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TCP Acknowledgement and Sequence number


I am using iperf to send a traffic for 60 seconds (i.e. i have an iperf client and iperf server). When I capture the traffic using both Wireshark and tcpdump, almost all of the packets have the same acknowledgement number but different sequence numbers. This is worrying me and is this healthy? Is it OK to have thousands of packets to have the same ack number?

asked 21 Apr '17, 14:09

armodes's gravatar image

accept rate: 0%

One Answer:


There are two Sequence numbers and two ACK numbers - one for each node in the conversation. So if you look at the sequence of the first node going up (which it does during sending data), you should see the ACK numbers of the other node doing the same (acknowledging the sent data).

The node not sending anything will not increase it's sequence number, and so also the ACK number will not increase of the other node. So, in short, what you see is not unusual at all.

answered 21 Apr '17, 15:27

Jasper's gravatar image

Jasper ♦♦
accept rate: 18%