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TCP checksum incorrect while trying to ftp file RRS feed

  • Question

  • I have a laptop with Windows xp & service pack 3 installed and I am trying to ftp a file to one of our machines. I noticed that the TCP header checksum comes out to be incorrect, around the same part of the file every time I transfer. The tcp retransmissions also have bad checksums. It only happens in a particular packet. I used wireshark to sniff the packets and wireshark also flags it as incorrect checksum. The computer's ip address is 192.168.1.101 and blue packet is the one that's causing issues.

    What's interesting is that when I use another computer, with windows xp and service pack 3 and ftp the same file, I don't see the tcp checksum error. But in the latptop it's reproducible every time. Also, other tcp services, like telnet,works fine. What I noticed in bad packet sent from the laptop was that the push flag in the tcp header was getting set. For other packets it's not set. I am wondering if the flag is getting set but the checksum isn't accounting for this.

    Has anyone seen such an issue with the tcp stack? Thank you in advance

     

    Thursday, October 20, 2011 2:59 PM

Answers

  • The problem is created by your NIC settings. If you go into the properties of your nic driver you should look for something like "TCP Checksum offload" and/or "IP Checksum offload" and disable these settings. Then the problem should go away.

    regards

    richard

    Friday, October 21, 2011 12:11 PM

All replies

  • The problem is created by your NIC settings. If you go into the properties of your nic driver you should look for something like "TCP Checksum offload" and/or "IP Checksum offload" and disable these settings. Then the problem should go away.

    regards

    richard

    Friday, October 21, 2011 12:11 PM
  • Hi Richard,

    Thank you very much. I turned off the 'Offload Transmit TCP Checksum' and it worked!'


    RG
    Friday, October 21, 2011 2:48 PM