19
• Within an MST region, the frame is forwarded along the corresponding MSTI.
• Between two MST regions, the frame is forwarded along the CST.
MSTP implementation on devices
MSTP is compatible with STP and RSTP. Devices that are running MSTP and that are used for
spanning tree calculation can identify STP and RSTP protocol frames.
In addition to basic MSTP features, the following features are provided for ease of management:
• Root bridge hold.
• Root bridge backup.
• Root guard.
• BPDU guard.
• Loop guard.
• TC-BPDU guard.
• Port role restriction.
• TC-BPDU transmission restriction.
Rapid transition mechanism
In STP, a port must wait twice the forward delay (30 seconds by default) before it transits from the
blocking state to the forwarding state. The forward delay is related to the hello time and network
diameter. If the forward delay is too short, loops might occur. This affects the stability of the network.
RSTP, PVST, and MSTP all use the rapid transition mechanism to speed up port state transition for
edge ports, root ports, and designated ports. The rapid transition mechanism for designated ports is
also known as the proposal/agreement (P/A)_transition.
Edge port rapid transition
As shown in Figure 12, Port C3 is an edge port connected to a host. When a network topology
change occurs, the port can immediately transit from the blocking state to the forwarding state
because no loop will be caused.
Because a device cannot determine whether a port is directly connected to a terminal, you must
manually configure the port as an edge port.
Figure 12 Edge port rapid transition
To Next Page
Loading...
Need help?
General