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[quote="Gunni"]I just had a case where an FTP server i was trying to use, had an incorrect response to the [m]PASV[/m] command, causing connections to it to fail.

Obviously the server _should_ be configured right, but it's not mine… What to do…

I found [m]EPSV[/m], a feature _meant_ for IPv6, apparently, that works for this server, instant connection, instant directory listing, and 60ish MB/s for a 20GB file, no proooooblem…

Ok, a bit of a problem, no ftp client except lftp allow you to force use of [m]EPSV[/m] over IPv4…

FileZilla bug: https://trac.filezilla-project.org/ticket/10301 -- over 10 year old… no comments…

I found literally no posts on this in regards to WinSCP.

p.s. Obviously I prefer encrypted connections, but, again, not my server.

redacted TCPDump output:
(tcpdump was running on router between client and server, no encryption possible with server)
[code]
# tcpdump -pnni eth6 'host example.com'

16:26:16.683810 IP 192.0.2.1.21 > 198.51.100.1.60544: Flags [P.], seq 424:439, ack 92, win 8195, options [nop,nop,TS val 3435580973 ecr 2892720621], length 15: FTP: 230 Logged on
16:26:16.683992 IP 198.51.100.1.60544 > 192.0.2.1.21: Flags [P.], seq 92:97, ack 439, win 501, options [nop,nop,TS val 2892720624 ecr 3435580973], length 5: FTP: PWD
16:26:16.686152 IP 192.0.2.1.21 > 198.51.100.1.60544: Flags [P.], seq 439:470, ack 97, win 8195, options [nop,nop,TS val 3435580973 ecr 2892720624], length 31: FTP: 257 "/" is current directory.
16:26:16.686494 IP 198.51.100.1.60544 > 192.0.2.1.21: Flags [P.], seq 97:103, ack 470, win 501, options [nop,nop,TS val 2892720626 ecr 3435580973], length 6: FTP: PASV
16:26:16.689652 IP 192.0.2.1.21 > 198.51.100.1.60544: Flags [P.], seq 470:521, ack 103, win 8195, options [nop,nop,TS val 3435580979 ecr 2892720626], length 51: FTP: 227 Entering Passive Mode (203,0,113,1,216,229)
16:26:16.730890 IP 198.51.100.1.60544 > 192.0.2.1.21: Flags [.], ack 521, win 501, options [nop,nop,TS val 2892720671 ecr 3435580979], length 0
16:28:17.231490 IP 192.0.2.1.21 > 198.51.100.1.60544: Flags [P.], seq 521:548, ack 103, win 8195, options [nop,nop,TS val 3435701524 ecr 2892720671], length 27: FTP: 421 Connection timed out.
16:28:17.231490 IP 192.0.2.1.21 > 198.51.100.1.60544: Flags [F.], seq 548, ack 103, win 8195, options [nop,nop,TS val 3435701524 ecr 2892720671], length 0
16:28:17.231743 IP 198.51.100.1.60544 > 192.0.2.1.21: Flags [.], ack 548, win 501, options [nop,nop,TS val 2892841172 ecr 3435701524], length 0
16:28:17.231931 IP 198.51.100.1.60544 > 192.0.2.1.21: Flags [F.], seq 103, ack 549, win 501, options [nop,nop,TS val 2892841172 ecr 3435701524], length 0
16:28:17.235511 IP 192.0.2.1.21 > 198.51.100.1.60544: Flags [.], ack 104, win 8195, options [nop,nop,TS val 3435701528 ecr 2892841172], length 0
[/code]
vs
[code]
16:49:40.696171 IP 192.0.2.1.21 > 198.51.100.1.43250: Flags [P.], seq 424:439, ack 92, win 8195, options [nop,nop,TS val 3436985024 ecr 2894124634], length 15: FTP: 230 Logged on
