Re: [lwip-users] Duplicate ACKs

[Zach Smith]

Looking at the Seq and Ack numbers, my guess is that your embedded controller 
quit receiving for some reason. (problem in driver maybe???)

It's a little confusing since they are sending and receiving the same amount of 
data back and forth to each other which makes the Seq#'s and Ack#'s the same 
but here is what it looks like to me:

Packet 90: 172.16.1.23 --> 172.16.1.34    Seq: 485,    Ack: 485
Packet 91: 172.16.1.34  --> 172.16.1.23 *Seq: 485*, Ack: 496
Packet 92: 172.16.1.23 --> 172.16.1.34    Seq: 496,   *Ack: 485*
If 1.23(embedded ctrlr) received packet 91 from the PC then it should reply 
with  a Ack # of 11 bytes more than the Seq # of pkt 91 which would be 496.
You can see in packet 92 that 1.23 increased its sequence # (from 485 in pkt 90 
to 496 in pkt 92) but not the Ack # which to me suggests that it never received 
packet 91 from the PC.
So, since 1.23 didn't get pkt 91 from the PC it keeps sending the Ack that it 
sent in pkt 90 because it thinks the PC never received it.
And the PC keeps sending pkt 91 over and over until eventually the connection 
times out.

-Zach

-----Original Message-----
From: address@hidden [mailto:address@hidden On Behalf Of Daniel Haslimann
Sent: Thursday, June 27, 2013 2:02 AM
To: address@hidden
Subject: [lwip-users] Duplicate ACKs

Hi Everybody

I am facing a problem with our embedded controller (stellaris) running lwip 
1.3.2.

What I am doing in the test, is running telnet traffic over days. It ran well 
for about 3 days, and then suddenly the PC receives a lot of DUP ACKS and times 
out.

I have attached the wireshark log.
The PC has the IP 172.16.1.34 and the embedded controller running lwip
172.16.1.23

I have not enabled any debugging in the test, but will enable it now.
But this can take another 3 days till I get any new results.

I appreciate any hints about this.

Regards,
Daniel

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