I have an AP using ath10k as a 5 GHz 802.11ac interface. Very occasionally it gets into a mode where stations are unable to associate. I don’t know how it gets into this mode, but once there the sequence of events when a client tries to associate is:
1. Client and AP exchange Authentication, Association Request, and Association Response frames. 2. AP sends the first packet in the EAPOL exchange. 3. Client sends an AddBA request. 4. AP sends back a malformed AddBA Response. The corruption takes the form of a recognizable AddBA Response appended with 10 bytes of additional stuff, and carrying a bad FCS. Once in this state, every AddBA Response I’ve captured has this extra 10 bytes of stuff appended to the end, and carries a bad FCS. 5. The client discards the AddBA Response because the FCS is wrong. Gathering pcaps on the client shows that it does try to send its EAPOL response, but that packet never makes it onto the air (presumably because the AddBA is pending). Rebooting the client does not resolve the problem, after reboot it still cannot associate. Rebooting the AP resolves the problem. I don’t know a lot about what causes the AP to get into this state. I wrote a script to make clients sit in a loop disassociating and associating every few seconds. A single client running this loop worked for many hours; it never failed. Starting the loop on two clients made the problem happen in about two hours. I have not yet tried it with more clients yet. Because the AddBA Response is generated by the firmware, I believe the problem must be in the firmware. For some reason, it starts sending malformed AddBA Responses. I’ve attached two pcaps, which I’ve trimmed down to manageable size by removing lots of beacons. The Malformed_AddBAR.pcap is from a system in the state where clients cannot associate. The Normal_AddBAR.pcap is captured using the same AP and client, but with everything working normally (the EAPOL exchange completes, and the client begins sending QoS Data frames).
Malformed_AddBAR.pcap
Description: Binary data
Normal_AddBAR.pcap
Description: Binary data
_______________________________________________ ath10k mailing list [email protected] http://lists.infradead.org/mailman/listinfo/ath10k
