Spanning Tree Protocol Failover And Failback Observations; Lab Environment; Figure 3. Topology Diagram: Stp Interoperability Observations Lab - Dell Force10 C150 Manual

Deploying the Dell Force10 MXL into a Cisco Nexus Network Environment

Spanning Tree Protocol Failover and Failback Observations

The primary role of any Spanning Tree Protocol is to prevent loops from occurring in a network
topology. The secondary role is to re-converge after a topology change (link failure) as quickly as
possible. The Force10 MXL blade switch supports Spanning Tree Protocol (IEEE 802.1d), Rapid Spanning
Tree Protocol (802.1w), Multiple Spanning Tree Protocol (IEEE 802.1s) and Per VLAN Spanning Tree
Protocol. Some observations regarding the interoperability of Nexus switches and the Force10 MXL
blade switch using spanning-tree protocols are presented below. Figure 3 depicts the switch
configuration used during these observations.
Figure 3. Topology Diagram: STP Interoperability Observations Lab
Ping Source
Root Bridge
192.168.0.61 VLAN 10
P 1 / 25
Nexus Nexus
N5K1 N5K2
Primary
Ping Path
Failover
P 1 / 5
Ping Path
Shortest Path
Cost
P 1 / 45 P 1 / 43
Force10
MXL2
Ping Destination
192.168.0.42 VLAN 10

Lab Environment

The configuration is composed of two Nexus switches. Nexus switches can run in 2 STP modes, either
MSTP or Rapid PVST+. The behavior of both modes was observed. A single Force10 MXL blade switch
was used in the configuration.
Please note: The 2 Nexus switches used for the STP observations were not the same as the ones used
earlier in this document and as a result have different MAC addresses etc.
Cisco's vPC was not used in the configuration. If vPC had been configured on the Nexus downlink ports
to the Force10 MXL blade switch, then there would have been a preference to have a LAG configured
on the two MXL ports so that both links could be used in an Active-Active LACP scenario. In that case,
when spanning tree information is observed from the Force10 MXL blade switch's perspective, the Port
Channel's role would be Root, but since there is only one logical path (the port channel) there would
be no interface designated as an Alternate. By not using vPC, a triangle of 3 independent switches was
created and STP was forced to block at least one of the Force10 MXL blade switch links in order to
guarantee a loop free topology.
In the configuration for this lab, the N5K1 was configured as the Root Bridge Primary and the N5K2 was
configured as the Root Bridge Secondary. Since N5K1 was the Root Bridge, the link between it and the
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