![]() One example of a possible “non-error error” is when you see a lot of “TCP CHECKSUM INCORRECT” messages during a file copy operation. Don’t be too concerned if you see some packets that appear this way – it might indicate a problem, but then again it might not. For example, if Wireshark detects potential problems, it colors them with red text on a black field. The networks are unreliable and do not guarantee the delay or the retransmission of the lost or damaged packets.One of the features of Wireshark that you may have noticed, if you’ve been reading my posts this week and doing some experimenting on your own, is that the program color-codes packets in the packet list pane. Here, retransmission is a mechanism used by protocols such as TCP to provide reliable communication. ![]() ![]() The TCP retransmission means resending the packets over the network that have been either lost or damaged. ![]() There are four common reasons for packet retransmission: (1) the lack of an acknowledgement that data has been received within a reasonable time, (2) the sender discovering that transmission was unsuccessful (usually through out of band means), (3) the receiver notifying the sender that expected data hasn't been. Common reasons for retransmissions include network congestion where packets are dropped (either a TCP segment is lost on its way to the destination, or the associated ACK is lost on the way back to the sender), tight router QoS rules that give preferential treatment to certain protocols, and TCP segments that arrive. ![]()
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