HPE FlexNetwork MSR Series User Manual

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A port can have different port states in different MSTIs. A port state is not exclusively associated with
a port role. Table 141 list
s
the port states supported by each port role. ("√" indicates that the port state
is available for the corresponding port role and "—" indicates that the port state is not available for
the corresponding port role.)
Table 141 Ports states supported by different port roles
Port state
Port role
Root
port/master port
Designate
d port
Boundary
port
Alternate
port
Backup
port
Forwarding √ √ √ — —
Learning √ √ √ — —
Discarding √ √ √ √ √
How MSTP works
MSTP divides an entire Layer 2 network into multiple MST regions, which are interconnected by a
calculated CST. Inside an MST region, multiple spanning trees are calculated, each being an MSTI
(Among these MSTIs, MSTI 0 is called the CIST). Similar to RSTP, MSTP uses configuration BPDUs
to calculate spanning trees. The only difference between the two protocols is that an MSTP BPDU
carries the MSTP configuration on the device from which this 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, and, 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. MSTP performs a separate calculation process, which is similar to
spanning tree calculation in STP/RSTP, for each spanning tree. For more information, see "How STP
wo
r
ks."
In MSTP, a VLAN packet is forwarded along the following paths:
• Within an MST region, the packet is forwarded along the corresponding MSTI.
• Between two MST regions, the packet is forwarded along the CST.
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:
• Root bridge hold
• Root bridge backup
• Root guard
• BPDU guard
• Loop guard
• TC-BPDU guard

HPE FlexNetwork MSR Series Specifications

General

Brand	HPE
Model	FlexNetwork MSR Series
Category	Network Router
Language	English