TCP connections stall when station re-associates.
Subsystems (2)
We're seeing something funny while testing ath9k and ath5k with multiple VIFs. We are using send-to-self routing rules and have a TCP connection going between two station interfaces connected to the same AP. Kernel is ~2.6.37 (wireless-testing from a few days ago, plus some local patches). We tried commercial APs and ath9k/ath5k APs running 2.6.37 kernel and hostap with similar results.
The problem is that when the stations loose association and re-associate (and maybe other times as well), the TCP connections often hang. I see buffers in the sendq in netstat, and retransmits on the wire, but it seems to make no progress.
Here's a pair of sockets with one side in the state:
tcp 0 7312 7.7.1.54:33513 7.7.1.56:33514 ESTABLISHED tcp 0 0 7.7.1.56:33514 7.7.1.54:33513 ESTABLISHED
Here's a brief snippet from the interface with 7.7.1.56 on it:
51.517954 7.7.1.56 -> 7.7.1.54 TCP 33514 > 33513 [PSH, ACK] Seq=64229 Ack=1 Win=63 Len=12 TSV=8209159 TSER=7621148 51.521719 7.7.1.54 -> 7.7.1.56 TCP 33513 > 33514 [ACK] Seq=13 Ack=64241 Win=377 Len=0 TSV=8209162 TSER=8209159 52.279788 7.7.1.54 -> 7.7.1.56 TCP [TCP Retransmission] 33513 > 33514 [PSH, ACK] Seq=1 Ack=64241 Win=377 Len=12 TSV=8209920 TSER=8209159
The TCP connection is trying to run at 9.6kbps, sending 1460 bytes per 'send' call.
If I start a UDP connection on the same pair of ports it runs fine, even while the TCP connection is hung.
I am curious if anyone has any suggestions for debugging this further, for instance, some way to see why the TCP connection is not making forward progress.
Thanks,
Ben
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Ben Greear <greearb-my8/[email protected]> Candela Technologies Inc http://www.candelatech.com -- To unsubscribe from this list: send the line "unsubscribe linux-wireless" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
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Quoted 8 lines · Ben Greear
We're seeing something funny while testing ath9k and ath5k with multiple VIFs. We are using send-to-self routing rules and have a TCP connection going between two station interfaces connected to the same AP. Kernel is ~2.6.37 (wireless-testing from a few days ago, plus some local patches). We tried commercial APs and ath9k/ath5k APs running 2.6.37 kernel and hostap with similar results.
When the stations re-connect, we re-run dhcp client, which involves setting IP to zero and then re-acquiring the IP address. We then set up new routing rules, etc to have it back to the way it was before the station lost contact with the AP.
The TCP/IP connections are specifically bound to local IP and port.
Maybe it is invalid to expect TCP connections to survive this IP change?
I'll work on reproducing this DHCP behaviour on some regular wired interfaces and see if I can reproduce in a simpler test case.
Thanks,
Ben
Signature · 6 lines
Ben Greear <greearb-my8/[email protected]> Candela Technologies Inc http://www.candelatech.com -- To unsubscribe from this list: send the line "unsubscribe linux-wireless" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html