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Catalyst 4500 Series, Catalyst 2948G, Catalyst 2948G-GE-TX, and Catalyst 2980G Switches Software Configuration Guide—Release 8.2GLX
78-15908-01
Chapter 7 Configuring Spanning Tree
Understanding How MST Works
RSTP Port States
The port state controls the forwarding and learning processes and provides the values of discarding,
learning, and forwarding. See
Table 7-3
for a comparison between STP port states and RSTP port states.
In a stable topology, RSTP ensures that every root port and designated port transition to forwarding while
all alternate ports and backup ports are always in the discarding state.
MST-to-SST Interoperability
A virtual bridged LAN may contain interconnected regions of SST and MST bridges. See
Figure 7-8
.
Figure 7-8
Network with Interconnected SST and MST Regions
Table 7-3
Comparison Between STP and RSTP Port States
Operational Status
STP Port State
RSTP Port State
Port Included in Active Topology?
Enabled
Blocking
1
1.
IEEE 802.1D port state designation.
Discarding
2
2.
IEEE 802.1w port state designation. In this publication, discarding is the same as blocking in MST.
No
Enabled
Listening
Discarding
No
Enabled
Learning
Learning
Yes
Enabled
Forwarding
Forwarding
Yes
Disabled
Disabled
Discarding
No
MST
Region
MST
Region
SST
Region
SST
Region
F
F
F
F
F
F
R
F
F
F
F
F
F
F
B
B
B
B
B
r
r
r
r
r
r
r
b
b
F/f = Forwarding
B/b = Blocking
R = Root Bridge
r = Root port
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