1-13
Figure 1-5 Port roles
Connecting to the
common root bridge
Port 1
Port 2
Master port Alternate port
Designated port
Port 3 Port 4
Port 5
A
B
C
D
Port 6
Backup port
MST region
In
Figure 1-5, devices A, B, C, and D constitute an MST region. Port 1 and port 2 of device A are
connected to the common root bridge, port 5 and port 6 of device C form a loop, port 3 and port 4 of
Device D are connected downstream to the other MST regions.
Port states
In MSTP, port states fall into the following three:
z Forwarding: the port learns MAC addresses and forwards user traffic;
z Learning: the port learns MAC addresses but does not forward user traffic;
z Discarding: the port does not learn MAC addresses or forwards user traffic.
A port can have different port states in different MSTIs.
A port state is not exclusively associated with a port role.
Table 1-6 lists the port state(s) supported by
each port role. (“√” indicates that the port state is available for the corresponding port role; “—” indicates
that the port state is not available for the corresponding port role.)
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