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Wireshark-users: Re: [Wireshark-users] Wondering about TCP checksum errors in AFP-over-TCP

From: Kok-Yong Tan <ktan@xxxxxxxxxxxxxxxxxxx>
Date: Sat, 26 Mar 2011 19:07:20 -0400

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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