TCP Invalid checksum errors

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

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  1. craigdchang

    craigdchang Registered Member

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    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

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    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

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    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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