16:49:40.696667 IP 198.51.100.1.43250 > 192.0.2.1.21: Flags [P.], seq 92:97, ack 439, win 501, options [nop,nop,TS val 2894124637 ecr 3436985024], length 5: FTP: PWD
16:49:40.698676 IP 192.0.2.1.21 > 198.51.100.1.43250: Flags [P.], seq 439:470, ack 97, win 8195, options [nop,nop,TS val 3436985024 ecr 2894124637], length 31: FTP: 257 "/" is current directory.
16:49:40.699283 IP 198.51.100.1.43250 > 192.0.2.1.21: Flags [P.], seq 97:103, ack 470, win 501, options [nop,nop,TS val 2894124639 ecr 3436985024], length 6: FTP: EPSV
16:49:40.701861 IP 192.0.2.1.21 > 198.51.100.1.43250: Flags [P.], seq 470:518, ack 103, win 8195, options [nop,nop,TS val 3436985029 ecr 2894124639], length 48: FTP: 229 Entering Extended Passive Mode (|||55302|)
16:49:40.702370 IP 198.51.100.1.45294 > 192.0.2.1.55302: Flags [S], seq 955069495, win 64240, options [mss 1460,sackOK,TS val 2894124643 ecr 0,nop,wscale 7], length 0
16:49:40.704474 IP 192.0.2.1.55302 > 198.51.100.1.45294: Flags [S.], seq 2225977054, ack 955069496, win 65535, options [mss 1460,nop,wscale 8,sackOK,TS val 3436985032 ecr 2894124643], length 0
16:49:40.705007 IP 198.51.100.1.45294 > 192.0.2.1.55302: Flags [.], ack 1, win 502, options [nop,nop,TS val 2894124645 ecr 3436985032], length 0
16:49:40.705059 IP 198.51.100.1.43250 > 192.0.2.1.21: Flags [P.], seq 103:109, ack 518, win 501, options [nop,nop,TS val 2894124645 ecr 3436985029], length 6: FTP: LIST
16:49:40.708460 IP 192.0.2.1.21 > 198.51.100.1.43250: Flags [P.], seq 518:573, ack 109, win 8195, options [nop,nop,TS val 3436985036 ecr 2894124645], length 55: FTP: 150 Opening data channel for directory listing of "/"
16:49:40.708618 IP 192.0.2.1.55302 > 198.51.100.1.45294: Flags [P.], seq 1:148, ack 1, win 8195, options [nop,nop,TS val 3436985036 ecr 2894124645], length 147
16:49:40.708618 IP 192.0.2.1.55302 > 198.51.100.1.45294: Flags [F.], seq 148, ack 1, win 8195, options [nop,nop,TS val 3436985036 ecr 2894124645], length 0
16:49:40.708904 IP 198.51.100.1.45294 > 192.0.2.1.55302: Flags [.], ack 148, win 501, options [nop,nop,TS val 2894124649 ecr 3436985036], length 0
16:49:40.708929 IP 198.51.100.1.45294 > 192.0.2.1.55302: Flags [F.], seq 1, ack 149, win 501, options [nop,nop,TS val 2894124649 ecr 3436985036], length 0
16:49:40.709585 IP 192.0.2.1.21 > 198.51.100.1.43250: Flags [P.], seq 573:607, ack 109, win 8195, options [nop,nop,TS val 3436985037 ecr 2894124645], length 34: FTP: 226 Successfully transferred "/" 
[/code][/quote]

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Topic review

Gunni

Re: Allow forcing and or fallback to use of EPSV over IPv4

2025-08-18 14:15

Unable, I do not have access to that server anymore.

By the way I suspect that the cause is FTP conntrack allowing connections to the wrong IP and therefore not allowing this connection.

martin

Re: Allow forcing and or fallback to use of EPSV over IPv4

2025-08-18

Please post a log for that.

Gunni

Re: Allow forcing and or fallback to use of EPSV over IPv4

2025-08-18 14:02

I did, I tried every option On and Off, no change.

