Rstp Port States; Rapid-Pvst; Understanding How Ieee 802.1S Mst Works - Cisco 7609 Configuration Manual

Understanding How 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 15-4 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 IEEE 802.1s MST Works
In Cisco IOS release 12.1(11)EX and later releases, RSTP is implemented as part of Multiple Spanning
Note
Tree Protocol (MSTP). In Cisco IOS release 12.1(13)E and later releases, RSTP is also available as a
standalone protocol in Rapid-Per-VLAN-Spanning Tree (Rapid-PVST) mode. In this mode, the switch
runs an RSTP instance on each VLAN, which follows the usual PVST+ approach.
Cisco 7600 Series Router Cisco IOS Software Configuration Guide—12.1E
15-14
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 15-4
STP Port State
Blocking
Listening
Learning
Forwarding
Disabled
provides a comparison between STP port states and RSTP port
RSTP Port State
1 2
Discarding
Discarding
Learning
Forwarding
Discarding
Chapter 15 Configuring STP and IEEE 802.1s MST
Port Included in Active Topology
No
No
Yes
Yes
No
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