V Sat, Sep 04, 2021 at 08:20:57PM +0200, Petr Pisar napsal(a):

Hello,

after upgrading Linux from 5.13.13 to 5.14.0 on my router with this wireless
device:

03:00.0 Network controller [0280]: Qualcomm Atheros AR93xx Wireless Network Adapter [168c:0030] (rev 01)
        Subsystem: Qualcomm Atheros AR93xx Wireless Network Adapter [168c:3116]
        Flags: bus master, fast devsel, latency 0, IRQ 18
        Memory at 81200000 (64-bit, non-prefetchable) [size=128K]
        Expansion ROM at 81220000 [disabled] [size=64K]
        Capabilities: [40] Power Management version 3
        Capabilities: [50] MSI: Enable- Count=1/4 Maskable+ 64bit+
        Capabilities: [70] Express Endpoint, MSI 00
        Capabilities: [100] Advanced Error Reporting
        Capabilities: [140] Virtual Channel
        Capabilities: [300] Device Serial Number 00-00-00-00-00-00-00-00
        Kernel driver in use: ath9k
        Kernel modules: ath9k

which works as a WiFi accesspoint, I noticed that WiFi clients cannot use IPv6
anymore. The problem is that the router cannot translate an IPv6 address of
the client to a MAC address. The reason is that IPv6 multicast packets used by
ICMPv6 neighbour discovery protocol do not reach the clients. In other words
the ath9k-driven device stopped transmitting multicast frames.

The same observation was reported here by Felix Fietkau in "[PATCH] Revert
"mac80211: do not use low data rates for data frames with no ack flag""
<https://marc.info/?l=linux-wireless&m=163091738109000&w=2> with a proposal to
revert the offending d333322361e7a099dc74df2498d3fa5fde5c4fa7 commit.

-- Petr