after updating globus-ftp-client from v8.19 to v8.21 FTS3 transfers to IPv6-only site failed.
This was caused by the gridftp-transfers not being initiated in EPSV - which supports IPv6 - but falling back to passive mode PASV without IPv6 support. The behavior can be reproduced by up/downgrading the globus-ftp-client between v8.19 and v8.21.
Explicitly exporting globus parameters for enabling IPv6 in globus into the FTS environment, e.g.,
did not improve the behaviour.
Related tickets are
As of Globus 5.2.4, IPv6 can be enabled for Globus I/O by setting the GLOBUS_IO_IPV6 environment variable (to any value).
As of Globus 5.2.5, IPv6 can be enabled for Globus FTP as well by setting the GLOBUS_FTP_CLIENT_IPV6 environment variable (to any value).
More details in the following tickets.