SOCKS 5 proxy w/ FTPES problem

[xeon]

Hello,

I have a SOCKS 5 proxy setup between a local machine (Windows 7 using PuTTY's dynamic SSH port forwarding) and a remote server about 50ms away. I'm able to get my full 170Mbps through the proxy when downloading via plain FTP, but if I select FTPES in FileZilla, the download speed will act very strangely. For example, if I queue up several files, sometimes they will transfer at full speed and sometimes they will start going very slowly, sometimes less than 100KB/s and it will remain that low for the entirety of the transfer. Stopping and resuming the transfer can sometimes make it return to full speed again.

[botg]

Which FTP server software is the server running?

FTP over TLS uses a lot more processing resources than plain FTP. What's the CPU usage on the client machine as well as the server machine during a fast transfer and during a slow transfer?

[xeon]

The problem appears to be with PuTTY, perhaps it's not optimized very well for long distance, high throughput scenarios. It starts to limit per connection speeds at around 50ms, but anything 40ms and under appear fairly normal. The higher the latency gets, the more limited it becomes.

I tested on a Linux machine with OpenSSH and it has no such issues, even with higher latency >90ms.

[botg]

Normal PuTTY doesn't deal with high latency well.

The embedded PuTTY components in FileZilla contain some changes to improve performance which ideally should also benefit ordinary PuTTY. If you're willing to try it out, I've created a special PuTTY build for you.


This is the unmodified PuTTY, built on my machine from the latest PuTTY sources: https://filezilla-project.org/codesquid ... y_orig.exe, this serves as reference point to rule out other effects, e.g. difference in used compilers.

This is the above with some small changes in the network code: https://filezilla-project.org/codesquid ... tty_fz.exe, hopefully you should see more performance with this build.

[xeon]

Normal PuTTY doesn't deal with high latency well.

The embedded PuTTY components in FileZilla contain some changes to improve performance which ideally should also benefit ordinary PuTTY. If you're willing to try it out, I've created a special PuTTY build for you.


This is the unmodified PuTTY, built on my machine from the latest PuTTY sources: https://filezilla-project.org/codesquid ... y_orig.exe, this serves as reference point to rule out other effects, e.g. difference in used compilers.

This is the above with some small changes in the network code: https://filezilla-project.org/codesquid ... tty_fz.exe, hopefully you should see more performance with this build.

Unfortunately, there's no change. There's a very consistent limitation of 680KB/s per connection with 85ms of latency.

I tried using SecureCRT and it was limited even lower at <300KB/s per connection. I also tried using Cygwin with the OpenSSH package and even that seems pretty limited, though it was a notable improvement over PuTTY and SecureCRT. It's limited to exactly 16Mbps per connection.