The following figure depicts the physical and logical network topology with traffic flow at a steady state. Each Cisco N5K is a root for VLAN 10 and VLAN 20 respectively with the other acting as secondary. VLAN 10 is forwarded on port 9 and blocked on port 8 and vice versa for VLAN 20. This is the normal behavior of having different spanning tree instances for each VLAN.
The following figure shows the port status and port roles for VLAN 20 on S4128-SW1.
Test steps
The following test steps were conducted using Ixia IxExplorer to simulate a fail-over scenario:
- Create two tagged streams of VLAN ID 10 and 20 with source port 3 and destination ports 1 and 2.
- Shut down e1/1/9 on S4128-SW1 to simulate a fail-over scenario and check for any traffic disruption.
- Recover e1/1/9 on S4128-SW1 and check for any traffic disruption and ensure N5K1 becomes the root.
- Repeat steps 2 and 3 for e1/1/8 on the S4128-SW1 switch.
Results
In RPVST+, different per-VLAN spanning tree instances were created. Traffic converges in both the RPVST+ instances 10 and 20. The blocked VLANs started to forward traffic right away upon a link failure. Both spanning tree modes use the same convergence timers, therefore convergence times upon link failures are quick as expected.