H3C S7500E Series Ethernet Switches Operation Manual

Operation Manual – MSTP
H3C S7500E Series Ethernet Switches Chapter 1 MSTP Configuration
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A boundary port is a port that connects an MST region to another MST configuration, or
to a single spanning-tree region running STP, or to a single spanning-tree region
running RSTP.
During MSTP calculation, a boundary port assumes the same role on the CIST and on
MST instances. Namely, if a boundary port is the master port on the CIST, it is also the
master port on all MST instances within this region. In
Figure 1-4, for example, if a
device in region A0 is interconnected with the first port of a device in region D0 and the
common root bridge of the entire switched network is located in region A0, the first port
of that device in region D0 is the boundary port of region D0.
 Note:
Currently, the device is not capable of recognizing boundary ports. When the device
interworks with a third party’s device that supports boundary port recognition, the third
party’s device may malfunction in recognizing a boundary port.
10) Roles of ports
In the MSTP calculation process, port roles include root port, designated port, master
port, alternate port, backup port, and so on.
z Root port: a port responsible for forwarding data to the root bridge.
z Designated port: a port responsible for forwarding data to the downstream network
segment or device.
z A master port connects an 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. In the CST, the master port is the root port of the region, which is
considered as a node. The master port is a special boundary port. It is a root port
in the IST/CIST while a master port in the other MSTIs.
z Alternate port: The standby port for the root port or master port. When the root port
or master port is blocked, the alternate port becomes the new root port or master
port.
z Backup port: The backup port of designated ports. When a designated port is
blocked, the backup port becomes a new designated port and starts forwarding
data without delay. When a loop occurs while two ports of the same MSTP device
are interconnected, the device will block either of the two ports, and the backup
port is that port to be blocked.
A port can assume different roles in different MST instances.