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Switch Meshing
Operating Notes for Switch Meshing
Note on the Edge-
Port Mode in MSTP
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
(as indicated in the figure above) should have the edge-port parameter dis-
abled.
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:
Mesh Domain
STP
Block
STP
Block
Mesh Domain
Non-Mesh Switch
Non-Mesh Switch
Figure 5-17. Interconnecting Switch Mesh Domains with Redundant Links
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 automat-
ically 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.
Caution Spanning tree interprets a switch mesh as a single link. Because the switch
automatically gives faster links a higher priority, the default spanning-tree
parameter settings are usually adequate for spanning tree operation. Also,
because incorrect spanning tree settings can adversely affect network perfor-
mance, you should not make changes unless you have a strong understanding
of how spanning tree operates.
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