MST maps multiple VLANs to an instance, which reduces the number of spanning tree instances. Rapid-PVST+ creates an instance for each VLAN. In this example, each Cisco N5K is a root for VLAN 10 and VLAN 20 with the other acting as secondary.
Test steps
- 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 switch and measure traffic loss and duration of traffic loss.
- Recover e1/1/9 on S4128-SW1 and measure traffic loss and duration of traffic loss.
Results
For VLAN 1, both the switches interoperate and agreed on the root bridge. For VLANs 10 and 20, Dell EMC and Cisco switches saw themselves as root and did not interoperate. The different port roles on Dell EMC switch are shown in the MSTI 0 and MSTI 1 on S4128-SW1 example below. Ports, e1/1/9 and e1/1/8 on S4128-SW1 will be elected as Master and alternate ports since e1/1/9 is the non-blocking boundary port connected to CIST (Common and Internal Spanning Tree) root when Cisco N5K1 is the root bridge for VLAN 1.
N5K1# show spanning-tree
VLAN0001
Spanning tree enabled protocol rstp
Root ID Priority 24577
Address 547f.eeac.13c1
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 24577 (priority 24576 sys-id-ext 1)
Address 547f.eeac.13c1
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Interface Role Sts Cost Prio.Nbr Type
--------- ---- --- ---- ------------ -------
Eth1/3 Desg FWD 2 128.131 Edge P2p
Eth1/30 Desg FWD 2 128.158 P2p
Eth1/31 Desg FWD 2 128.159 P2p
VLAN0010
Spanning tree enabled protocol rstp
Root ID Priority 24586
Address 547f.eeac.13c1
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 24586 (priority 24576 sys-id-ext 10)
Address 547f.eeac.13c1
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Interface Role Sts Cost Prio.Nbr Type
--------- ---- -------- -------- --------
Eth1/3 Desg FWD 2 128.131 Edge P2p
Eth1/30 Desg FWD 2 128.158 P2p
Eth1/31 Desg FWD 2 128.159 P2p
S4128-SW1# show spanning-tree active
Spanning tree enabled protocol msti with force-version mst
MSTI 0 VLANs mapped 1-9,11-19,21-4093
Executing IEEE compatible Spanning Tree Protocol
Root ID Priority 24577, Address 547f.eeac.13c1
Root Bridge hello time 2, max age 20, forward delay 15, max hops 20
Bridge ID Priority 32768, Address f48e.385f.3dca
Configured hello time 2, max age 20, forward delay 15, max hops 20
CIST regional root ID Priority 32768, Address f48e.385f.3dca
CIST external path cost 2000
Name PortID Prio Cost Sts Cost BridgeID PortID
--------------------------------------------------------------------------
ethernet1/1/3 128.524 128 2000 FWD 2000 32768 f48e.385f.3dca 128.524
ethernet1/1/8 128.544 128 2000 BLK 2 32769 002a.6a0d.a17c 128.156
ethernet1/1/9 128.548 128 2000 FWD 0 24577 547f.eeac.13c1 128.158
Interface
Name Role PortID Prio Cost Sts Cost Link-type Edge
--------------------------------------------------------------------------
ethernet1/1/3 Desg 128.524 128 2000 FWD 2000 AUTO No
ethernet1/1/8 Altr 128.544 128 2000 BLK 2 AUTO No
ethernet1/1/9 Root 128.548 128 2000 FWD 0 AUTO No
MSTI 1 VLANs mapped 10
Executing IEEE compatible Spanning Tree Protocol
Root ID Priority 32768, Address f48e.385f.3dca
Root Bridge hello time 2, max age 20, forward delay 15, max hops 20
Bridge ID Priority 32768, Address f48e.385f.3dca
We are the root of MSTI 1
Configured hello time 2, max age 20, forward delay 15, max hops 20
CIST regional root ID Priority 0, Address 0023.00ed.0700
CIST external path cost 0
Interface
Name PortID Prio Cost Sts Cost BridgeID PortID
----------------------------------------------------------------------------
ethernet1/1/3 128.524 128 2000 FWD 0 32768 f48e.385f.3dca 128.524
ethernet1/1/8 128.544 128 2000 BLK 0 32768 f48e.385f.3dca 128.544
ethernet1/1/9 128.548 128 2000 FWD 0 32768 f48e.385f.3dca 128.548
Name Role PortID Prio Cost Sts Cost Link-type Edge
---------------------------------------------------------------
ethernet1/1/3 Desg 128.524 128 2000 FWD 0 AUTO No
ethernet1/1/8 Altr 128.544 128 2000 BLK 0 AUTO No
ethernet1/1/9 Master 128.548 128 2000 FWD 0 AUTO No