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.

witch Ports Model SW Version SW Image Mode
------ ----- ----- ---------- ---------- ----
* 1 52 C9200L-48P-4X 17.09.04a CAT9K_LITE_IOSXE INSTALL

cm_tr_p2c_cabecera1_9300#sh etherchannel summary
Flags: D - down P - bundled in port-channel
I - stand-alone s - suspended
H - Hot-standby (LACP only)
R - Layer3 S - Layer2
U - in use f - failed to allocate aggregator

M - not in use, minimum links not met
u - unsuitable for bundling
w - waiting to be aggregated
d - default port

A - formed by Auto LAG

Number of channel-groups in use: 1
Number of aggregators: 1

Group Port-channel Protocol Ports
------+-------------+-----------+-----------------------------------------------
1 Po1(SU) PAgP Gi1/0/23(P) Gi1/0/24(P)

cm_tr_p2c_cabecera1_9300#

cm_tr_p2c_cabecera1_9300# sh int trunk

Port Mode Encapsulation Status Native vlan
Gi1/0/20 on 802.1q trunking 1
Gi1/0/21 on 802.1q trunking 1
Gi1/0/22 on 802.1q trunking 1
Te1/1/1 on 802.1q trunking 1
Po1 on 802.1q trunking 1

Port Vlans allowed on trunk
Gi1/0/20 19,32,126,132
Gi1/0/21 19,32,126,132
Gi1/0/22 19,32,126,132
Te1/1/1 310,320
Po1 19,32,126,132

Port Vlans allowed and active in management domain
Gi1/0/20 19,32,126,132
Gi1/0/21 19,32,126,132
Gi1/0/22 19,32,126,132
Te1/1/1 310,320
Po1 19,32,126,132

Port Vlans in spanning tree forwarding state and not pruned
Gi1/0/20 19,32,126,132
Gi1/0/21 19,32,126,132
Gi1/0/22 19,32,126,132
Te1/1/1 310,320
Po1 19,32,126,132
cm_tr_p2c_cabecera1_9300#

cm_tr_p2c_cabecera1_9300# sh vl br

VLAN Name Status Ports
---- -------------------------------- --------- -------------------------------
1 default active Gi1/0/1, Gi1/0/2, Gi1/0/3, Gi1/0/4, Gi1/0/5, Gi1/0/6, Gi1/0/7, Gi1/0/8, Gi1/0/9, Gi1/0/10, Gi1/0/11, Gi1/0/12
Gi1/0/13, Gi1/0/14, Gi1/0/15, Gi1/0/16, Gi1/0/17, Gi1/0/18, Gi1/0/19, Te1/1/2, Te1/1/3, Te1/1/4, Te1/1/5
Te1/1/6, Te1/1/7, Te1/1/8, Ap1/0/1
19 Admin_y_Ospf active
32 Lan1 active
126 telefonia active
132 ToIP_P2C active
310 WAN_DATOS active
320 WAN_VOZ active
400 VLAN0400 active
1002 fddi-default act/unsup
1003 token-ring-default act/unsup
1004 fddinet-default act/unsup
1005 trnet-default act/unsup
cm_tr_p2c_cabecera1_9300#

cm_tr_p2c_cabecera1_9300# sh mac add ad c85a.cfa6.c721
Mac Address Table
-------------------------------------------

Vlan Mac Address Type Ports
---- ----------- -------- -----
32 c85a.cfa6.c721 DYNAMIC Gi1/0/22
Total Mac Addresses for this criterion: 1
cm_tr_p2c_cabecera1_9300# sh mac add ad c85a.cfa6.c721
Mac Address Table
-------------------------------------------

Vlan Mac Address Type Ports
---- ----------- -------- -----
32 c85a.cfa6.c721 DYNAMIC Gi1/0/21
Total Mac Addresses for this criterion: 1
cm_tr_p2c_cabecera1_9300# sh mac add ad c85a.cfa6.c721

[M02@rt37]

Hello @matias-silva 

On 2 C9300 do that command and share output please:

show spanning-tree vlan 32

[matias-silva]

