Dell SmartFabric Services User Guide Release 10.5.3

MSTP Support on L3 personality

The default spanning tree mode in SFS is RPVST+. On PowerSwitches in SFS mode, RPVST+ is enabled globally and automatically configured.

In L3 personality, STP is enabled on:

• SFS cluster control VLAN (VLAN 4000). The spine switches are configured to take over the STP root role.
• All user created VLANs.

In L3 personality, STP is disabled on:

• All inter leaf-spine VLANs and leaf-leaf VLANs (4001-4091).
• All server facing ports.

If you must interoperate switches that are controlled by SFS to external switches which are running RSTP or MSTP, SFS has an API to change the global fabric STP mode to MSTP. SFS creates 2 reserved MSTIs:

• MST with instance id 63: Cluster control VLAN 4000 is part of this instance. Spine switches are configured to take over as STP root for this MSTI.
• MST with instance id 62: All the SFS reserved VLANs (4001-4091) are part of this configuration. On this MSTI, spanning tree is disabled.
• All user created VLANs are part of CST (default MST instance), which interoperates with RSTP. STP is enabled for this MSTI.

You can change the mode to MSTP once the fabric is created. When you change the mode, the whole fabric goes through a reboot cycle and the new mode is set to MSTP.

When the mode is changed, MSTI is created and VLANS are assigned to the MSTI. The CST is configured with STP priority such that SFS-controlled switches have lower priority to become a root bridge.

There is no change on existing STP behavior for SFS-controlled entities because of this change. All other STP behaviors such as disabling STP on server facing ports still holds good.

You can enable MSTP or revert to RPVST using the Edit Default Fabric Settings option available in the SFS UI. Select STP Mode as MST or Rapid PVST For more information, see Edit Default Fabric Settings.