Symptom
- Spanning will create instance on interface that is a part of a port-channel
- This will cause STP disputes on the root bridge.
Conditions
- N3k
- Configuring the interface and port-channel in this order:
interface port-channel11 ; switchport mode trunk
interface port-channel11 ; switchport trunk allowed vlan 802
interface port-channel11 ; mtu 9216
int eth 1/43
switchport mode trunk
channel-group 11 force mode active <<<<<<<<<< the trigger.
Workaround
Use "channel-group" without force option i.e. Configure MTU explicitly on Eth1/43 before running 'channel-group'
Further Problem Description
- Spanning will create instance on interface that is a part of a port-channel
- This will cause STP disputes on the root bridge.
interface Ethernet1/43
switchport mode trunk
switchport trunk allowed vlan 802
mtu 9216
channel-group 11 mode active
MOWER-N3k2# show spanning-tree vlan 801
VLAN0801
Spanning tree enabled protocol rstp
Root ID Priority 33569
Address 0062.ec40.4f07
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 33569 (priority 32768 sys-id-ext 801)
Address 0062.ec40.4f07
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Interface Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Eth1/43 Desg FWD 4 128.169 P2p <<<<<<<<<<<<<<<