Hello,

I am attaching the commands on both C9300

cm_tr_p2c_cabecera1_9300#show spanning-tree vlan 32

VLAN0032
Spanning tree enabled protocol rstp
Root ID Priority 32
Address c47e.e094.5e00
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 32 (priority 0 sys-id-ext 32)
Address c47e.e094.5e00
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300 sec

Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Gi1/0/20 Desg FWD 20000 128.20 P2p
Gi1/0/21 Desg FWD 20000 128.21 P2p
Gi1/0/22 Desg FWD 20000 128.22 P2p
Po1 Desg FWD 10000 128.3049 P2p

cm_tr_p2c_cabecera2_9300#show spanning-tree vlan 32

VLAN0032
Spanning tree enabled protocol rstp
Root ID Priority 32
Address c47e.e094.5e00
Cost 10000
Port 3049 (Port-channel1)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 4128 (priority 4096 sys-id-ext 32)
Address c47e.e078.5380
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300 sec

Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Gi1/0/20 Desg FWD 15 128.20 P2p
Gi1/0/21 Desg FWD 15 128.21 P2p
Gi1/0/22 Desg FWD 15 128.22 P2p
Po1 Root FWD 10000 128.3049 P2p


cm_tr_p2c_cabecera2_9300#

[MHM Cisco World]

If mac flapping between g1/0/20  and any port member of PO then issue in your PO and/or  native vlan issue

MHM

[matias-silva]

It oscillates between the trunk links that go directly to the access switches, it does not oscillate within the port-channel. I have two C9300 core switches and three C9200 access switches. The C9200 have two uplinks, one connection to each C9300.

[MHM Cisco World]

There are three points to check

1- are one of port os running netflow or any monitor?

2- did you check native vlan in all your network?

3- loop that worse case 

MHM

[matias-silva]

Hello,

1- are one of port os running netflow or any monitor

 Yes, we recently implemented some configurations, I’m attaching the details

2- did you check native vlan in all your network?

Yes, it is only being used on UP ports that have no configuration and nothing connected.

3- loop that worse case 
There are no records of loops.

We recently implemented the following configurations

Cdp run
Lldp run
device-sensor filter-list dhcp list DHCP_SENSOR
option name host-name
option name client-identifier
option name client-fqdn
option name class-identifier
option name parameter-request-list
device-sensor filter-spec dhcp include list DHCP_SENSOR
device-sensor filter-list lldp list LLDP_SENSOR
tlv name system-description
tlv name port-id
tlv name system-name
tlv name system-capabilities
device-sensor filter-spec lldp include list LLDP_SENSOR
device-sensor filter-list cdp list CDP_SENSOR
tlv name device-name
tlv name capabilities-type
tlv name platform-type
tlv name version-type
device-sensor filter-spec cdp include list CDP_SENSOR
device-sensor notify all-changes
!
device-tracking tracking auto-source
device-tracking policy IPDT_POLICY
tracking enable
device-tracking tracking auto-source
interface GigabitEthernetX/X/X (puertas de acceso)
device-tracking attach-policy IPDT_POLICY
!
radius-server attribute 6 on-for-login-auth
radius-server attribute 6 support-multiple
radius-server attribute 8 include-in-access-req
radius-server attribute 25 access-request include
radius-server attribute 31 mac format ietf upper-case
radius-server attribute 31 send nas-port-detail mac-only
mac address-table notification change
mac address-table notification mac-move
epm logging
radius-server vsa send accounting
radius-server vsa send authentication
!
template MAB
dot1x timeout tx-period 10
dot1x timeout supp-timeout 10

!
flow record SW_FLOW_RECORD
description NetFlow to CTB-BECH
match ipv4 protocol
match ipv4 source address
match ipv4 destination address
match transport source-port
match transport destination-port
match interface input
collect transport tcp flags
collect interface output
collect counter bytes long
collect counter packets long
collect timestamp absolute first
collect timestamp absolute last
!
flow exporter NETFLOW_TO_CTB
description Export NetFlow to CTB-BECH
destination 172.16.xx.xx
source Vlan19
transport udp 2055
template data timeout 30
option interface-table
option application-table timeout 10
!
flow monitor IPv4_NETFLOW
record SW_FLOW_RECORD
exporter NETFLOW_TO_CTB
cache timeout active 60
cache timeout inactive 15
!
interface Gig1/0/1
ip flow monitor IPv4_NETFLOW input

!Repite para cada puerto de acceso según sea necesario.

