H3C Technologies H3C WX3000 Series Unified Switches - Manual (Page 181)

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port 4 on device D connect downstream to other MST regions. This figure shows the roles these ports
play.
z
A port can play different roles in different MSTIs.
z
The role a region edge port plays is consistent with the role it plays in the CIST. For example, port
1 on device A in
Figure 22-5 is a region edge port, and it is a master port in the CIST. So it is a
master port in all MSTIs in the region.
Figure 22-5 Port roles
Edge ports
Connected to the
common port
Port 1
Port 2
Port 3 Port 4
Port 5
Port 6
MST
region
Designated
port
Master
port
Backup port
Alternate port
A
B
D
C
Port state
In MSTP, a port can be in one of the following three states:
z
Forwarding state. Ports in this state can forward user packets and receive/send BPDU packets.
z
Learning state. Ports in this state can receive/send BPDU packets.
z
Discarding state. Ports in this state can only receive BPDU packets.
Port roles and port states are not mutually dependent. Table 22-6 lists possible combinations of port
states and port roles.
Table 22-6 Combinations of port states and port roles
Port role
(right)
Port state
(below)
Root/
port/Master
port
Designated
port
Region edge
port
Alternate port Backup port
Forwarding √ √ √ — —