SW_MATM-4-MACFLAP_NOTIF flapping between port Gi1/0/21 and port Gi1/0/

[matias-silva]

I am experiencing flap issues on my Cisco 9300 devices. These are connected to 9200 access switches, creating redundancy with two core switches (9300). The access switches have two uplink ports, one connected to each core switch. I have reviewed the spanning-tree, port-channel, and trunk configurations and have not detected any inconsistencies. All devices are provisioned in DNA Center.

When executing a show mac address for the MAC, it is observed that it oscillates between ports 21 and 22. I also checked for multiple MAC addresses on an access port to identify any out-of-standard switches, but nothing was found. No physical loop was detected either.

[matias-silva]

sh spanning-tree summary

[Jose Suarez]

Hi, 

Did you verify that all the switch were using the same STP(RSTP or rapid-pvst)?

Could you share the "show spanning-tree summary" of the access router too?

Best Regards

[matias-silva]

sh spanning-tree summary

[MHM Cisco World]

Root bridge for: VLAN0001, VLAN0310, VLAN0320 <<- SW9300-2
Root bridge for: VLAN0001, VLAN0019, VLAN0032, VLAN0132, VLAN0310, VLAN0320 <<-SW9300-1
This not same share you provide before 
sure this STP issue 

[matias-silva]

I don’t have VLANs 310 and 320 configured in the spanning tree; those VLANs are used for the WAN.

[matias-silva]

sh run | sec spanning-tree

[MHM Cisco World]

It new Little clear

First wait @Jose Suarez reply 

For me 

1- you run guard root in both SW ? In which interface ?

2- you not allow vlan1 in any trunk?? Which is native of all trunk?

3- you dont allow vlan 310 and 320 in PO between two 9300 SW?

MHM

[matias-silva]

OK thanks,

1- you run guard root in both SW ? In which interface ?
Yes, I configured guard root on both switches on interfaces g1/0/20, g1/0/21, and g1/0/22, which are connected to the C9200s.
2- you not allow vlan1 in any trunk?? Which is native of all trunk?
I do not allow VLAN 1 on any trunk.

[MHM Cisco World]

Then return to me first reply' it issue of native vlan.

Now what you need 

1- check cost' I mention I see cost 15 why that ? As I see you use cost method long 

2- are ypu sure native is 32 in all trunk' I see in some of output ypu share the native was vlan 1

3- allow vlan 1' it already by defualt in all SW so make pvst send bpdu and close any loop of this vlan

Thanks a lot

MHM

[matias-silva]

sh spanning-tree int g1/0/20 de

[Jose Suarez]

Hi,

It looks like there might be a mismatch with the native VLANs between the switches ,the 9300 has VLAN 1 as native, and it seems like the access switches are using VLAN 32. Could you share the outputs of show interfaces trunk and show vlan brief from both the access and core switches? 

That way we can confirm and clear up any doubts

Regards,

[matias-silva]

show int trunk

Port Mode Encapsulation Status Native vlan
Gi1/0/47 on 802.1q trunking 1
Gi1/0/48 on 802.1q trunking 1

[MHM Cisco World]

Please make sure vlan 32 is native in core Sw and access SW 

You can not set native in core vlan1 and in access SW vlan 32

MHM

[matias-silva]

Upon closer review, I noticed that VLAN 1 appears as the native VLAN on all devices, and I don’t have any configuration related to the native VLAN.

[MHM Cisco World]

please check note in red color