[ale] stalled ftp/sftp transfers

Ken Cochran kwc at theworld.com
Wed May 13 08:24:25 EDT 2009


(Sorry for the top-post, hopefully quicker to read/summarize.)

At the risk of this being OT, Googling this problem gets
results mostly in Linux forums & discussions.  I'd say this
is more an issue of "general networking & network services."

"Local" network is Charter (cable).  Upload speed cruises along
at some 50kb/s-ish for about an hour (hmm) & to about 135mb
then it stalls.  Port status (netstat) looks good, whether I try
PASV or not (ftp is on 20-21 or 20-something-hgh-around 58nnn).
Tcpdump on the data port indicates *nothing* traversing once the
stall happens (well, a packet every minute or two but doesn't
look like any real data).  Netstat shows a send-q from the
beginning & that is maintained during upload so I don't think
that's a factor other than indicating that the output buffer
is filled & working.

Stalling happens on the firewall/NAT machine (directly
connected to the WAN) with ncftp or the OS' (in this case
FreeBSD) command-line ftp client and an OSX machine inside
the NAT/firewall running its command-line ftp client.

Dslreports doesn't have anything, umm... substantive...  umm...  yet...

I'll likely have to resort to drive-net, e.g. more modern
version of the station wagon full of backup tapes... :(

-kc

> Date: Wed, 13 May 2009 07:19:31 -0400 (EDT)
> From: Mike Harrison <meuon at geeklabs.com>
> To: "Atlanta Linux Enthusiasts - Yes! We run Linux!" <ale at ale.org>
> Subject: Re: [ale] stalled ftp/sftp transfers
>
> On Wed, 13 May 2009, Ken Cochran wrote:
>
> > What should I investigate wrt ftp & sftp transfers that stall?
> > I often get sftp downloads that stall and am now rather
> > reliably getting stalls at about 135mb on ftp uploads, both
> > PASV & non-PASV and with ncftp and (I'd guess) "traditional"
> > (builtin) ftp clients.  Server appears to be running Proftpd.
>
> My formerly wonderful, now limited Comcast connection started
> behaving this way a few months ago. Something upstream breaks
> any open connection after x minutes. It affects playing a web radio
> station, or ftp.   So far, rsync over ssh and scp or ssh itself
> seem to be more resilient, and just "hang" for a while
> but then they pick back up. My neighbors are seeing the same.
>
> It seems to break/stall a connection at the port level.
> ie: I can open up another session while one is hung up.
> And then the first one unfreezes in about a minute.
>
> My only point is: It may not be your end, the server, or the gear.
> It may be an ISP along the way trying to limit bandwidth leaching
> net radios, bittorrents, uh.. everything.
>
> Dang I miss the days of 2 DS3's and a Gig-E Upstream connection...


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