I did some orginal captures on a computer sitting outside our firewall and saw alot of TCP DUP ACK/TCP Retransmission while web browsing. Thought I was having an ISP issue but their testing is indicating no trouble. I thought this message indicated dropped frames. Am I incorrect?

I did another capture between two computers on a 24 port switch, no Internet, no connection other than to each other. One computer coping data from the second and the third doing the capture. I still see this messages.

This capture is me going to Foxnews

https://www.cloudshark.org/captures/81fc503552a8

Can someone explain is this normal? Thanks

asked 07 May '13, 10:46

dmcmasters's gravatar image

dmcmasters
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accept rate: 0%


TCP has this inherent mechanism of recovery. In tcp stream eq 8 of your trace there was a condition of retransmission generated due to timing but not because of drops. Here is the snippet of your trace.

Step-1)Server send a packet to client(Let us call it packet-A){Packet.no-150}

Step-2)Client acknowledged the packet (Let us call it ack-A){Packet.no-192}

Step-3)Somehow packet-A was retransmitted by Server.The reason might be the delay in receiving ack-A from client and ack timer got out and retransmission timer got kicked in.(Dup of Packet-A){Packet.no-194}

Step-4)Client generated a duplicate ack for the retransmitted packet.(Dup of ack-A){Packet.no-195}

It is not always implies to losses whenever you see these retransmissions and duplicate acks.How timers got implemented also plays a role. With that said leaving to expert opinions....

link

answered 07 May '13, 17:33

krishnayeddula's gravatar image

krishnayeddula
599303546
accept rate: 6%

edited 07 May '13, 20:13

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Asked: 07 May '13, 10:46

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Last updated: 07 May '13, 20:13

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