Implementation Of Mstp - Huawei Quidway S3100 Series Operation Manual

Operation Manual – MSTP
Quidway S3100 Series Ethernet Switches
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.
Table 1-1 lists possible combinations of port states and port roles.
Table 1-1 Combinations of port states and port roles
Port
state
Forwarding
Learning
Discarding

1.1.3 Implementation of MSTP

MSTP divides a network into multiple MST regions at Layer 2. The CST is generated
between these MST regions, and multiple spanning trees (or, MSTIs) can be generated
in each MST region. As well as RSTP, MSTP uses configuration BPDUs to generate
spanning trees. The only difference is that the configuration BPDUs for MSTP carry the
MSTP configuration information on the switches.
I. Generating the CIST
Through configuration BPDU comparing, the switch that is of the highest priority in the
network is chosen as the root of the CIST. In each MST region, an IST is figured out by
MSTP. At the same time, MSTP regards each MST region as a switch to figure out the
CST of the network. The CST, together with the ISTs, forms the CIST of the network.
II. Generating an MSTI
In an MST region, different MSTIs are generated for different VLANs depending on the
VLAN-to-spanning-tree mappings. Each spanning tree is figured out independently, in
the same way as STP/RSTP.
III. Implementation of STP algorithm
In the beginning, each switch regards itself as the root, and generates a configuration
BPDU for each port on it as a root, with the root path cost being 0, the ID of the
designated bridge being that of the switch, and the designated port being itself.
1) Each switch sends out its configuration BPDUs and operates in the following way
when receiving a configuration BPDU on one of its ports from another switch:
Port
Root/
role
port/Mast
er port
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Huawei Technologies Proprietary
Designat Region
ed port edge port
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1-5
Chapter 1 MSTP Configuration
Alternate Backup
port port
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