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Subject: Re: Delay sending packets after a wireless roam
To:     Michael Johnson <mjohnson459@gmail.com>,
        linux-wireless@vger.kernel.org
References: <CACsRnHWa47zpx3D1oDq9JYnZWniS8yBwW1h0WAVZ6vrbwL_S0w@mail.gmail.com>
From:   Ben Greear <greearb@candelatech.com>
Organization: Candela Technologies
Message-ID: <42b5d899-b791-1fed-b2a0-1e96028f5eb5@candelatech.com>
Date:   Mon, 30 Aug 2021 06:53:45 -0700
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On 8/27/21 3:23 AM, Michael Johnson wrote:
> Hi all,
> 
> I'm having an odd issue with wireless roaming whereby any time I roam
> from one access point to another I start receiving packets almost
> instantly but experience a delay of roughly 1 second before I can send
> packets out. I think I've narrowed it down to somewhere kernel related
> but I'm struggling to know where to look next.
> 
> Firstly, I started seeing this delay after upgrading from Ubuntu 16.04
> (so 4.15 kernel) to 20.04 (tested with 5.4, 5.8 and 5.11) but I also
> tested this on Kali 2021.2 (5.10).
> I see the delay with intel (iwlwifi), qualcomm (ath10k), and realtek cards.
> I've also used both iwd and wpa_supplicant, with and without
> systemd-networkd and NetworkManager.
> I've been using ICMP for testing but I've also tried a python script
> for sending udp packets with the same result.
> 
> Here is the output of the simplest test that still shows the issue
> (ping + tcpdump + iwd + 5.11.0-27-generic):
> https://pastebin.com/92TKKktb
> 
> My naive tl;dr of that data is:
> 
> 30.322638 - we start to roam which falls between icmp_seq=121 and icmp_seq=122.
> 30.415411 - roam is complete
> 30.424277 - iwd is sending and receiving neighbor reports over the link
> 31.358491 - an ARP request is sent out  (should the ARP cache be
> cleared on a roam?)
> 31.367930 - ARP response
> 31.368009 - packets start being sent again as soon as we get the ARP response
> 
> Can anyone help me understand what might be happening between the
> interface going "up" at 30.415411 and the ARP request at 31.358491
> please?
> Also, does anyone else see something in their environment?

I think ARP cache should be cleared on roam...I'm not sure how best to do that
though.  wid/supplicant could make the call to clear as soon as roam happens?

Thanks,
Ben

-- 
Ben Greear <greearb@candelatech.com>
Candela Technologies Inc  http://www.candelatech.com