[External] [c-nsp] N9K traffic lost when redundant link comes up

[Hunter Fuller]

I am sorry, I misread your message. I thought they were in one bundle, but
you said you  made another bundle. My apologies.

--
Hunter Fuller (they)
Router Jockey
VBH Annex B-5
+1 256 824 5331

Office of Information Technology
The University of Alabama in Huntsville
Network Engineering


On Tue, Mar 9, 2021 at 11:20 AM Hunter Fuller <hf0002 at uah.edu> wrote:

> If you are just adding a port to a Port-channel, the box should not see
> any MAC "moves" as such. The MAC is learned on the Port-channel interface
> no matter which bundle member it uses.
>
> This is going to be something more esoteric, or a bug.
>
> --
> Hunter Fuller (they)
> Router Jockey
> VBH Annex B-5
> +1 256 824 5331
>
> Office of Information Technology
> The University of Alabama in Huntsville
> Network Engineering
>
>
> On Tue, Mar 9, 2021 at 11:10 AM <cnsp at marenda.net> wrote:
>
>>
>> Hi,
>>
>> i have a pair of N9K-C93180YC-EX running nxos.9.3.1.bin connected with a
>> LACP port-channel (pair of 100G Links).
>> I got a pair of N9K-C9348GC-FXP running nxos.9.3.5.bin connect with a
>> (single-100G Link) LACP post-channel to only one of the above switches.
>>
>> I finally got more transceivers to create the missing redundant link(s)
>> to the other one of the first switches ,
>> In a second LACP port-channel with just one single-100G Link.
>>
>> No Multi-Chassis LACP here, each device works stand-alone,
>> spanning tree mode is MST, everywhere identically configured.
>>
>> Expected behaviour is:
>> New link gets active, and
>> if spanning tree finds this new link as "lower" it would block it.
>> if spanning tree finds it "better" it should start to use it and block
>> somewhere else.
>>
>> But monitoring was crying, and I found in the loggin:
>> 16:30:19 dsw2 %L2FM-2-L2FM_MAC_FLAP_DISABLE_LEARN: Disabling learning in
>> vlan XXX for 120s due to too many mac moves
>> 16:32:19 dsw2 %L2FM-2-L2FM_MAC_FLAP_RE_ENABLE_LEARN: Re-enabling learning
>> in vlan XXX
>>
>> Yes, that was also the duration of the "outage", adding a redundant link
>> leads two two minutes outage ☹
>>
>> Cisco's error-messages finder tells me that there is nothing to do  ?!?
>>
>> Case opened, infos submitted, but two days (plus weekend) silence.
>>
>> Any idea what is happening and how I can avoid that (the fourth link
>> wants to be plugged in).
>>
>> Will that happen when a link fails, STP unblocks an other link and
>> therefor the switch relearns too much mac-addresses too fast
>>
>> so I get again 2 minutes "down" instead of just 2..3 seconds ?
>>
>> The ancient C4900M did not show that behaviour...
>>
>> Any suggestions?
>>
>> Thank you for your patience,
>>
>> Jürgen.
>>
>>
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>