Mac Client Timeout: URL Resolving Not Working Properly

[twantzen]

Hello,

I’m working on two Macs (1st: OS X 10.12.6; 2nd: 10.13.6), but encounter problems with multiple FTP logins on the 1st one.

Most FTP-URLs do not resolve and I get the following errors in the log:

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08:41:40 Status:      	Verbinde mit xyz.de:23...
08:41:40 Antwort:    	fzSftp started, protocol_version=8
08:41:40 Befehl:      	open "USER@xyz.de" 23
08:42:40 Fehler:      	Zeitüberschreitung der Verbindung nach 60 Sekunden Inaktivität
08:42:40 Fehler:      	Herstellen der Verbindung zum Server fehlgeschlagen

Miraculously on CyberDuck the same connection on the same machine works perfectly. And on my second Mac even FileZilla works perfectly with the exakt same preferences and login parameters.

And if I change the FTP-URL to the corresponding IP adress, then everything works fine.

It seems, that I’m not alone with this problem (sorry – it’s German): https://youtu.be/edcf22QkDzU

Are there any ideas, what could cause this resolving issue?

Thanks in advance,
Tobias

[botg]

Port 23 is for Telnet. FileZilla does not speak Telnet.

[twantzen]

Thank you for your feedback, but Port 23 is the specification from the hosting provider. I also tried Port 21 without success, so there must be another reason, why URL resolving sometimes fails on Mac OS X.

Thanks,
Tobias

[botg]

The log does not show any indication of a URL resolving failure.

There simply does not appear to be a working SFTP server at xyz.de:23

[twantzen]

But if I use CyberDuck with the exact same configuration, it works perfectly.
Or if I use FileZilla with the IP adress instead of the named server, it works perfectly.

So there must be another reason, why this happens.

Tobias

[botg]

Does your system have a faulty IPv6 configuration? Some less advanced software products may not yet support IPv6.

[twantzen]

Does your system have a faulty IPv6 configuration? Some less advanced software products may not yet support IPv6

Thanks for your suggestion! I disabled v6 in terminal

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networksetup -setv6off Ethernet && networksetup -setv6off Wi-Fi

and now all server names are resolved correctly!

After turning it on again with

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networksetup -setv6automatic Wi-Fi && networksetup -setv6automatic Ethernet

I get the same error as before.

So you’re right – it must have something to do with the IPv6. Is there a config table or something else, which needs fixing? My other Mac runs perfectly with automatic IPv6 config. Do you have any idea, which is worth trying?

Thanks a lot!
Tobias

[botg]

They were resolved correctly beforehand as well. This has nothing to do with resolving.

[twantzen]

They were resolved correctly beforehand as well. This has nothing to do with resolving.

Okay, so I don’t understand, why. Would you mind, explaining the issue to me, what causes the error, if IPv6 is on?

Thanks,
Tobias

[botg]

The hostname resolves properly into an IP address. Which family of address depends on your networking setup. If your networking setup is wrong, your system resolves addresses, valid and correct addresses, it cannot use.

[boco]

It is not the resolving that's the issue. The IPv6 is resolved correctly, but it is blocked, somehow. Not working path MTU discovery, or a ghost route are possible causes.

[twantzen]

This gets too technical for me. I’m living with either IPv6 off or IP adresses instead of named servers in FileZilla.

Thank you very much for your efforts!
Tobias