[lwip-devel] [bug #29080] Burst of duplicate ACKs

[Simon Goldschmidt]

Update of bug #29080 (project lwip):

                  Status:                    None => Need Info              

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Follow-up Comment #1:

First: Please append pcap files we can view in wireshark, not text-files that
are harder to read and contain less details. Without having the complete log,
I can only guess what's going wrong.

Now to 1):

The "bursts" of duplicate ACKs are OK: if one packet goes missing (one of the
packets 114 to 123, I guess - details would be in the pcap file), lwIP sees
the next packet having a sequence that it doesn't expect and so sends an ACK
for the last received seqno to tell the other side about the lost packet.
Wireshark marks this as "Dup ACK" as the data has already been ACKed before.
As this is done for every received packet, more than one duplicate ACK is
received.

The remote side goes into fast-retransmission after receiving two duplicate
ACKs (packet #126) and eventually, lwIP has received all data and ACKs it all
(packet #146: Ack= increases from 94901 to 96361).

As to 2): That looks indeed strange but I cannot say anything here without
the pcap file. From the assert, it looks like the sender overran our receive
window. Although that would be strange, we probably shouldn't assert...?

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