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ACK after PSH,ACK from same source.


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While capturing the pcap,i had found some issue like, same source sends PSH,ACK and ACK.Below is the attached screen shot.Is it possible like that.

asked 01 Aug '17, 04:21

kodamagulla_kalyan's gravatar image

accept rate: 0%

edited 01 Aug '17, 04:22

One Answer:


Sure, that's possible. PSH/ACK just means "this is something the receiver can process right away" - it doesn't mean that there can't be more following it.

answered 01 Aug '17, 04:36

Jasper's gravatar image

Jasper ♦♦
accept rate: 18%

Can you please elabrate below q.

Say in PSH,ACK from x to y seq = 7732 ack =1 len =831. immediate ACK from x to y seq = 8563( 7732 + 831) ack =1 len = 1448 happens.

So why it has to send again ACK with adding seq with len ? I was assuming this has to be done by the reciever end.


(01 Aug '17, 04:49) kodamagulla_...

ACK is only increased by the receiver if TCP payload bytes (len value) arrived successfully. If x sends two packets in a row, ACK must not change because nothing was received from y in the meantime.

(01 Aug '17, 04:55) Jasper ♦♦