Mst-To-Sst Interoperability - Cisco 4500M Software Manual

Overview of MST
RSTP Port States
The port state controls the forwarding and learning processes and provides the values of discarding,
learning, and forwarding.
Table 16-1 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 MST.
In a stable topology, RSTP ensures that every root port and designated port transitions to the forwarding
state 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.
this relationship.
Figure 16-1 Network with Interconnected SST and MST Regions
SST
Region
F/f = Forwarding
B/b = Blocking
R = Root Bridge
r
Software Configuration Guide—Release 12.2(25)EW
16-4
Table 16-1
STP Port State
Blocking
Listening
Learning
Forwarding
Disabled
MST
Region
B
F
F
r
b r
F
r
F
F
= Root port
Chapter 16
shows the STP port states and RSTP port states.
RSTP Port State
1 2
Discarding
Discarding
Learning
Forwarding
Discarding
B
r
B
F B
F
F
F
R
MST
Region
Understanding and Configuring Multiple Spanning Trees
Port Included in Active Topology
No
No
Yes
Yes
No
F
F
F
r
r
r
b SST
F
Region
B
Figure 16-1 shows
OL-6696-01