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

[Martin Visser <martinvisser99 () gmail com>]

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


On 27 March 2011 10:07, Kok-Yong Tan <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,
> doubleclick.com, etc., and even my externally hosted mail server.
>
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>
>
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