Rstp Port States; Understanding How Prestandard Ieee 802.1S Mst Works - Cisco 7604 Configuration Manual

Understanding How Prestandard IEEE 802.1s MST Works

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Port roles are assigned as follows:
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RSTP Port States

The port state controls the forwarding and learning processes and provides the values of discarding,
learning, and forwarding.
states.
Table 20-4 Comparison Between STP and RSTP Port States
Operational Status
Enabled
Enabled
Enabled
Enabled
Disabled
1. IEEE 802.1D port state designation.
2. IEEE 802.1w port state designation. Discarding is the same as blocking in RSTP and MST.
In a stable topology, RSTP ensures that every root port and designated port transition to forwarding, and
ensures that all alternate ports and backup ports are always in the discarding state.
Rapid-PVST
Rapid-PVST uses the existing configuration for PVST+; however, Rapid-PVST uses RSTP to provide
faster convergence. Independent VLANs run their own RSTP instance.
Dynamic entries are flushed immediately on a per-port basis upon receiving a topology change.
UplinkFast and BackboneFast configurations are ignored in Rapid-PVST mode; both features are
included in RSTP.
Understanding How Prestandard IEEE 802.1s MST Works
These sections describe Multiple Spanning Tree (MST):
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Cisco 7600 Series Router Cisco IOS Software Configuration Guide, Release 12.2SX
20-14
Backup—A backup for the path provided by a designated port toward the leaves of the spanning tree.
Backup ports can exist only where two ports are connected together in a loopback by a point-to-point
link or bridge with two or more connections to a shared LAN segment.
Disabled—A port that has no role within the operation of spanning tree.
A root port or designated port role includes the port in the active topology.
An alternate port or backup port role excludes the port from the active topology.
Table 20-4
STP Port State
Blocking
Listening
Learning
Forwarding
Disabled
IEEE 802.1s MST Overview, page 20-15
MST-to-PVST Interoperability, page 20-16
Common Spanning Tree, page 20-18
Chapter 20
provides a comparison between STP port states and RSTP port
RSTP Port State
1 2
Discarding
Discarding
Learning
Forwarding
Discarding
Configuring STP and Prestandard IEEE 802.1s MST
Port Included in Active Topology
No
No
Yes
Yes
No
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