WinSCP client with passive FTPs and multiple outgoing NAT GWs is intermittently failing :: Support Forum

bhuffman
Joined:: 2023-02-15
Posts:: 2

WinSCP client with passive FTPs and multiple outgoing NAT GWs is intermittently failing

2023-02-15 22:20

Hello,
We are using WinSCP to connect to a third-party FTPs (explicit TLS) server. Our connection to the internet is through redundant NAT GWs and the selection of the NAT GW is random (perhaps roundrobin?)

We're getting intermittent failures trying to download files from the third-party server. I'm not sure why, but I'm guessing that the FTPs server sees multiple connections from the different public IPs of the NAT GWs and is refusing the connections.

When it fails, we see this in the logs:

. 2023-02-13 09:52:10.767 Retrieving directory listing...
> 2023-02-13 09:52:10.767 TYPE A
< 2023-02-13 09:52:10.767 200 TYPE is now ASCII
> 2023-02-13 09:52:10.767 PASV
< 2023-02-13 09:52:10.767 227 Entering Passive Mode (a,b,c,d,218,200)
> 2023-02-13 09:52:10.767 MLSD
. 2023-02-13 09:52:10.767 Connecting to a.b.c.d:56008 ...
. 2023-02-13 09:52:10.767 Data connection closed
. 2023-02-13 09:52:10.767 <Empty directory listing>
. 2023-02-13 09:52:25.689 Timeout detected. (control connection)
. 2023-02-13 09:52:25.689 Could not retrieve directory listing
. 2023-02-13 09:52:25.689 Connection was lost, asking what to do.
. 2023-02-13 09:52:25.689 Asking user:
. 2023-02-13 09:52:25.689 **Lost connection.** ("Timeout detected. (control connection)","Could not retrieve directory listing")
< 2023-02-13 09:52:25.689 Script: Lost connection.
< 2023-02-13 09:52:25.689 Script: Timeout detected. (control connection)
< 2023-02-13 09:52:25.689 Could not retrieve directory listing

Are there any settings in WinSCP that would make it handle this situation?

Thank you!
Brian

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martin◆ Site Admin
Joined:: 2002-12-10
Posts:: 41,518
Location:: Prague, Czechia

Re: WinSCP client with passive FTPs and multiple outgoing NAT GWs is intermittently failing

2023-02-16

Is the a.b.c.d FTP server's IP or NAT GWs' IP? Can you post complete log(s) that show both a successful transfer and a failed one? Do you have the problem with WinSCP only? Or with any FTP client?

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bhuffman
Joined:: 2023-02-15
Posts:: 2

Re: WinSCP client with passive FTPs and multiple outgoing NAT GWs is intermittently failing

2023-02-17 16:05

a.b.c.d is the vendor's FTP server IP.

See attached logs with successful transfer (performed from a different location that has only a single outbound NAT GW) as well as the logs with issues.

I believe we were able to make this work with FileZilla in the past. But I'm unable to reproduce a successful transfer with FileZilla now.

Regards,
Brian

sFTPVendorProject_Good.log (28.94 KB)

sFTPVendorProject_Issues.log (57.62 KB)

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martin◆ Site Admin
Joined:: 2002-12-10
Posts:: 41,518
Location:: Prague, Czechia

Re: WinSCP client with passive FTPs and multiple outgoing NAT GWs is intermittently failing

2023-02-20

Before you wrote that the problem is intermittent. But from your last post it looks like you cannot transfer at all via the roundrobinned GWs.
I wanted logs of successful and failed transfer over the same setup (roundrobinned GWs) – assuming the problem is intermittent.
Though if you cannot transfer using other clients either, then it does not seem like WinSCP issue.

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WinSCP client with passive FTPs and multiple outgoing NAT GWs is intermittently failing