Huawei Quidway S3000-EI Series Operation Manual page 182

Operation Manual - STP
Quidway S3000-EI Series Ethernet Switches
VIII. Common Root Bridge
The Common Root Bridge refers to the root bridge of CIST. There is only one common
root bridge in the specified network.
IX. Edge port
The edge port refers to the port located at the MST region edge, connecting different
MST regions, MST region and STP region, or MST region and RSTP region. For MSTP
calculation, the edge port shall take the same role on MSTI and CIST instance. For
example, the edge port as a master port on CIST instance should serve as a master
port on every MSTI in the region.
X. Port role
In the process of MSTP calculation, a port can serve as a designated port, root port,
master port, Alternate port, or BACKUP.
The root port is the one through which the data are forwarded to the root.
The designated port is the one through which the data are forwarded to the
downstream network segment or switch.
Master port is the port connecting the entire region to the Common Root Bridge
and located on the shortest path between them.
Alternate port is the backup of the master port. When the master port is blocked,
the alternate port will take its place.
If two ports of a switch are connected, there must be a loop. In this case, the switch
will block one of them. The blocked one is called BACKUP port.
A port can play different roles in different spanning tree instances.
The following figure illustrates the above mentioned concepts for your better
understanding.
EdgePort
MST region
Master
Designated
port
Figure 1-2 Port roles
Connected to the
common root
Port 2
Port 1
Alternate port
port
A
B
Port 5
D
Port 3
Port 4
Huawei Technologies Proprietary
Chapter 1 MSTP Region-configuration
C
Port 6
Backup port
1-3