buglwIP - A Lightweight TCP/IP stack - Bugs: bug #62302, LWIP 2.0.2 / Xilinx Zynq: TCP hang...


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bug #62302: LWIP 2.0.2 / Xilinx Zynq: TCP hang data transmission after packets loss events

Submitter:  Nir <nirshem>
Submitted:  Tue 12 Apr 2022 10:17:06 AM UTC
Category:  TCP Severity:  3 - Normal
Item Group:  Faulty Behaviour Status:  None
Privacy:  Public Assigned to:  None
Open/Closed:  Open Planned Release:  None
lwIP version:  2.0.2

Tue 12 Apr 2022 10:17:06 AM UTC, original submission:  


An issue Iā€™m working on for a while.

My setup as follow:

1) Unit A: Embedded unit: Xilinx board (Zynq 7020) running FreeRTOS +LWIP 2.0.2
2) Unit B: PC client running WIN10

Connectivity between the units is fiber ā€“ and I added sniffer in the middle for debugging of the issue.

Unit A transmit in TCP (LWIP 2.0.2) data at around 1.7[Mbps] to unit B.

The problem: after hour of system running the throughput is dropped to zero (except of TCP keep alive) and return back after around 6 seconds.

After reviewing the Wireshark in the middle (connected via sniffer) I found a 3 dup acks event that cause fast retransmission reply,

From that moment the Application traffic stopped for 6 seconds and only TCP keep alive was active.

After checking the location of the packet loss I can tell for sure it was in the PC side (running Iperf UDP test client /server locally shows some packet loss due to the load on the PC).

I attached two wiresharks files of two events.

Now my question are:

1) Why there is a drop in the traffic from Unit A ?

2) Why Fast recovery is not working as it should after fast retransmission event ?

3) Is there a way to fix it by timers/windows size configuration ?

4) Is there a known issue about it ? ā€“ I looked on the change log since 2.0.2 and haven't found something special.

Any help here will be much appreciated.

Nir <nirshem>


(Note: upload size limit is set to 16384 kB, after insertion of the required escape characters.)

Attached Files
file #53079:  Event_1.pcapng added by nirshem (123KiB - application/octet-stream)
file #53080:  Event_2.pcapng added by nirshem (286KiB - application/octet-stream)


Depends on the following items: None found

Items that depend on this one: None found


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    Follow 4 latest changes.

    Date Changed by Updated Field Previous Value => Replaced by
    2022-04-12 nirshem Attached File- Added Event_1.pcapng, #53079
        Attached File- Added Event_2.pcapng, #53080
        Carbon-Copy- Added -email is unavailable-
        Carbon-Copy- Added -email is unavailable-

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