Hi,

This sounds like a TCP receive buffer issue with OpenVZ.

What is the advertised window size by your VPS ? You can run tcpdump /
ethereal to get this information.




news-03@foobar.clara.co.uk wrote
> Hi,
>
> I am unable to maintain a TCP connection across the internet to a
> couple of servers for more than a few KB data sent.
>
> After googling the problem, it appears to be very similar to reports
> of 'mtu' issues, however reducing the mtu setting of my local machine,
> the router, and the remote machine seems to make no difference. I'd
> really appreciate any suggestions people can offer...
>
> My setup:
> The local host: Linux 2.4.27
> ADSL router: USR 9003
> The remote hosts: OpenVZ VPS, running Linux 2.6.x
>
> The problem (most obvious symptoms):
> With ssh I can connect to either remote host. Everything seems fine
> until at some point the connection hangs (usually, it seems, while
> typing fast). With scp I can copy small files from local host to
> remote host, but for files >=4k (ish) the connection stalls.
>
> To diagnose the problem, I enabled TCP chargen, echo & discard on one
> of the remote boxes and did a certain amount of testing with netcat.
>
> I found that for data sent from the remote box to the local box I was
> able to transfer several MB without problem. However, for data sent
> from local box to the remote, the connection hung at around 4k-6k data
> sent.
>
> A friend opened TCP echo service on his box for me, and I was able to
> echo several MB through it without issue (i.e. both send & receive).
>
> He also repeated some tests and found no issue with sending from his
> box data to the remote box.
>
> I have two servers (both VPS's), on different networks but both in the
> USA, and both exhibit the same problem. I am in the UK, as is the
> friend who ed with testing.
>
> I do not have any other (noticable) problems with the connection on my
> local machine. It is online 24/7 (via the ADSL router), serves a
> 'hobby' web-site, and I ssh to it from elsewhere on a regular basis.
>
> Based on a google search for similar problems,I have tried reducing
> the 'mtu' setting for eth1 on the local box, as well as the eth
> interface on the router, as well as all eth interfaces on the remote
> VPS. None of this seemed to make any difference, although tweaking
> was done with a certain amount of ignorance so I could still be
> persuaded it is an mtu issue...