Int vlan x ( VLAN CON DHCP)
Ip helper-address 172.16.xx.xx
Ip helper-address 172.16.xx.xx

[MHM Cisco World]

Sorry I was out

Now 

Share show spanning tree interface <interface that mac flapping between> detail 

MHM

[matias-silva]

Don't worry, I'll share the command from the C9300s. Please note that the flap log is only visible on a C9300 (Cabecera1) and not on the C9200 switches.

cm_tr_p2c_cabecera1_9300#sh spanning-tree int Gi1/0/20

Vlan Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
VLAN0019 Desg FWD 20000 128.20 P2p
VLAN0032 Desg FWD 20000 128.20 P2p
VLAN0126 Desg FWD 20000 128.20 P2p
VLAN0132 Desg FWD 20000 128.20 P2p
cm_tr_p2c_cabecera1_9300#sh spanning-tree int Gi1/0/21

Vlan Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
VLAN0019 Desg FWD 20000 128.21 P2p
VLAN0032 Desg FWD 20000 128.21 P2p
VLAN0126 Desg FWD 20000 128.21 P2p
VLAN0132 Desg FWD 20000 128.21 P2p
cm_tr_p2c_cabecera1_9300#sh spanning-tree int Gi1/0/22

Vlan Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
VLAN0019 Desg FWD 20000 128.22 P2p
VLAN0032 Desg FWD 20000 128.22 P2p
VLAN0126 Desg FWD 20000 128.22 P2p
VLAN0132 Desg FWD 20000 128.22 P2p
cm_tr_p2c_cabecera1_9300#

cm_tr_p2c_cabecera2_9300#sh spanning-tree int Gi1/0/20

Vlan Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
VLAN0019 Desg FWD 15 128.20 P2p
VLAN0032 Desg FWD 15 128.20 P2p
VLAN0126 Desg FWD 15 128.20 P2p
VLAN0132 Desg FWD 20000 128.20 P2p
cm_tr_p2c_cabecera2_9300#sh spanning-tree int Gi1/0/21

Vlan Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
VLAN0019 Desg FWD 15 128.21 P2p
VLAN0032 Desg FWD 15 128.21 P2p
VLAN0126 Desg FWD 15 128.21 P2p
VLAN0132 Desg FWD 20000 128.21 P2p
cm_tr_p2c_cabecera2_9300#sh spanning-tree int Gi1/0/22

Vlan Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
VLAN0019 Desg FWD 15 128.22 P2p
VLAN0032 Desg FWD 15 128.22 P2p
VLAN0126 Desg FWD 15 128.22 P2p
VLAN0132 Desg FWD 15 128.22 P2p

[MHM Cisco World]

Detail <<- in end of command and share output 

MHM

[matias-silva]

Ok, I'm sharing the details with you.

cm_tr_p2c_cabecera1_9300#sh spanning-tree int Gi1/0/22 de
Port 22 (GigabitEthernet1/0/22) of VLAN0019 is designated forwarding
Port path cost 20000, Port priority 128, Port Identifier 128.22.
Designated root has priority 19, address c47e.e094.5e00
Designated bridge has priority 19, address c47e.e094.5e00
Designated port id is 128.22, designated path cost 0
Timers: message age 0, forward delay 0, hold 0
Number of transitions to forwarding state: 1
Link type is point-to-point by default
BPDU: sent 2532723, received 10

Port 22 (GigabitEthernet1/0/22) of VLAN0032 is designated forwarding
Port path cost 20000, Port priority 128, Port Identifier 128.22.
Designated root has priority 32, address c47e.e094.5e00
Designated bridge has priority 32, address c47e.e094.5e00
Designated port id is 128.22, designated path cost 0
Timers: message age 0, forward delay 0, hold 0
Number of transitions to forwarding state: 1
Link type is point-to-point by default
BPDU: sent 2532723, received 9

