Spanning tree operation with switch meshing
Switch meshing cannot run concurrently with RPVST+.
Using MSTP with several switches and no switch meshing configured can result in unnecessarily blocking links and reducing available bandwidth. For example:
Using STP without and with switch meshing
Connecting a switch mesh domain to non-meshed devices
If you are going to use spanning tree in a switch mesh, all switches in the mesh should be configured with the same type of spanning tree: 802.1d/STP, 802.1w/RSTP, or 802.1s/MSTP. spanning tree interprets a meshed domain as a single link. However, on edge switches in the domain, MSTP will manage non-meshed redundant links from other devices. For example:
When using MSTP and interconnecting switches
covered in this guide in a mesh with switches that are not in the
mesh, all the non-mesh switch ports should have the edge-port parameter disabled.
Interconnecting switch mesh domains with redundant links
MSTP should be configured on non-mesh devices that use redundant links to interconnect with other devices or with multiple switch mesh domains. For example:
In the above case of multiple switch meshes linked with redundant trunks, there is the possibility that spanning tree will temporarily block a mesh link. This is because it is possible for spanning tree to interpret the cost on an external trunked link to be less than the cost on a meshed link. However, if this condition occurs, the meshed switch that has a blocked link will automatically increase the cost on the external (non-meshed) link to the point where spanning tree will block the external link and unblock the meshed link. This process typically resolves itself in approximately 30 seconds.