Re: Large Packages although TSO is off

[Estanislao Gonzalez <estanislao.gonzalez () zmaw de>]

 Hi Martin,

The funny thing is that it is not a VM. The real Problem is that we are 
trying to setup a gridFTP transmission between Germany and UK (a kind of 
parallel FTP), and at some point a package is lost. This package is 
resent periodically, but the receiver never get's it. Other packages 
sent afterward are received, it's just this particular one that can't 
make it through (is not always the same one, but once "missed", it can't 
get through again). It's like something is inhibiting a package from 
being send more than once (which makes no sense to me).

The first thing to notice is that the sender is behind a strict firewall 
dropping ping ICMP packages (and possibly every other ICMP) and we have 
different MTUs (9000 in Germany, 1500 in UK). I suspected this might be 
related to fragmentation (all packages has the don't fragment bit set), 
and the receiver not getting the proper ICMP package, but this shouldn't 
happen in middle of the TCP conversation but while setting it up (I 
think...)

Anyway, that's why I'd like to see exactly what happens on the cable. 
This large packages are obviously not sent as this, but I've already 
turned off segmentation on it (and tried turning every offloading 
feature off). It doesn't matter, I still have large packets with 
checksum errors (to note is that exactly those large packets are the one 
with checksum errors, the others are just fine).

This is the only NIC installed, it appears though as it is not honoring 
the system offloading properties.

I thought I might have missed some wireshark properties. I can't find 
other explanation besides the NIC has to be configured in some other way.

Thanks,
Estani

On 09/27/2010 04:31 AM, Martin Visser wrote:
> The only thing I am wondering is whether you have turned off "tcp 
> segmentation offload" at the physical level of the server, but it is 
> still on at the virtual machine guest level. (You haven't said you are 
> running in virtualised environment, but I had this issue).
>
> Do you think this is causing a network operation issue, or is just 
> that wireshark isn't showing the data you expect?
>
> Regards, Martin
>
> MartinVisser99 () gmail com <mailto:MartinVisser99 () gmail com>
>
>
> On Fri, Sep 24, 2010 at 11:35 PM, Estanislao Gonzalez 
> <estanislao.gonzalez () zmaw de <mailto:estanislao.gonzalez () zmaw de>> wrote:
>
>      Hi,
>
>     I've been reading a lot lately, but I still can't find the source
>     of my
>     problem.
>
>     For example this is a captured package at eth0:
>
>     6249    10.090368       remote.ip       local.ip        TCP    
>     51402>  50383 [ACK] Seq=56628006 Ack=1578 Win=9216 Len=18824
>     TSV=240912663 TSER=21362093
>
>     These are the current settings:
>     # ethtool -k eth0
>     Offload parameters for eth0:
>     Cannot get device udp large send offload settings: Operation not
>     supported
>     rx-checksumming: on
>     tx-checksumming: on
>     scatter-gather: off
>     tcp segmentation offload: off
>     udp fragmentation offload: off
>     generic segmentation offload: off
>     generic-receive-offload: off
>
>     (I've already tried turning checksumming also off)
>
>     The TCP options are set to avoid reassembling streams and not to
>     validate checksums.
>
>     If MTU is set to 9000 for the receiver, and 1500 for the sender,
>     why am
>     I still seeing large packages?
>
>     Any idea?
>
>     Thanks,
>     Estani
>
>     --
>     Estanislao Gonzalez
>
>     Max-Planck-Institut für Meteorologie (MPI-M)
>     Deutsches Klimarechenzentrum (DKRZ) - German Climate Computing Centre
>     Room 108 - Bundesstrasse 45a, D-20146 Hamburg, Germany
>
>     Phone:   +49 (40) 46 00 94-126
>     E-Mail: estanislao.gonzalez () zmaw de
>     <mailto:estanislao.gonzalez () zmaw de>
>
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--
Estanislao Gonzalez

Max-Planck-Institut für Meteorologie (MPI-M)
Deutsches Klimarechenzentrum (DKRZ) - German Climate Computing Centre
Room 108 - Bundesstrasse 45a, D-20146 Hamburg, Germany

Phone:   +49 (40) 46 00 94-126
E-Mail:  estanislao.gonzalez () zmaw de

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