How Mstp Works; Mstp Implementation On Devices - HP 1920 Series User Manual

port state is available for the corresponding port role, and a dash [—] indicates that the port state is not
available for the corresponding port role.)
Table 57 Ports states supported by different port roles

How MSTP works

MSTP divides an entire Layer 2 network into multiple MST regions, which are connected by a calculated
CST. Inside an MST region, multiple spanning trees, called MSTIs, are calculated. Among these MSTIs,
MSTI 0 is the CIST.
Similar to RSTP, MSTP uses configuration BPDUs to calculate spanning trees. An important difference is
that an MSTP BPDU carries the MSTP configuration of the bridge from which the BPDU is sent.
CIST calculation
The calculation of a CIST tree is also the process of configuration BPDU comparison. During this process,
the device with the highest priority is elected as the root bridge of the CIST. MSTP generates an IST within
each MST region through calculation. At the same time, MSTP regards each MST region as a single
device and generates a CST among these MST regions through calculation. The CST and ISTs constitute
the CIST of the entire network.
MSTI calculation
Within an MST region, MSTP generates different MSTIs for different VLANs based on the
VLAN-to-instance mappings. For each spanning tree, MSTP performs a separate calculation process,
which is similar to spanning tree calculation in STP/RSTP. For more information, see
of the STP
In MSTP, a VLAN packet is forwarded along the following paths:
•
•

MSTP implementation on devices

MSTP is compatible with STP and RSTP. STP and RSTP protocol packets can be recognized by devices
running MSTP and used for spanning tree calculation.
In addition to basic MSTP functions, the device provides the following functions for ease of management:
•
•
•
•
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Port role
Port state
Root port/master
port
Forwarding √
Learning √
Discarding √
algorithm"
Within an MST region, the packet is forwarded along the corresponding MSTI.
Between two MST regions, the packet is forwarded along the CST.
Root bridge hold
Root bridge backup
Root guard
BPDU guard
manuals search engine
Designated Boundary
port port
√ √
√ √
√ √
189
Alternate port Backup port
— —
— —
√ √
"Calculation process