Wireless clients sporadically getting Limited Connectivity, APs dropping packets

[John_Rowler]

We have a pair of V2110 wireless controllers and around 400 3825i access points. Controller firmware is 09.21.06.0002. AP firmware is 9.21.27.1387X.

About 4 months ago we noticed a problem where the APs would just drop traffic. A packet capture will show a ping coming into the radio from the client, going out the Eth interface on the AP, the reply coming back into the Eth interface, and never going out of the radio.

A particularly strange detail is that this only happens with certain source/destination traffic. For instance a client cant ping the gateway of 10.1.20.1/24. but cannot pint the server at 10.1.20.2. Since we can see the ping making it to the server and the ping reply making it back to the AP, we know it's not a firewall/ACL/routing issue on any other part of the network. The traffic disappears at the AP. Clients cannot communicate with anything on the Internet or any of our servers (DNS, DHCP, etc.) during this time. They can ping gateways in any subnet but that's it; everything else is failed.

More details:

-We've gone through several firmware updates with GTAC. Nothing has helped.
-The issue can affect any client on any AP in any location at any time.
-The issue is intermittent; it may happen every few minutes or once per month to a particular client in a particular area. Once failed it may last for seconds or days.
-While it's affecting one client, other clients on the AP may be working fine or may also fail.
-It can happen on either 2.4 or 5.7GHz.
-It can affect any type of client (phone, laptop, tablet) and any OS.
-Restarting the client or AP will sometimes fix the issue, sometimes not.
-It happens with our without using NAC, or any other type of authentication. It happens on completely open networks as well.
-It happens on both bridged at AP and bridged at controller topologies.
-It's not limited to a particular subnet or VLAN.
-It happens with or without Flexible Client Access enabled.
-It happens on either controller.
-GTAC hasn't made much progress on the issue in 4 months.

[JP4]

What firmware, 9.21.08 ?

[Chat]

It's sounds great!!

[James_A]

OK, with our other bigger problems being solved in 09.21.08, now I think we're seeing this problem clearly. I need to get an eth0 trace, but I just had one client where it would retransmit the initial SYN packet 13 times, give up, then I'd try again a minute later and after 10 retransmitted SYNs get a SYN/ACK back from the server.

We also see clients having problems connecting, I saw one this morning that bounced around 5 APs, briefly connecting but not getting to EAP before finally connecting properly several minutes later.

[James_A]

I have my eth0 trace, and I can see the SYNs going out on the wire from the AP's point of view, however it's not until the client ARPs again for the server's IP that things start working. Now to run wireshark on the server as well. OK, the server's ARPs are going unreplied to, eth0 on the AP can see them OK. Final test, capture on the server and then on wifi1, the ARP isn't making it into the air.

So there's a problem with some broadcast packets making it onto the air, which correlates with FES's observation about the broadcast rekey interval.

[JP4]

Doug, were do we stand on the 9.21.08 code ? Have further problems been identified or are the problems more related to site specific configuration issues ?