BBS:      TELESC.NET.BR
Assunto:  Re: Uodate on PI wifi bridging issues.
De:       The Natural Philosopher
Data:     Thu, 5 Feb 2026 14:27:51 +0000
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On 05/02/2026 14:04, Lars Poulsen wrote:
> On 2026-02-04, The Natural Philosopher  wrote:
>> If you remember I had constricted a bridge from wifi to ethernet to act
>> as a bridged access point. On a PI 4B as a test platform
>>
>> The problem was that whilst the bridge was reasonably OK accessing my
>> LAN, up to 90% packet loss was experienced when accessing the internet
>> via my edge router.
>>
>> Two further points have been established but the exact reason for the
>> behaviour still remains a mystery
>>
>> 1/. A friend with a Pi 5 attempted to duplicate the setup, could not get
>> it to work and instead used the Network Manager  GUI to set up  a
>> (routed?) access point which worked ok. It turns out that you cannot use
>> the GUI tool to set up a bridge at all. Only nmcli.
>>
>> 2/. After a long time with traceroutes and pings I realised that this
>> particular machine was the *only one wired directly to the router via a
>> single gigabit Ethernet cable*. Everything else went via an ancient
>> 100Mbps switch that I inherited from an office clearout. In a rash of
>> 'well I tried everything else' I unplugged the Pi from the Gigabit
>> router socket  and put it into the 100Mbps switch and bingo!... Pretty
>> decent internet performance. Yes extremely long transfers sometimes
>> fail, but its very useable
>>
>> What I cannot for the life of me understand is *why*  this worked. The
>> same [Gigabit] link was involved in both local and Internet access.  The
>> only difference being that local access ALSO went through a 100Mbps switch.
>>
>> If anyone can shed light on this I would appreciate it.
>>
>> If it matters, the router is a Draytek Vigor2762Vac running PPPoE via an
>> Openrach ONT to an optical fibre for Internet and thence to the ISP.
> 
> The link-level connection involves a negotiation handshake to find
> compatible parameters. You may read up on MII (Media Independent
> Interface). When the state machines in the MII part of the MAC block in
> the Ethernet part of your SoC chip encounters an MII state machine it
> has not seen before, there may be timing dependent glitches.
> One of our customers has an installation on a remote island where
> the link between a microprocessor in his seismic gear connected via an
> ethernet switch to our radio locks up every 6 to 12 months and needs a
> remote-triggered power cycle to reset. We suggested he try another
> switch next time he can get a service tech to the island.
> 
> It is also possible that a port data rate of a Gigabit may occasionally
> cause bus contention on some internal data bus in the PI triggering
> a bus error, while 100Mbps avoids that contention. I have seen such
> bus contention cause glitches in memory controllers in a few systems
> over my career.
> 

Thank you for that.

Since the pi was always connected via the gigabit and the router 
hardware, and performed well when then routed by an external switch,  it 
seems unlikely that it was the PI<=>router link that was at fault.

I am leaning more towards the router buffering Internet data into large 
Gigabit Ethernet bursts that overwhelmed the Pi when it was forwarding 
to wifi. Limiting the data rate to 100Mbps allowed the Pis Ethernet to 
function well enough not to overload the wifi.

It was only the Internet<=>Router<=gigabit=>Pi4<=wifi=>client that broke

Without the wifi the ethernet was OK., Without the gigabit the wifi was OK.

Anyway I think we both agree that it is not something that can be 
programmed around . I will test again when I get a Pi 5 and if it still 
sucks, a wifi access point is not that expensive. The Pi is also pretty 
crippled in wifi speed.

I suspect the  PI wifi hardware was never really designed for AP usage: 
More for client access to a Wifi station.

I may try adding a wifi dongle at some point

-- 
"I guess a rattlesnake ain't risponsible fer bein' a rattlesnake, but ah 
puts mah heel on um jess the same if'n I catches him around mah chillun".



--- PyGate Linux v1.5.11
 * Origin: Dragon's Lair, PyGate NNTP<>Fido Gate (3:633/10)

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