TCP Bad Checksum - offloading?

Mar 13, 2010 at 2:46 AM

I'm getting a lot of TCP Bad Checksum in one direction (originating from a particular server).

Read somewhere else that this could checksum offloading - sounds like network interface handles and the capture driver just don't "see" it.
All the data seems to be otherwise fine - no retransmission etc. 

Nothing to worry about?

Mar 15, 2010 at 3:00 AM

If other things are all OK, don't worry about that.

Right now we just assume checksum offloading is always done.  We compare to the SourceNetworkAddress in the IPconfig info, and if so we don’t even check the checksum.

            CheckSumStatus = FormatString("%s",
                  Global.Ipconfig.LocalIpv4Address == SourceNetworkAddress ? "Disregarded" :
                  (ValidateTCPCheckSum(FrameData,
                                                ProtocolOffSet,
                                                frameLength - ProtocolOffset,
                                                Property.DestinationNetworkAddress,
                                                Property.SourceNetworkAddress )
                  ?"Good": "Bad"))

If NetworkInfo(Ex) frame (normally the first or the second frame) is not missing, it may be a parser bug since only a particular server had this problem. Could you share this capture with us in issue tracker? You may only save several frames and erase your sensitive data (uncheck readonly in Edit menu) before submitting.

Thanks,

Luther