Huawei Quidway S3100 Series Operation Manual page 160

Operation Manual – MSTP
Quidway S3100 Series Ethernet Switches
A master port connects a MST region to the common root. The path from the
master port to the common root is the shortest path between the MST region and
the common root.
A region edge port is located on the edge of an MST region and is used to connect
the MST region to another MST region, an STP-enabled region, or an
RSTP-enabled region.
An alternate port can be a backup port of a master or root port. When it operates
as a backup port of a master port, it becomes the master port if the existing master
port is blocked.
A loop occurs when two ports of a switch are connected to each other. In this case,
the switch blocks one of the two ports. The blocked port is a backup port.
In Figure 1-2, switch A, B, C, and D form an MST region. Port 1 and port 2 on switch A
connect upstream to the common root. Port 5 and port 6 on switch C form a loop. Port 3
and port 4 on switch D connect downstream to other MST regions. This figure shows
the roles these ports play.
Note:
A port can play different roles in different MSTIs.
The role a region edge port plays is consistent with the role it plays in the CIST. For
example, port 1 on switch A in Figure 1-2 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.
EdgePort
MST region
Master
Designated
port
Figure 1-2 Port roles
X. Port states
Ports can be in the following three states:
Connected to the
common root
Port 2
Port 1
Alternate port
port
A
B
Port 5
D
Port 3
Port 4
Huawei Technologies Proprietary
C
Port 6
Backup port
1-4
Chapter 1 MSTP Configuration