H3C S5830V2 series, Руководство по настройке

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• The regional root of MSTI 1 is Device B.
•
The regional root of MSTI 2 is Device C.
•
The regional root of MSTI 0 (also known as the IST) is Device A.
Common root bridge
The common root bridge is the root bridge of the CIST.
In
Figure 23 , the common root bridge is a device in MST region 1.
Port roles
A port can play different roles in different MSTIs. As shown in Figure 25 , an MST region comprises Device
A, Device B, Device C, and Device D. Port A1 and port A2 of Device A connect to the common root
bridge. Port B2 and Port B3 of Device B form a loop. Port C3 and Port C4 of Device C connect to other
MST regions. Port D3 of Device D directly connects to a host.
Figure 25 Port roles
MSTP calculation involves the following port roles:
•
Root port —Forwards data for a non-root bridge to the root bridge. The root bridge does not have
any root port.
• Designated port —Forwards data to the downstream network segment or device.
•
Alternate port —Serves as the backup port for a root port or master port. When the root port or
master port is blocked, the alternate port takes over.
• Backup port —Serves as the backup port of a designated port. When the designated port is invalid,
the backup port becomes the new designated port. A loop occurs when two ports of the same
spanning tree device are connected, so the device blocks one of the ports. The blocked port acts as
the backup.
• Edge port —Does not connect to any network device or network segment, but directly connects to a
user host.