I _suspect_ the cause is that any router in between that has the FTP conntrack module, it's going to allow connectivity to the wrong IP provided by the server in the PASV response.

martin

Re: Allow forcing and or fallback to use of EPSV over IPv4

2025-08-18

Please try enabling "Force IP address for passive mode connections":
https://winscp.net/eng/docs/ui_login_ftp

Gunni

Allow forcing and or fallback to use of EPSV over IPv4

2025-08-17 18:52

I just had a case where an FTP server i was trying to use, had an incorrect response to the PASV command, causing connections to it to fail.

Obviously the server _should_ be configured right, but it's not mine… What to do…

I found EPSV, a feature _meant_ for IPv6, apparently, that works for this server, instant connection, instant directory listing, and 60ish MB/s for a 20GB file, no proooooblem…

Ok, a bit of a problem, no ftp client except lftp allow you to force use of EPSV over IPv4…

FileZilla bug: https://trac.filezilla-project.org/ticket/10301 -- over 10 year old… no comments…

I found literally no posts on this in regards to WinSCP.

p.s. Obviously I prefer encrypted connections, but, again, not my server.

redacted TCPDump output:
(tcpdump was running on router between client and server, no encryption possible with server)

# tcpdump -pnni eth6 'host example.com'



16:26:16.683810 IP 192.0.2.1.21 > 198.51.100.1.60544: Flags [P.], seq 424:439, ack 92, win 8195, options [nop,nop,TS val 3435580973 ecr 2892720621], length 15: FTP: 230 Logged on

16:26:16.683992 IP 198.51.100.1.60544 > 192.0.2.1.21: Flags [P.], seq 92:97, ack 439, win 501, options [nop,nop,TS val 2892720624 ecr 3435580973], length 5: FTP: PWD

16:26:16.686152 IP 192.0.2.1.21 > 198.51.100.1.60544: Flags [P.], seq 439:470, ack 97, win 8195, options [nop,nop,TS val 3435580973 ecr 2892720624], length 31: FTP: 257 "/" is current directory.

16:26:16.686494 IP 198.51.100.1.60544 > 192.0.2.1.21: Flags [P.], seq 97:103, ack 470, win 501, options [nop,nop,TS val 2892720626 ecr 3435580973], length 6: FTP: PASV

16:26:16.689652 IP 192.0.2.1.21 > 198.51.100.1.60544: Flags [P.], seq 470:521, ack 103, win 8195, options [nop,nop,TS val 3435580979 ecr 2892720626], length 51: FTP: 227 Entering Passive Mode (203,0,113,1,216,229)

16:26:16.730890 IP 198.51.100.1.60544 > 192.0.2.1.21: Flags [.], ack 521, win 501, options [nop,nop,TS val 2892720671 ecr 3435580979], length 0

16:28:17.231490 IP 192.0.2.1.21 > 198.51.100.1.60544: Flags [P.], seq 521:548, ack 103, win 8195, options [nop,nop,TS val 3435701524 ecr 2892720671], length 27: FTP: 421 Connection timed out.

16:28:17.231490 IP 192.0.2.1.21 > 198.51.100.1.60544: Flags [F.], seq 548, ack 103, win 8195, options [nop,nop,TS val 3435701524 ecr 2892720671], length 0

16:28:17.231743 IP 198.51.100.1.60544 > 192.0.2.1.21: Flags [.], ack 548, win 501, options [nop,nop,TS val 2892841172 ecr 3435701524], length 0

16:28:17.231931 IP 198.51.100.1.60544 > 192.0.2.1.21: Flags [F.], seq 103, ack 549, win 501, options [nop,nop,TS val 2892841172 ecr 3435701524], length 0

16:28:17.235511 IP 192.0.2.1.21 > 198.51.100.1.60544: Flags [.], ack 104, win 8195, options [nop,nop,TS val 3435701528 ecr 2892841172], length 0

