In order to resolve a reoccurring communications problem of a HMI (former Ubuntu 14.04; now Debian 8) with LTi ServoOne controllers, network traffic was captured on the HMI.
The HMI is connected to its clients, via a standard 5-port consumer switch.
When using such a cheap switch, which was around the first time simulating this, the communication error was observed more frequently. (This seems to simulate a bad transmission line)
Using a "port-mirroring" capable switch
As I doubted the caps, I tried capturing on a 3rd machine, through an expensive switch with port-mirroring capabilities. Within 48hours, I was not able, to recapture retransmissions.
- After a retransmission of a HMI request, the client would respond more quickly (~3ms) than it would on a normal request (5..7ms).
- The client ACKs with an incorrectly raised SEQ number
- After a long delay (500..700ms) it would finally send a valid response to the retransmission request
!Client config has not changed!
Now the client handles the retransmission request as intended:
- normal response time
- ACK is correct
How can the clients respond correctly under Debian?
Does Wireshark miss something, that would explain the different behavior of the clients?
(Would the different kernel-configs prevent Wireshark from capturing any (invalid) packets?)
- Is there any sane explanation for the difference in this behavior?
Of course, are the captures available:
asked 29 Jan '15, 05:23
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