Port 22 (GigabitEthernet1/0/22) of VLAN0126 is designated forwarding
Port path cost 20000, Port priority 128, Port Identifier 128.22.
Designated root has priority 126, address c47e.e094.5e00
Designated bridge has priority 126, address c47e.e094.5e00
Designated port id is 128.22, designated path cost 0
Timers: message age 0, forward delay 0, hold 0
Number of transitions to forwarding state: 1
Link type is point-to-point by default
BPDU: sent 2532722, received 0

Port 22 (GigabitEthernet1/0/22) of VLAN0132 is designated forwarding
Port path cost 20000, Port priority 128, Port Identifier 128.22.
Designated root has priority 132, address c47e.e094.5e00
Designated bridge has priority 132, address c47e.e094.5e00
Designated port id is 128.22, designated path cost 0
Timers: message age 0, forward delay 0, hold 0
Number of transitions to forwarding state: 1
Link type is point-to-point by default
BPDU: sent 2532723, received 9
cm_tr_p2c_cabecera1_9300#sh spanning-tree int Gi1/0/20 de
Port 20 (GigabitEthernet1/0/20) of VLAN0019 is designated forwarding
Port path cost 20000, Port priority 128, Port Identifier 128.20.
Designated root has priority 19, address c47e.e094.5e00
Designated bridge has priority 19, address c47e.e094.5e00
Designated port id is 128.20, designated path cost 0
Timers: message age 0, forward delay 0, hold 0
Number of transitions to forwarding state: 1
Link type is point-to-point by default
BPDU: sent 2532728, received 13

Port 20 (GigabitEthernet1/0/20) of VLAN0032 is designated forwarding
Port path cost 20000, Port priority 128, Port Identifier 128.20.
Designated root has priority 32, address c47e.e094.5e00
Designated bridge has priority 32, address c47e.e094.5e00
Designated port id is 128.20, designated path cost 0
Timers: message age 0, forward delay 0, hold 0
Number of transitions to forwarding state: 1
Link type is point-to-point by default
BPDU: sent 2532728, received 13

Port 20 (GigabitEthernet1/0/20) of VLAN0126 is designated forwarding
Port path cost 20000, Port priority 128, Port Identifier 128.20.
Designated root has priority 126, address c47e.e094.5e00
Designated bridge has priority 126, address c47e.e094.5e00
Designated port id is 128.20, designated path cost 0
Timers: message age 0, forward delay 0, hold 0
Number of transitions to forwarding state: 1
Link type is point-to-point by default
BPDU: sent 2532728, received 0

Port 20 (GigabitEthernet1/0/20) of VLAN0132 is designated forwarding
Port path cost 20000, Port priority 128, Port Identifier 128.20.
Designated root has priority 132, address c47e.e094.5e00
Designated bridge has priority 132, address c47e.e094.5e00
Designated port id is 128.20, designated path cost 0
Timers: message age 0, forward delay 0, hold 0
Number of transitions to forwarding state: 1
Link type is point-to-point by default
BPDU: sent 2532728, received 13
cm_tr_p2c_cabecera1_9300#sh spanning-tree int Gi1/0/21 de
Port 21 (GigabitEthernet1/0/21) of VLAN0019 is designated forwarding
Port path cost 20000, Port priority 128, Port Identifier 128.21.
Designated root has priority 19, address c47e.e094.5e00
Designated bridge has priority 19, address c47e.e094.5e00
Designated port id is 128.21, designated path cost 0
Timers: message age 0, forward delay 0, hold 0
Number of transitions to forwarding state: 1
Link type is point-to-point by default
BPDU: sent 2532732, received 9

Port 21 (GigabitEthernet1/0/21) of VLAN0032 is designated forwarding
Port path cost 20000, Port priority 128, Port Identifier 128.21.
Designated root has priority 32, address c47e.e094.5e00
Designated bridge has priority 32, address c47e.e094.5e00
Designated port id is 128.21, designated path cost 0
Timers: message age 0, forward delay 0, hold 0
Number of transitions to forwarding state: 1
Link type is point-to-point by default
BPDU: sent 2532732, received 9

Port 21 (GigabitEthernet1/0/21) of VLAN0126 is designated forwarding
Port path cost 20000, Port priority 128, Port Identifier 128.21.
Designated root has priority 126, address c47e.e094.5e00
Designated bridge has priority 126, address c47e.e094.5e00
Designated port id is 128.21, designated path cost 0
Timers: message age 0, forward delay 0, hold 0
Number of transitions to forwarding state: 1
Link type is point-to-point by default
BPDU: sent 2532731, received 0