16:49:40.696171 IP 192.0.2.1.21 > 198.51.100.1.43250: Flags [P.], seq 424:439, ack 92, win 8195, options [nop,nop,TS val 3436985024 ecr 2894124634], length 15: FTP: 230 Logged on

16:49:40.696667 IP 198.51.100.1.43250 > 192.0.2.1.21: Flags [P.], seq 92:97, ack 439, win 501, options [nop,nop,TS val 2894124637 ecr 3436985024], length 5: FTP: PWD

16:49:40.698676 IP 192.0.2.1.21 > 198.51.100.1.43250: Flags [P.], seq 439:470, ack 97, win 8195, options [nop,nop,TS val 3436985024 ecr 2894124637], length 31: FTP: 257 "/" is current directory.

16:49:40.699283 IP 198.51.100.1.43250 > 192.0.2.1.21: Flags [P.], seq 97:103, ack 470, win 501, options [nop,nop,TS val 2894124639 ecr 3436985024], length 6: FTP: EPSV

16:49:40.701861 IP 192.0.2.1.21 > 198.51.100.1.43250: Flags [P.], seq 470:518, ack 103, win 8195, options [nop,nop,TS val 3436985029 ecr 2894124639], length 48: FTP: 229 Entering Extended Passive Mode (|||55302|)

16:49:40.702370 IP 198.51.100.1.45294 > 192.0.2.1.55302: Flags [S], seq 955069495, win 64240, options [mss 1460,sackOK,TS val 2894124643 ecr 0,nop,wscale 7], length 0

16:49:40.704474 IP 192.0.2.1.55302 > 198.51.100.1.45294: Flags [S.], seq 2225977054, ack 955069496, win 65535, options [mss 1460,nop,wscale 8,sackOK,TS val 3436985032 ecr 2894124643], length 0

16:49:40.705007 IP 198.51.100.1.45294 > 192.0.2.1.55302: Flags [.], ack 1, win 502, options [nop,nop,TS val 2894124645 ecr 3436985032], length 0

16:49:40.705059 IP 198.51.100.1.43250 > 192.0.2.1.21: Flags [P.], seq 103:109, ack 518, win 501, options [nop,nop,TS val 2894124645 ecr 3436985029], length 6: FTP: LIST

16:49:40.708460 IP 192.0.2.1.21 > 198.51.100.1.43250: Flags [P.], seq 518:573, ack 109, win 8195, options [nop,nop,TS val 3436985036 ecr 2894124645], length 55: FTP: 150 Opening data channel for directory listing of "/"

16:49:40.708618 IP 192.0.2.1.55302 > 198.51.100.1.45294: Flags [P.], seq 1:148, ack 1, win 8195, options [nop,nop,TS val 3436985036 ecr 2894124645], length 147

16:49:40.708618 IP 192.0.2.1.55302 > 198.51.100.1.45294: Flags [F.], seq 148, ack 1, win 8195, options [nop,nop,TS val 3436985036 ecr 2894124645], length 0

16:49:40.708904 IP 198.51.100.1.45294 > 192.0.2.1.55302: Flags [.], ack 148, win 501, options [nop,nop,TS val 2894124649 ecr 3436985036], length 0

16:49:40.708929 IP 198.51.100.1.45294 > 192.0.2.1.55302: Flags [F.], seq 1, ack 149, win 501, options [nop,nop,TS val 2894124649 ecr 3436985036], length 0

16:49:40.709585 IP 192.0.2.1.21 > 198.51.100.1.43250: Flags [P.], seq 573:607, ack 109, win 8195, options [nop,nop,TS val 3436985037 ecr 2894124645], length 34: FTP: 226 Successfully transferred "/"

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Topic review

Re: Allow forcing and or fallback to use of EPSV over IPv4

Re: Allow forcing and or fallback to use of EPSV over IPv4

Re: Allow forcing and or fallback to use of EPSV over IPv4

Re: Allow forcing and or fallback to use of EPSV over IPv4

Allow forcing and or fallback to use of EPSV over IPv4

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