Networking – Interpret Wireshark Captures

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I am troubleshooting wireless connectivity problem in my home network. My Thinkpad X200 laptop which use Intel Wifi Link 5100 AGN is not able to surf the internet stably. Sometimes it works, but most of the time it couldn't load the page completely or not loaded at all.

This is not happening to my desktop PC which is connected to the same D-Link AP as well.

I managed to capture network traffic on my laptop with Wireshark which results in the image below:

alt text

From what I know, the black-background rows show that there are erros in TCP checksum / Bad TCP. Is this normal on any wireless network? If not, how can I fix my laptop so it can surf the internet stably as my desktop PC?

Edit: I tried to capture the TCP packet again while the page failed to completely load. It looks like this is related to massive "TCP Retransmission" in Wireshark logs somehow ..

Edit 2: Gave up on investigating this. Tried another ACP. Luckily, it works without those many retransmission message o__o' Many thanks to everyone for the answers!

Best Answer

TCP checksum / Bad TCP is very normal for Wireshark and other packet sniffing tools, it is because you have enabled the checksum offloading on your wireless card, you can disable it or ignore it.

TCP retransmission is the exact reason for the problems of your network.

The possible reasons are below:

  • The acknowledgment packets are being transmitted via a slower path.
  • The network load is very high.
  • The receiver or router is overloaded.
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