In an MSTP, ports can be in the following four states:
Forwarding: In this status the port can receive/forward data, receive/send BPDU packets
as well as learn MAC address.
Learning: In this status the port can receive/send BPDU packets and learn MAC address.
Blocking: In this status the port can only receive BPDU packets.
Disconnected: In this status the port is not participating in the STP.
Port Roles
In an MSTP, the following roles exist:
Root Port: The port selected on non-root bridges to provide the lowest root path cost.
There is only one root port in each non-root bridge.
Designated Port: The port selected for each LAN segment to provide the lowest root path
cost from that LAN segment to the root bridge
Master Port: Indicates the port that connects a MST region to the common root. The path
from the master port to the common root is the shortest path between this MST region
and the common root.
Alternate Port: If a port is not selected as the designated port for it receives better BPDUs
from another switch, it will become an alternate port.
In RSTP/MSTP, the alternate port is the backup for the root port. It is blocked when the root
port works normally. Once the root port fails, the alternate port will become the new root
port.
In STP, the alternate port is always blocked.
Backup Port:
If a port is not selected as the designated port for it receives better BPDUs
from the switch it belongs to, it will become a backup port.
In RSTP/MSTP, the designated port is the backup for the designated port. It is blocked
when the designated port works normally. Once the root port fails, the backup port will
become the new designated port.
In STP, the backup port is always blocked.
Disabled: Indicates the port that is not participating in the STP.
The following diagram shows the different port roles.
Figure 8-3 Port roles
The Spanning Tree module is mainly for spanning tree configuration of the switch, including
four submenus:
STP Config
,
Port Config
,
MSTP Instance
and
STP Security
.
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