SFTP and IPV6 [feature request] IPv4 Only option

[Gotta Getmedat]

Hi I wanted to explain my situation and recommend a solution.
I setup SFTP with a Synology NAS so it uses SSH ultimately. Typically port 22 but I am connecting remotely to said backup server in a consumer home connection so I have to use alternate port that's fine.
Routing through a couple not the greatest of routers is a bit tricky but works fine.

Basically the consumer home connection means it has to use DDNS (Dynamic DNS so the IP will randomly change) the NAS handles this perfectly no problems.

I have connected with a proxy on another computer to confirm everything works great via an external client connection origin (FFS to DDNS NAS over SFTP).

Alas in some more rare situations I have not totally determined the source of this problem. I think maybe it's an older mac OS (not too old mind you) or the provider on the other end. That it causes FFS trouble connecting.

What I did to confirm so far is using the OSX Terminal (unix bash shell) I could 'ping' the dynamically pointed domain name no problem, but 'telnet' fails until you put the "-4" (force IPv4 flag) command then it connects instantly.

Your software for "SFTP" needs an option to connect only with IPV4 or IPV6 I suppose if the user wants to limit that. I would assume it should try IPv6 and resort to IPv4 if IPv6 fails when the default of using 'Both' is selected.

Anyway maybe one can disable IPv6 usage in OSX somehow but it would be better to have this ability within FFS, thanks.

[Zenju]

Simplest solution is to configure your DDNS to return only IPv4. Better solution: find out why IPv6 doesn't work. Maybe a router firewall is blocking it, or IPv6 privacy extensions are interfering.

[Plerry]

Alternatively, you may consider to configure your Synology NAS as a VPN server, and connect to your NAS via CIFS/SMB via the encrypted VPN tunnel.
Or, if your NAS-side router can act as a VPN server, you can use that router's VPN server instead of your NAS.

[Gotta Getmedat]

Well the Synology DDNS is beyond my control and works fine for other routes so that's probably not the best solution. It could be redone through another provider like freedns.afraid.org I know and like, but I'm not sure about if you can turn off ipv6 there either.

The Tunnel is bad because all the traffic would be routed through the romote address and much hard to setup and be secure in some ways. I guess there's a way to route only that remote's local ip through the tunnel, still it's better to disable IPv6 on the Mac maybe I'm not sure. Gonna try that next I suppose, otherwise I can manually put the IP4 address but being Dynamic it will change randomly.

https://osxdaily.com/2014/04/18/disable-ipv6-mac-os-x/

Anyway it would be great to just have a checkbox or even automatic solution within FFS.

Thanks for the ideas.

[Gotta Getmedat]

Well you know I am not entirely sure that that is the problem now. I will come back if and when I figure out what is interfering with the connection.

I did try the IPv4 address directly and it still didn't like it, so it's unclear now. Also I checked with test-ipv6.com and the remote was all clear but the server says something odd about it working but the browser showing preference for ipv4 so I'm side tracking on that even though it worked via a free VPN through New York, etc. I am more convinced my home consumer grade provider's connection is the limiting factor. Be it intentional or because of incompetence I am left to ponder (but it can't be me?! ha ha).