TCP Invalid checksum errors

Discussion in 'Capsa Network Analyzer' started by craigdchang, Apr 29, 2009.

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  1. craigdchang

    craigdchang Registered Member

    Mar 27, 2009
    I currently have colasoft Capsa 6.9 Enterprise edition installed on a Dell Latitude D600 laptop at one of our remote locations.
    The location consists of about 50 workstation connected to 3 HP Pro curve switches. I have a hub connected between the switch and the router (which is a 512meg dedicated frame back to our home office). The laptop is plugged into the hub.
    I vnc into the laptop to watch the network traffic. When I check the diagnosis tab I noticed that the TCP invalid checksum is almost as high as the whole transport layer. I also am getting hundreds of DNS Host or Domain not exist errors.
  2. Stem

    Stem Firewall Expert

    Oct 5, 2005
    For the Invalid Checksum errors, check your NIC card settings on your laptop (Hardware-device manager), and disable the "Hardware checksumming".

    - Stem
  3. Nelson

    Nelson Registered Member

    May 26, 2005
    TCP Invalid checksum errors may comes from two possibility:
    1) as what Stem told, the enabled NIC "Hardware checksumming" can cause it.
    2) since you are using a hub to fetch the network traffic, there is a collision domain with 3 talker in. The link between the switch and the router is working in half duplex mode which encounters collisions a lot. This is exactly what you should see by the hub plugin diagram. For 50 stations, this is torlerable. If it bothered you, I suggest you use SPAN (port mirroring) instead of the hub.

    The DNS diagnosis is based on the DNS server response, so if there are many, then there are.
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