3Com Switch 4800G 24-Port Configuration Manual page 210

210 C 23: MSTP C
HAPTER
n
ONFIGURATION
Figure 57 Port roles
Edge ports
MST region
Master port
Designated port
Figure 57 helps understand these concepts. Where,
Devices A, B, C, and D constitute an MST region.
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Port 1 and port 2 of device A connect to the common root bridge.
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Port 5 and port 6 of device C form a loop.
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Port 3 and port 4 of device D connect downstream to other MST regions.
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11 Port states
In MSTP, port states fall into the following tree:
Forwarding: the port learns MAC addresses and forwards user traffic;
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Learning: the port learns MAC addresses but does not forward user traffic;
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Discarding: the port neither learns MAC addresses nor forwards user traffic.
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When in different MST instances, a port can be in different states.
The role a boundary port plays in an MSTI is consistent with the role it plays in
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the CIST. The master port, which is a root port in the CIST while a master port
in the other MSTIs, is an exception.
For example, in Figure 57, port 1 on switch A is a boundary port. It is a root
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port in the CIST while a master port in all the other MSTIs in the region.
A port state is not exclusively associated with a port role. Table 42 lists the port
state(s) supported by each port role ("‚àö" indicates that the port supports this
state, while "-" indicates that the port does not support this state).
Connecting to the
common root bridge
Port 2
Port 1
Alternate port
A
B
C
D
Port 3 Port 4
Port 6
Port 5
Backup port