Port State - 3Com 4210 PWR Configuration Manual

Figure 50 Port roles

Port state

In MSTP, a port can be in one of the following three states:
■
■
■
Port roles and port states are not mutually dependent. Table 100 lists possible
combinations of port states and port roles.
Table 100 Combinations of port states and port roles
Principle of MSTP MSTP divides a Layer 2 network into multiple MST regions. The CSTs are generated
between these MST regions, and multiple spanning trees (also called MSTIs) can
be generated in each MST region. As well as RSTP, MSTP uses configuration BPDUs
for spanning tree calculation. The only difference is that the configuration BPDUs
for MSTP carry the MSTP configuration information on the switches.
Calculate the CIST
Through comparing configuration BPDUs, the switch of the highest priority in the
network is selected as the root of the CIST. In each MST region, an IST is calculated
by MSTP. At the same time, MSTP regards each MST region as a switch to calculate
the CSTs of the network. The CSTs, together with the ISTs, form the CIST of the
network.
Connected to the Connected to the Connected to the Connected to the
common root common root common root common root
Edge port Edge port Edge port Edge port
MST region MST region MST region MST region MST region Port 1 Port 1 Port 1 Port 1
port port port port
Master Master Master Master
B B B B
Designated Designated Designated Designated
Port 3 Port 3 Port 3 Port 3
port port port port
Forwarding state. Ports in this state can forward user packets and receive/send
BPDU packets.
Learning state. Ports in this state can receive/send BPDU packets.
Discarding state. Ports in this state can only receive BPDU packets.
Root/
Port role/ port/Master
Port state port
Forwarding ‚X
Learning ‚X
Discarding ‚X
Port 2 Port 2 Port 2 Port 2
Alternate port Alternate port Alternate port Alternate port
A A A A
C C C C C
Port 6 Port 6 Port 6 Port 6
Port 5 Port 5 Port 5 Port 5
D D D D
Backup Backup Backup Backup
Port 4 Port 4 Port 4 Port 4
Designated Region edge
port port
‚X ‚X
‚X ‚X
‚X ‚X
MSTP Overview
port port port port
Alternate
port Backup port
- -
- -
‚X ‚X
151