Re: Wondering about TCP checksum errors in AFP-over-TCP

[Anders Broman <a.broman () bredband net>]

Kok-Yong Tan skrev 2011-03-27 16:51:
> It says that "Wireshark 1.2 and above disable IP, TCP and UDP checksum 
> by default."  Does this mean that it disables checksum [validation] by 
> default?  If so, note that I'm running Wireshark 1.4.3 with default 
> settings on a MacOS X 10.5.8 system and I'm still seeing the TCP 
> checksum errors.
If you upgraded from an earlier version your (old)preferences will be 
retained...
/Anders
> On Sun, Mar 27, 2011, at 01:19, Martin Visser wrote:
>
> > In pretty much all case where you are seeing TCP checksum errors on a 
> > server, it will because of the various TCP offload features of the 
> > NIC / driver. If can capture on the wire (that is using 
> > port-mirroring on a switch) this will confirm this, or alternatively 
> > turn off those features on your server temporarily while testing.
> >
> > See http://wiki.wireshark.org/CaptureSetup/Offloading for details
> >
> > Regards, Martin
> >
> > MartinVisser99 () gmail com <mailto:MartinVisser99 () gmail com>
> >
> >
> > On 27 March 2011 10:07, Kok-Yong Tan <ktan () realityartisans com 
> > <mailto:ktan () realityartisans com>> wrote:
> >
> >
> >     On Sat, Mar 26, 2011, at 18:53, Kok-Yong Tan wrote:
> >
> >         Just for kicks, I decided to do a wireshark trace of
> >         AFP-over-TCP conversations between my Apple MacOS X 10.4.11
> >         Tiger server and my Apple MacOS X 10.5.8 Leopard (PPC)
> >         client.  Surprisingly, I'm seeing lots of TCP checksum errors
> >         (no ssh going on here in the connection since it's all
> >         protected on my internal LAN) on packets going in both
> >         directions.  Now, if the TCP stack were damaged either on the
> >         client or the server or both, I would expect connection
> >         issues and all packets going through to exhibit the checksum
> >         errors.  But I don't and not all packets are exhibiting
> >         checksum errors between the two machines.  Only some.  Of
> >         course, this is manifesting itself in slower than expected
> >         throughput between the server and client since I assume that
> >         TCP checksum errors result in retransmits.  The server is
> >         connected to a ZyXEL GS2024 switch via LACP 802.3ad with 1 IP
> >         address in use in the two-NIC bonded pipe.  Could this be
> >         causing the TCP checksum errors?
> >
> >
> >     More info on this:  I'm beginning to think that the
> >     LACP/IEEE802.3ad bonding of the server with the switch has
> >     nothing to do with it as I'm seeing the same checksum errors
> >     between the client (which only has one NIC and doesn't use
> >     LACP/IEEE802.3ad) and public servers hosted at akamai.net
> >     <http://akamai.net>, doubleclick.com <http://doubleclick.com>,
> >     etc., and even my externally hosted mail server.
> >
> >     --
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> >
> >
> >
> >
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> Reality Artisans, Inc.             #   Network Wrangling and Delousing
> P.O. Box 565, Gracie Station       #   Apple Certified Consultant
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>
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