Community,
I am facing a very interesting and strange Topology Change issue with Rapid spanning tree. Here is what I am noticing.
On the Catalyst 9300-48P (17.6.3), I am seeing some port flapping on ports connected to AP's. These ports are configured with portfast as shown:
interface GigabitEthernet1/0/47
description TO0047-AP59
switchport access vlan 20
switchport trunk native vlan 255
switchport trunk allowed vlan 255,401-403
switchport mode trunk
switchport voice vlan 110
spanning-tree portfast
spanning-tree bpduguard enable
end
However, when this port goes down and then back up, Spanning tree is generating a TC for it as shown below:
SW03#show spanning-tree vlan 401 detail
VLAN0401 is executing the rstp compatible Spanning Tree protocol
Bridge Identifier has priority 32768, sysid 401, address a4b2.3993.d180
Configured hello time 2, max age 20, forward delay 15, transmit hold-count 6
Current root has priority 33169, address 084f.a9e5.1c80
Root port is 3049 (Port-channel1), cost of root path is 30000
Topology change flag set, detected flag not set
Number of topology changes 27075 last change occurred 00:00:16 ago
from GigabitEthernet1/0/47
Times: hold 1, topology change 35, notification 2
hello 2, max age 20, forward delay 15
Timers: hello 0, topology change 19, notification 0, aging 300
As you can see this is happening alot, not on just this port, but in several places in my network.
What I dont understand is why RSTP is genertaing a TC for ports that are clearly supposed to be in an Edge Status (from portfast). According to everything ive ever read, RSTP should only gen a TC when a NON-EDGE Designated port goes to forwarding.
I have not yet got to the bottom of the port flaps, but suffice to say these TCs are causing a lot of MAC Flushes and Relearning and it maybe contributing to connectivity issues being reported.
Thanks for any help you can provide.
