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spurious retransmissions and TCP dup ack

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Hello, I am experiencing stability issues with a connection from a windows PC to a embedded Linux using LWIP.

One thing I can reproduce is that I get numerous Spurious Retransmissions and TCP Dup Acks.

Maybe someone can check my tcp dump uploaded to CloudShark Spurious Retransmissions

Thank you for your support.

Regards, Chris

asked 23 Aug '15, 23:28

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christofb
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edited 24 Aug '15, 04:45

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grahamb ♦
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One Answer:

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The trace was taken at the windows machine and it shows that lots of packets from linux get droppoed on their way to the trace point. As linux increments the ip.id per tcp session we can determine that 5 packets at the end of batch get lost (ip.id 7070-7074) between frame 36 and frame 40 and ipids 707a and 707b between frame 48 and frame 50.
Why this happens is not clear to me but I doubt it is the Cisco router dropping those packets. Maybe it has to do with too tiny transmit queue-sizes in the linux stack.

alt text

answered 25 Aug '15, 07:40

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mrEEde
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