Port 21 (GigabitEthernet1/0/21) of VLAN0132 is designated forwarding
Port path cost 20000, Port priority 128, Port Identifier 128.21.
Designated root has priority 132, address c47e.e094.5e00
Designated bridge has priority 132, address c47e.e094.5e00
Designated port id is 128.21, designated path cost 0
Timers: message age 0, forward delay 0, hold 0
Number of transitions to forwarding state: 1
Link type is point-to-point by default
BPDU: sent 2532732, received 9

cm_tr_p2c_cabecera2_9300#sh spanning-tree int Gi1/0/20 de
Port 20 (GigabitEthernet1/0/20) of VLAN0019 is designated forwarding
Port path cost 15, Port priority 128, Port Identifier 128.20.
Designated root has priority 19, address c47e.e094.5e00
Designated bridge has priority 4115, address c47e.e078.5380
Designated port id is 128.20, designated path cost 10000
Timers: message age 0, forward delay 0, hold 0
Number of transitions to forwarding state: 3
Link type is point-to-point by default
BPDU: sent 2532765, received 14

Port 20 (GigabitEthernet1/0/20) of VLAN0032 is designated forwarding
Port path cost 15, Port priority 128, Port Identifier 128.20.
Designated root has priority 32, address c47e.e094.5e00
Designated bridge has priority 4128, address c47e.e078.5380
Designated port id is 128.20, designated path cost 10000
Timers: message age 0, forward delay 0, hold 0
Number of transitions to forwarding state: 3
Link type is point-to-point by default
BPDU: sent 2532763, received 14

Port 20 (GigabitEthernet1/0/20) of VLAN0126 is designated forwarding
Port path cost 15, Port priority 128, Port Identifier 128.20.
Designated root has priority 126, address c47e.e094.5e00
Designated bridge has priority 4222, address c47e.e078.5380
Designated port id is 128.20, designated path cost 10000
Timers: message age 0, forward delay 0, hold 0
Number of transitions to forwarding state: 3
Link type is point-to-point by default
BPDU: sent 2532759, received 0

Port 20 (GigabitEthernet1/0/20) of VLAN0132 is designated forwarding
Port path cost 20000, Port priority 128, Port Identifier 128.20.
Designated root has priority 132, address c47e.e094.5e00
Designated bridge has priority 4228, address c47e.e078.5380
Designated port id is 128.20, designated path cost 10000
Timers: message age 0, forward delay 0, hold 0
Number of transitions to forwarding state: 3
Link type is point-to-point by default
BPDU: sent 2532759, received 14
cm_tr_p2c_cabecera2_9300#sh spanning-tree int Gi1/0/21 de
Port 21 (GigabitEthernet1/0/21) of VLAN0019 is designated forwarding
Port path cost 15, Port priority 128, Port Identifier 128.21.
Designated root has priority 19, address c47e.e094.5e00
Designated bridge has priority 4115, address c47e.e078.5380
Designated port id is 128.21, designated path cost 10000
Timers: message age 0, forward delay 0, hold 0
Number of transitions to forwarding state: 3
Link type is point-to-point by default
BPDU: sent 2532765, received 14

Port 21 (GigabitEthernet1/0/21) of VLAN0032 is designated forwarding
Port path cost 15, Port priority 128, Port Identifier 128.21.
Designated root has priority 32, address c47e.e094.5e00
Designated bridge has priority 4128, address c47e.e078.5380
Designated port id is 128.21, designated path cost 10000
Timers: message age 0, forward delay 0, hold 0
Number of transitions to forwarding state: 3
Link type is point-to-point by default
BPDU: sent 2532763, received 12

Port 21 (GigabitEthernet1/0/21) of VLAN0126 is designated forwarding
Port path cost 15, Port priority 128, Port Identifier 128.21.
Designated root has priority 126, address c47e.e094.5e00
Designated bridge has priority 4222, address c47e.e078.5380
Designated port id is 128.21, designated path cost 10000
Timers: message age 0, forward delay 0, hold 0
Number of transitions to forwarding state: 3
Link type is point-to-point by default
BPDU: sent 2532761, received 0

