Lenovo ThinkPad T460 Yoga with Intel AC 8260 Wireless Issues

T460-hero

I recently came across an issue where the Lenovo ThinkPad T460 Yoga with Intel AC 8260 wireless adapter was having all sorts of issues connecting to and passing traffic across a Cisco 5508 Wireless LAN Controller with 1262N and 3702E Access Points running 8.0.133.0 software, the most recent release at the time of the issue. The first thing we tried was upgrading the driver for the Intel Dual Band Wireless-AC 8260 to 19.1.0.4 (7/16/2016) which was the latest available at the time. Unfortunately that didn’t help any, we also tried applying an 8.0.135.5 software version to the Cisco WLC, again that didn’t help any.

The laptop would often connect to the SSID but the laptop would be unable to get a webpage to render with all IP traffic essentially stalling. ICMP ping times would jump from 1 ms to 3,900 ms with multiple dropped packets scattered all about the constant ping. Without any load you could occasionally get 1 ms response times for a couple of minutes at a time but the instant you opened a web page the traffic would stall and the ICMP pings would start timing out.

The Intel engineer that was assisting me provided the hint, letting me know that Cisco IT had actually stumbled across this very same issue the week earlier internally with their own employees. Cisco had intentionally disabled A-MPDU on their WLCs, the workaround was to enable A-MPDU for 802.11n on their WLCs. I went ahead and checked our WLCs and sure enough we also had A-MPDU disabled – not exactly sure who or why it was disabled.

802.11n Status: 
    A-MPDU Tx: 
        Priority 0............................... Disabled 
        Priority 1............................... Disabled 
        Priority 2............................... Disabled 
        Priority 3............................... Disabled 
        Priority 4............................... Disabled 
        Priority 5............................... Disabled 
        Priority 6............................... Disabled 
        Priority 7............................... Disabled 
        Aggregation scheduler.................... Enabled 
        Frame Burst.............................. Automatic 
            Realtime Timeout..................... 10 
    A-MSDU Tx: 
        Priority 0............................... Enabled 
        Priority 1............................... Enabled 
        Priority 2............................... Enabled 
        Priority 3............................... Enabled 
        Priority 4............................... Enabled 
        Priority 5............................... Enabled 
        Priority 6............................... Disabled 
        Priority 7............................... Disabled 
    Rifs Rx ..................................... Enabled 
    Guard Interval .............................. Any 

I used the following CLI commands to enable A-MPDU; (note that I had to temporarily disable the 802.11a network to make the change – you’ll want to schedule this off-hours)

config 802.11a disable 
y 
config 802.11a 11nsupport a-mpdu tx priority 0 enable 
config 802.11a 11nsupport a-mpdu tx priority 1 enable 
config 802.11a 11nsupport a-mpdu tx priority 2 enable 
config 802.11a 11nsupport a-mpdu tx priority 3 enable 
config 802.11a 11nsupport a-mpdu tx priority 4 enable 
config 802.11a 11nsupport a-mpdu tx priority 5 enable 
config 802.11a enable 

Why doesn’t the Intel AC 8260 wireless adapter negotiate using A-MSDU?

I hope to be able to bring you that answer from either Cisco or Intel.

I hope you enjoyed the article Tim.

Cheers!

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New Cisco AP 2702i won’t join controller

AIR-CAP1702I-B-K9

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Cisco WLC Bonjour Process Task and Expired Certificates

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It's been a crazy for weeks for me... vacation, consulting engagements, traveling to Reno, NV to stand up a new network - rack, stack, install, configure, test and turnover. So I thought after returning to Philadelphia this past week that things would slow down a little, boy was I wrong. I had a number of challenges and what follows is just one of them involving wireless - I also have another one involving the Lenovo Thinkpad T460 and the Intel AC 8260 Wireless adapter having issues with 802.11n over a Cisco 1262N AP but that's another story. On Wednesday morning […] Read More

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Technical Debt in Networking

counting-money-1239201-scale

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Quality of Service and Traffic Shaping on Cisco Routers

WAR

You have 1Gbps access with 100Mbps port on our WAN link... are you sure you have your router configured properly? A year ago I was asked to investigate why VoIP calls were experiencing poor audio quality across an AT&T AVPN (Ethernet to MPLS) WAN link. After some research and examining the router configuration and logs I realized that the router had never been configured properly to support the 1Gbps access and 100Mbps port. While the router was physically connecting to the AT&T Cisco ONS via 1Gbps, AT&T was only allowing 100Mbps worth of traffic to pass through that connection. In […] Read More

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