Round Robin DNS support for SFTP

[Viljami Kuosmanen]

There is currently a discrepancy in behaviour between using FTP and SFTP with servers using a Round Robin DNS configuration where a single domain lists multiple IP addresses in its type A or AAAA records.

With FTP, the Filezilla client will attempt to connect each listed IP address until finding a working one for the host, whereas with SFTP, Filezilla will only randomly try a single one and then fail immediately if that one fails.

The vanilla BSD sftp client on the command line will correctly try each IP address until finding a working one. This would be a desireable behaviour for the Filezilla client as well.

See screenshots below displaying different behaviours for FTP and SFTP on a host with round robin DNS configured. FTP tries all 3 hosts, while SFTP only tries to connect to one.

​https://seravo.fi/ftp-round-robin.png
​https://seravo.fi/sftp-round-robin.png

[Tim Kosse]

Same underlying cause as #10712