Re: Question about SCP stalling over VPN



I have run into a similar problem, although I don't get any "rcvd
adjust" debug messages -- instead my scp transfers stall -- at a pretty
predictable place too (not exactly, but to within a few megabytes). My
problem ONLY started after I upgraded my kernel (and maybe some other
things :s, from 2.6.19 to 2.6.33). My NFS transfers also started
"stalling", for many minutes (5-15min usually), although they are
retried, and eventually finish. Again, I don't think ANY of these
problems ever happened with my old kernel for a couple years.

During the stalls, netstat says the tcp connection is still
ESTABLISHED, and when I Ctrl-C the stalled scp transfer, the sshd
server logs a "Received disconnect" message. No other debug messages
are shown for me. I'll try to get a tcpdump.


On Fri, 12 Mar 2010 09:13:47 -0500, Matthew Case wrote:
First and foremost, thank you to everyone for your responses. I
checked the MTU on both sides and it's currently 1500 so I'm assuming
it's not a mismatch. My VPN is a pair of old Netscreen 5xp boxes, and
I can't find anything relating to MTU or packet size in the
configuration, but I'm still looking.

Secondly, to answer your question John, There is no persistent
connection between the servers. I could feasibly set up an NFS share
between the two but I have a sneaking suspicion that if the problem
is some sort of packet mangling by the VPN during file transfers, the
actual mechanism used to transfer the file will be irrelevant.
However, I will set this up and test it and report back my results,
most likely next Monday.

On 3/12/2010 3:41 AM, John Morrison wrote:
Matt,

If you are using ssh do you need to use scp as well? Or is just
plain copy ok?

On 10 March 2010 03:04, Darren Tucker<dtucker@xxxxxxxxxx> wrote:

Matthew Case wrote:
[...]

I've looked high and low and haven't really come up with anything
definitive. Someone somewhere had mentioned fiddling with MTU
settings, but I'm not really sure what that will accomplish as I
am unfamiliar with what MTU is and does. If this question has
been answered previously, I apologize ahead of time. Thanks!

This does sound like the MTU problem to which you refer. See
http://www.snailbook.com/faq/mtu-mismatch.auto.html for details.