H3C S9500 Series Operation Manual page 17

Operation Manual – MSTP
H3C S9500 Series Routing Switches
In Figure
9) Boundary port
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 computing, a boundary port assumes the same role on the CIST and on
MSTIs. Namely, if a boundary port is master port on the CIST, it is also the master port
on all MSTIs within this region. In
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 S9500 series routing switches are not capable of recognizing boundary
ports. When an S9500 series routing switch is connected to 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
MSTP calculation involves these port roles: root port, designated port, master port,
alternate port, and backup port.
Root port: a port responsible for forwarding data to the root bridge.
Designated port: a port responsible for forwarding data to the downstream network
segment or device.
Master port: A port on the shortest path from the entire region to the common root
bridge, connecting the MST region to the common root bridge.
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.
Backup port: The backup port of designated ports. When a designated port is
blocked, the backup port becomes the 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 blocks either of the two ports, whichever is the
backup port.
A port can assume different roles in different MSTIs.
1-4, for example, the common root bridge is a device in region A0.
Figure 1-4, for example, if a device in region A0 is
1-15
Chapter 1 MSTP Configuration