Port 21 (GigabitEthernet1/0/21) of VLAN0132 is designated forwarding
Port path cost 20000, Port priority 128, Port Identifier 128.21.
Designated root has priority 132, address c47e.e094.5e00
Designated bridge has priority 4228, address c47e.e078.5380
Designated port id is 128.21, designated path cost 10000
Timers: message age 0, forward delay 0, hold 0
Number of transitions to forwarding state: 3
Link type is point-to-point by default
BPDU: sent 2532763, received 12
cm_tr_p2c_cabecera2_9300#sh spanning-tree int Gi1/0/22 de
Port 22 (GigabitEthernet1/0/22) of VLAN0019 is designated forwarding
Port path cost 15, Port priority 128, Port Identifier 128.22.
Designated root has priority 19, address c47e.e094.5e00
Designated bridge has priority 4115, address c47e.e078.5380
Designated port id is 128.22, designated path cost 10000
Timers: message age 0, forward delay 0, hold 0
Number of transitions to forwarding state: 3
Link type is point-to-point by default
BPDU: sent 2532765, received 11

Port 22 (GigabitEthernet1/0/22) of VLAN0032 is designated forwarding
Port path cost 15, Port priority 128, Port Identifier 128.22.
Designated root has priority 32, address c47e.e094.5e00
Designated bridge has priority 4128, address c47e.e078.5380
Designated port id is 128.22, designated path cost 10000
Timers: message age 0, forward delay 0, hold 0
Number of transitions to forwarding state: 3
Link type is point-to-point by default
BPDU: sent 2532763, received 13

Port 22 (GigabitEthernet1/0/22) of VLAN0126 is designated forwarding
Port path cost 15, Port priority 128, Port Identifier 128.22.
Designated root has priority 126, address c47e.e094.5e00
Designated bridge has priority 4222, address c47e.e078.5380
Designated port id is 128.22, designated path cost 10000
Timers: message age 0, forward delay 0, hold 0
Number of transitions to forwarding state: 3
Link type is point-to-point by default
BPDU: sent 2532762, received 0

Port 22 (GigabitEthernet1/0/22) of VLAN0132 is designated forwarding
Port path cost 15, Port priority 128, Port Identifier 128.22.
Designated root has priority 132, address c47e.e094.5e00
Designated bridge has priority 4228, address c47e.e078.5380
Designated port id is 128.22, designated path cost 10000
Timers: message age 0, forward delay 0, hold 0
Number of transitions to forwarding state: 4
Link type is point-to-point by default
BPDU: sent 2532768, received 14

[MHM Cisco World]

VLAN 126 the SW is 0 received any bpdu 

And port g1/0/22 or 21 are trunk 

So there is issue with vlan 126.

Vlan 32 and 126 is native vlan in any SW?

Check STP of vlan 126 if you use RSTP 

If you use different mode of STP please inform me which mode ypu use 

MHM

[matias-silva]

VLAN 126 was not in use and had no configuration, so we removed it at both layer 2 and layer 3. VLAN 32 is the data VLAN for the access ports on each switch.

Despite having removed the VLAN from the configurations, the flapping persists on the cabecera 1 (C9300)

[matias-silva]

I have another network with the same configurations, and it works correctly. The only difference is that on those switches, the version is 17.06.04, and on the ones with the flapping issue, the version is 17.09.04a. Could there be a bug in C9200?

[MHM Cisco World]

Port 22 (GigabitEthernet1/0/22) of VLAN0126 is designated forwarding
Port path cost 15, Port priority 128, Port Identifier 128.22.
Designated root has priority 126, address c47e.e094.5e00
Designated bridge has priority 4222, address c47e.e078.5380
Designated port id is 128.22, designated path cost 10000
Timers: message age 0, forward delay 0, hold 0
Number of transitions to forwarding state: 3
Link type is point-to-point by default
BPDU: sent 2532762, received 0 <<<- run same command of show spanning tree interface detail and check this count is it increase or still same

Also make double check 

Vlan 32 is native vlan in any trunk

Vlan 126 is totally remove from SW 

Any SW run old STP mode or MST not PVST

MHM