Falcon
M-Class
| User Guide
232
If another RSTP device receives this information and determines that this is the superior root
information, it starts a synchronizing operation to ensure all of its ports are in sync with the new
information. This device may send an “agreement” to the first RSTP device confirming its superior
spanning tree information.
The first RSTP device, upon receiving this agreement, knows now that it can rapidly change that
port to the forwarding state.
Similar proposal agreement handshake messages propagate within the network, restoring the
connectivity very quickly after a topology change, bypassing the traditional listening/learning state
transition process.
Therefore a cascading effect is created away from the RSTP root where each designated port
proposes to its neighbors to determine if a rapid transition is possible. In this way RSTP achieves
faster convergence times than STP.
RSTP device port roles:
Root
–
A forwarding port that is the best port from no root-bridge to Root bridge
Designated
–
A forwarding port for every LAN segment
Alternate
–
An alternate port to the root bridge
Disabled
–
A network administrator can manually disable a port
Backup
–
provides an alternate designated port
Understanding MSTP
RSTP does not solve the problem inherent in STP: all VLANs within a LAN must share the
same spanning tree topology. An STP or RSTP network has only one spanning tree instance for the
entire network and includes all VLANs in the network.
µFalcon switches utilize the Multiple Spanning Tree protocol (MSTP, 802.1s) to ensure that only
one active path exists between any two nodes in a spanning tree instance.
An instance includes a unique set of VLANs, belongs to a specific spanning tree region and creates a
separate per instance forwarding topology.
A region may comprise multiple spanning tree instances (each with a different set of VLANs)
Each spanning tree instance is independent of other instances. Each region can support up to 16
spanning tree instances.
MSTP region: a group of interconnected switches that share the same attributes is defined as an
MST region. An MST region includes multiple spanning tree instances (MSTI) which provide
different paths for different VLAN. Each MSTI can have its own independent topology.
Note that MSTP recognizes an STP or RSTP LAN as a distinct spanning tree region.
A region can include two types of STP instances:
•
Internal Spanning Tree Instance (IST instance). This is the default spanning tree instance in
any MST region.IST provides the root switch for the region and by default comprises all
Summary of Contents for Falcon Gen-3 M-Class
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Page 107: ...Falcon M Class User Guide 107 Figure 4 57 DSCP Translation...
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