTerra-Rektor failed - CONNECT error -2
2020-09-01 10:48:43: ERROR: Backup had an early error. Deleting partial backup.
2020-09-01 10:48:44: WARNING: Exponential backoff: Waiting at least 2h 40m before next file backup
...

As soon as i deactivate ipv6 on the urbackup linux host, the backup of the windows clients works smoothly.

@uroni @ Developers
Please take note of this report and maybe there is a possibility to find a fix.
Thanks for this great backup software!

Kind regards
Klaus

#3

I second this. Exactly the same problem here. It would be great to have a solution to this.

#4

Sorry you are having issues. To solve the problem the server (debug) log would be useful.
If possible, could you post it or send it?

This post describes how to change the server to debug logging, where it is stored and where to send it to if posting is not possible: Having problems with UrBackup? Please read before posting

Going further strace/procmon logs of the server/client processes would be helpful as well.

Thanks!

Disable IPv6 on sever?
#5

I’m getting this same issue.
Client Version: 2.4.10
Server Version: 2.4.13 Rev. 406665151b (on Windows Server 2019)

Server debug logs:
2020-12-27 13:16:00: ERROR: Getting Client settings of DCAD01 failed - CONNECT error
2020-12-27 13:16:00: ERROR: Getting client settings failed -2

I have 3 clients working (that are using IPv4) and 9 that are failing backups (both scheduled and on-demand).

No firewall issues, and they are all on the same subnet.

#6

@dmnet On my setup (Server 2012R2), since I don’t use IPv6 anyway, I worked around the issue by simply unchecking IPv6 in my network adapter properties on the server.

This sadly renders any debug logs I might have produced for @uroni before doing so moot only I’d done it already by the time he suggested obtaining them, but fixed backups.

#7

Thanks! Unfortunately that’s not an option as I’m enabling dual-stack shortly on this network.

#8

This seems to be resolved after running netsh interface ipv6 set prefixpolicy ::ffff:0:0/96 46 4

https://dimitri.janczak.net/2016/11/15/prefer-ipv4-ipv6-windows/#:~:text=To%20have%20IPv4%20favored%20over,old%20route%20utility%20under%20IPv4.