3Com MSR 50 Series Configuration Manual page 456

456 C 23: MSTP C
HAPTER
n
ONFIGURATION
Figure 131 Port roles
MST region
Figure 131 helps understand these concepts. Where,
Devices A, B, C, and D constitute an MST region.
■
Port 1 and port 2 of device A connect to the common root bridge.
■
Port 5 and port 6 of device C form a loop.
■
Port 3 and port 4 of device D connect downstream to other MST regions.
■
11 Port states
In MSTP, port states fall into the following tree:
Forwarding: the port learns MAC addresses and forwards user traffic;
■
Learning: the port learns MAC addresses but does not forwards user traffic;
■
Discarding: the port neither learns MAC addresses nor forwards user traffic.
■
When in different MST instances, a port can be in different states.
A port state is not exclusively associated with a port role.
state(s) supported by each port role ("√" indicates that the port supports this
state, while "-" indicates that the port does not support this state).
Table 15 Ports states supported by different port roles
Root
port/Master
Role \State port
√
Forwarding
√
Learning
√
Discarding
Connecting to the
common root bridge
Edge port
Port 1
Master port
B
Designated
port
Port
3
Designated
port
√
√
√
Port 2
Alternate port
A
C
Port 5
D
Port
4
Table 15
Alternate port
-
-
√
Port
6
Backup port
lists the port
Backup port
-
-
√