ncat proxy starts to error out frequently after running for a few hours

[Scott Gifford <sgifford () suspectclass com>]

Hello,

I'm helping a friend of mine use ncat on Windows as a simple proxy.  The
situation is very interesting: an old Windows 2013 host needs to transfer
many GB data to AWS, but the TCP send window size in Windows 2013 is so
small that it can only push 1.5 Mbps through a 40 Mbps connection with 75ms
latency.  By proxying through a newer Windows host with a saner TCP stack
(in the same data center, so latency is very low), transfer speed goes up
to 30Mbps, so a huge win for ncat!

Unfortunately, after awhile, ncat starts frequently reporting this error,
and grinds to a halt:

Ncat: An existing connection was forcibly closed by the remote host.


It doesn't say whether that's the AWS host or the Windows 2013 host, so I'm
not sure which end it is.

What's weird is that stopping ncat and restarting it makes the problem go
away, at least for awhile.  Unfortunately there is a lot of data to
transfer, so watching for this and pressing CTRL-C is not practical.

The command-line he's using is:

ncat --listen 5200 --keep-open --sh-exec "ncat 10.0.1.8 1433"


Similar to what's suggested here:

https://nmap.org/ncat/guide/ncat-tricks.html#ncat-chain


Does anybody know any likely causes of this error, or if it's something
that is fixed in a later version of ncat?  Or anybody have other
suggestions on how to approach this?

Thanks!

-----Scott.

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