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OPERATIONAL DEFECT DATABASE
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Multiple Symptoms may be seen such as below: 1) STP disputes on a downstream STP Root switch that is connected to vPC pair using fabric-peering. 2) show spanning-tree detail command on the Nexus doesn't increment for the "received" BPDU Counter stats 3) Ethanalyzer on Nexus 9k shows the incoming STP BPDUs with the correct dot1q tag and with Root information(includes better priority for the Vlan in Question) Example: Nexus Leaf-1 is claiming root: Leaf-1(config)# show spanning-tree vlan 200 VLAN0200 Spanning tree enabled protocol rstp Root ID Priority 32968 Address 7c21.0e5f.041f This bridge is the root Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Bridge ID Priority 32968 (priority 32768 sys-id-ext 200) Address 7c21.0e5f.041f Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Interface Role Sts Cost Prio.Nbr Type ---------------- ---- --- --------- -------- -------------------------------- Po10 Desg FWD 4 128.4105 (vPC peer-link) Network P2p Po200 Desg FWD 1 128.4295 (vPC) P2p However it is receiving superior BPDU's and ignoring them: Leaf-1(config)# ethanalyzer local interface inband display-filter "vlan.id==200 && stp" limit-c 0 Capturing on inband 2022-04-14 23:19:22.165540 00:26:f0:c8:00:00 -> 01:00:0c:cc:cc:cd STP RST. Root= 32768/200/7c:21:0e:5f:04:1f Cost = 0 Port = 0x90c7 2022-04-14 23:19:22.489421 00:23:5e:a5:30:80 -> 01:00:0c:cc:cc:cd STP RST. Root= 32768/200/00:23:5e:a5:30:80 Cost = 0 Port = 0x82b0 >> Incoming Superior BPDUs from downstream switch 2022-04-14 23:19:24.165780 00:26:f0:c8:00:00 -> 01:00:0c:cc:cc:cd STP RST. Root= 32768/200/7c:21:0e:5f:04:1f Cost = 0 Port = 0x90c7 2022-04-14 23:19:24.489506 00:23:5e:a5:30:80 -> 01:00:0c:cc:cc:cd STP RST. Root= 32768/200/00:23:5e:a5:30:80 Cost = 0 Port = 0x82b0 Meanwhile downstream switch is in dispute (as it has the superior/lower bridge-id) Client_Switch#show spanning-tree vlan 200 VLAN0200 Spanning tree enabled protocol rstp Root ID Priority 32968 Address 0023.5ea5.3080 This bridge is the root Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Bridge ID Priority 32968 (priority 32768 sys-id-ext 200) Address 0023.5ea5.3080 Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Aging Time 300 sec Interface Role Sts Cost Prio.Nbr Type ------------------- ---- --- --------- -------- -------------------------------- Po48 Desg BLK 1 128.1328 P2p Dispute
Nexus 9000 running 9.3(7) or 9.3(9) with below conditions Fabric peering configured, and a link is brought up toward a single VPC peer. E.g., if N9k1 and N9k2 are vPC Fabric Peering Switches, the downstream vPC is up to only N9k1. N9k2 has the vPC configured, but not operationally up. OR Reload with link being up toward both peers
Shutting down the vpc domain although this is an intrusive step as all downstream vPC port-channels will go down on this step. A reload may NOT correct this behavior.
During Migration from legacy to VXLAN Fabric, it may be needed to configure or place the STP root for Vlans on the legacy environment. The issue documented in this Defect applies when the STP Root is on the legacy network connected to the VXLAN Leaf switches that are in Fabric Peering mode.