WLC 2504: FlexConnect throughput lower than Local mode.

[sardarjion]

My setup is:

1. RVS4000 router connected to internet. 
2. WLC 2504 v8.5.182.0 connected to LAN port 1 of RVS 4000.
3. Two 2702 APs connected to LAN port 2/3 of RVS 4000 and power via DC adapter.

My internet connection maxes out at 350mbps. The device under test is iPhone13 and using speedtest app. My understanding is that FlexConnect mode doesn't route the data traffic back to WLC and will drop it first switch ( router in my case). As a result, I should see a slight improvement in speedtest and touch close to 350mbps mark. However, the test says the opposite. 

Local mode (10 times)

• Average Speed: 335-340mbps
• Ping: 20-22ms.

FlexConnect (10 times)

• Average Speed: 300-310mbps
• Ping 22-25ms

I am not sure if some setting causing this but I don't which logs should I analyze to debug this further. The drop in performance is significant. 

[Rich R]

So let's be clear about terminology first:
Local mode - all WLANs are CENTRALLY switched on the WLC.  Client traffic is tunnelled from AP to WLC over CAPWAP.
Flexconnect mode - WLANs can be centrally switched (same as local mode) or locally switched - direct breakout to VLAN on AP port.
Since this is all local I wouldn't expect to see much difference but all other things being equal I'd expect flexconnect local switching might be slightly quicker because it's 1 hop less and taking the CAPWAP tunnel out of the equation.

Can't think of any reason why it should be the other way around so look at port stats/errors, get packet captures and look at possible differences like TCP MSS, fragmentation etc