H3C S3600V2 SERIES, Руководство по настройке коммутации на уровне 2 в локальных сетях

Страница: 87 / 281

72
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 —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 —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 interconnected, so the device blocks one of the ports. The blocked port
acts as the backup.
•
Edge port —An edge port does not connect to any network device or network segment, but directly
connects to a user host.
•
Master port —A port on the shortest path from the local MST region to the common root bridge. The
master port is not always located on the regional root. It is a root port on the IST or CIST and still a
master port on the other MSTIs.
• Boundary port —Connects an MST region to another MST region or to an STP/RSTP-running device.
In MSTP calculation, a boundary port's role on an MSTI is consistent with its role on the CIST. But
that is not true with master ports. A master port on MSTIs is a root port on the CIST.
Port states
In MSTP, a port can be in one of the following states:
•
Forwarding —The port receives and sends BPDUs, obtains MAC addresses, and forwards user
traffic.
• Learning —The port receives and sends BPDUs, obtains MAC addresses, but does not forward user
traffic. Learning is an intermediate port state.
•
Discarding —The port receives and sends BPDUs, but does not obtain MAC addresses or forward
user traffic.
When in different MSTIs, a port can be in different states. A port state is not exclusively associated with
a port role. Table 13 lists the port states that each port role supports. (A check mark [ √ ] indicates that the
port supports this state, while a dash [—] indicates that the port does not support this state.)
Table 13 Port states that different port roles support
Port role (right)
Root port/master
port
Designated port Alternate port Backup port
Port state
(below)
Forwarding √ √ — —
Learning √ √ — —
Discarding √ √ √ √