My recent experiences with ftp.ietf.org:
EPSV doesn't work - it gives a port which it then isn't listening on
(or, more likely since we get no response at all, a firewall blocks
229 Entering Extended Passive Mode (|||42065|)
ftp: connect for data channel: Operation timed out
[simultaneously in another window]
compost% telnet ftp.ietf.org 42065
telnet: connect to address 220.127.116.11: Operation timed out
EPRT for IPv4 doesn't work - it returns an error "Bad EPRT protocol."
---> EPRT |1|18.104.22.168|56318|
500 Bad EPRT protocol.
Apparently, the FTP server doesn't want to allow EPRT with IPv4.
("1" is IPv4). It's not using the 522 "I don't support that protocol"
error code, but is also saying that it doesn't support that
PORT doesn't work - it returns an immediate error "Failed to establish
---> PORT 192,20,225,40,219,254
200 PORT command successful. Consider using PASV.
425 Failed to establish connection.
tcpdump shows that it didn't send any packets trying to establish
a connection to 22.214.171.124 and the 425 error comes too
quickly to have tried.
It looks like 3 out of 4 data channel establishment mechanisms
are broken with this FTP server software and configuration for
IPv4. I didn't test with IPv6.
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