[PLUG] Lan loops - follow on PoE injecto

Russell Senior russell at personaltelco.net
Fri Dec 27 00:13:04 UTC 2019


For reference, this is what the full-blown output of "swconfig dev switch0
show" from the MT7621 looks like:

  http://sprunge.us/YPQwYE

On Thu, Dec 26, 2019 at 4:07 PM Russell Senior <russell at personaltelco.net>
wrote:

>
>
> On Thu, Dec 26, 2019 at 3:54 PM Russell Senior <russell at personaltelco.net>
> wrote:
>
>> Ooh, try this: shell in and run: swconfig dev switch0 show | grep port
>>
>> Connect your loop and run it again.
>>
>> Then, seeing which port link state changed, you'll know what switch ports
>> are LAN1 and LAN2. Piping to less instead of grep should give you a bunch
>> of port stats.
>>
>
> It might not give as verbose of port stats as I suggested. The swconfig
> output for my "Atheros AR8316 rev. 1 switch" isn't nearly as verbose as the
> one in my mediatek MT7621-based router. But I don't have yours, so I don't
> know for sure.
>
>
>> Ping an address in the br-lan network space, and try it again.
>>
>> On Thu, Dec 26, 2019 at 3:42 PM Tomas Kuchta <
>> tomas.kuchta.lists at gmail.com> wrote:
>>
>>> Qualcomm QCA9563 SOC in GL-AR750S package.
>>>
>>>
>>>
>>> On Fri, Dec 27, 2019, 00:12 Mike C. <mconnors1 at gmail.com> wrote:
>>>
>>> > I have a theory about why it didn't work on your device. Its what I
>>> > expected would happen and why I didn't suggest what Russell did to just
>>> > loop one LAN port to another. I think its due to the architecture.
>>> >
>>> > What make and model is your switch/router?
>>> >
>>> > On Thu, Dec 26, 2019, 2:24 PM <tomas.kuchta.lists at gmail.com> wrote:
>>> >
>>> > > It seems that in my case - looping LAN1 with LAN2 and
>>> sending/receiving
>>> > > WAN<-->WLAN3 traffic leads to no visible traffic degradation. That
>>> > > probably mean
>>> > > that I failed to create lan loop.
>>> > >
>>> > > The lights were "kind of" busy on LAN1 <--> LAN2, but the wlan3 and
>>> > > upstream WAN
>>> > > are slow enough to observe any effect on that traffic.
>>> > >
>>> > > I will try to gather together 8+ switches when I get home after the
>>> New
>>> > > Year.
>>> > > With that I may be able to observe some traffic pattern change when
>>> > > crossing
>>> > > switching depth 7.
>>> > >
>>> > > > The router/switch looks this way:
>>> > > > - WAN (eth0)
>>> > > >     +- LAN1 (eth1)
>>> > > >     +- LAN2 (eth2)
>>> > > >     +- WLAN3 (wlan0)
>>> > > > The router is running openWrt.
>>> > > >
>>> > >
>>> > > Tomas
>>> > >
>>> > > On Wed, 2019-12-25 at 09:15 -0800, Mike C. wrote:
>>> > > > >
>>> > > > > I happened to have a netgear FS105 nearby. Plugging in a laptop
>>> to a
>>> > > switch
>>> > > > > port, and plugging a patch cable between two other switch ports
>>> and
>>> > > pinging
>>> > > > > a random ip address from the laptop set off the broadcast storm.
>>> > > Running
>>> > > > > tcpdump from the laptop showed a bunch of "MPCP, Opcode Pause,
>>> length
>>> > > 46"
>>> > > > > packets. Unplugging the loop, the packets stop immediately.
>>> > > > >
>>> > > >
>>> > > > The reason this works and why I suspect it won't work on the OPs
>>> router
>>> > > is
>>> > > > the Netgear isn't a 802.1D (Spanning Tree Compliant) switch. Those
>>> > > > multicast packets are flow control packets and would not be
>>> forwarded
>>> > out
>>> > > > all switch ports downstream as per 802.1D they're reserved to be
>>> acted
>>> > > upon
>>> > > > only by the switch.
>>> > > > _______________________________________________
>>> > > > PLUG mailing list
>>> > > > PLUG at pdxlinux.org
>>> > > > http://lists.pdxlinux.org/mailman/listinfo/plug
>>> > > _______________________________________________
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>>> > > PLUG at pdxlinux.org
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>>> > >
>>> > _______________________________________________
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>>> >
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>>



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