210 CHAPTER 23: MSTP CONFIGURATION
Figure 57 Port roles
Figure 57 helps understand these concepts. Where,
■ Devices A, B, C, and D constitute an MST region.
■ Port 1 and port 2 of device A connect to the common root bridge.
■ Port 5 and port 6 of device C form a loop.
■ Port 3 and port 4 of device D connect downstream to other MST regions.
11 Port states
In MSTP, port states fall into the following tree:
■ Forwarding: the port learns MAC addresses and forwards user traffic;
■ Learning: the port learns MAC addresses but does not forward user traffic;
■ Discarding: the port neither learns MAC addresses nor forwards user traffic.
n
When in different MST instances, a port can be in different states.
■ The role a boundary port plays in an MSTI is consistent with the role it plays in
the CIST. The master port, which is a root port in the CIST while a master port
in the other MSTIs, is an exception.
■ For example, in Figure 57, port 1 on switch A is a boundary port. It is a root
port in the CIST while a master port in all the other MSTIs in the region.
A port state is not exclusively associated with a port role. Table 42 lists the port
state(s) supported by each port role (“‚àö” indicates that the port supports this
state, while “-” indicates that the port does not support this state).
Connecting to the
common root bridge
Edge ports
Port 1
Port 2
Master port Alternate port
Designated port
Port 3 Port 4
Port 5
A
B
C
D
Port 6
Backup port
MST region
To Next Page
Loading...
