Figure 8-5 Root Port, Designated Port, Alternate Port And Backup Port - Huawei Quidway S9300 Configuration Manual

8 MSTP Configuration
Root Port
On a non-root switch, the port nearest to the root switch is the root port of the switch. A root
switch does not have a root port.
The root port forwards data to the tree root.
In Figure
of S9300B.

Figure 8-5 Root port, designated port, alternate port and backup port

S9300C
Designated Port
The designated port of a switch is the port on the upstream switch that forwards the Bridge
Protocol Data Unit (BPDU) to the local switch.
The designated port forwards data to the downstream network segment or switch.
In Figure
of S9300C.
Edge Port
An edge port is the port located at the edge of a region and is not connected to any switch.
Generally, an edge port is directly connected to the user terminals.
Alternate Port
From the aspect of sending BPDU, an alternate port is a port that is blocked after receiving the
BPDU sent by other switches. From the aspect of forwarding traffic, an alternate port is a port
that provides a backup path from the designated switch to the root switch.
An alternate port is the backup port of a root port. If the root port is blocked, the alternate port
becomes the root port.
In Figure
Backup Port
When the two ports of a switch are connected, a loop is formed, and then the switch blocks one
port. The backup port is the blocked port. In
8-6
8-5, S9300A is the root switch; CP1 is the root port of S9300C; BP1 is the root port
AP2
CP1
CP2 CP3
8-5, AP2 and AP3 are the designated ports of S9300A, and CP2 is the designated port
8-5, BP2 is the alternate port.
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S9300A
root
AP3
BP1
S9300B
BP2
Figure 8-5, CP3 is the backup port.
Quidway S9300 Terabit Routing Switch
Configuration Guide - Ethernet
root port
designated port
alternate port
backup port
Issue 03 (2009-08-20)