How Mstp Works; Implementation Of Mstp On Devices; Protocols And Standards - HP 3100 Series Configuration Manual

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 are calculated. Each spanning tree is
an MSTI. Among these MSTIs, MSTI 0 is the IST. Like STP, 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 similar to spanning tree calculation in STP. For more information, see
of the STP algorithm."
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.

Implementation of MSTP on devices

MSTP is compatible with STP and RSTP. Devices that are running MSTP and that are used for
spanning tree calculation can identify STP and RSTP protocol packets.
In addition to basic MSTP functions, the following functions are provided for ease of management:
•
Root bridge hold
•
Root bridge backup
•
Root guard
•
BPDU guard
•
Loop guard
•
TC-BPDU guard
•
BPDU drop

Protocols and standards

The spanning tree protocols are documented in the following standards:
•
IEEE 802.1d, Media Access Control (MAC) Bridges
•
IEEE 802.1w, Part 3: Media Access Control (MAC) Bridges—Amendment 2: Rapid
Reconfiguration
•
IEEE 802.1s, Virtual Bridged Local Area Networks—Amendment 3: Multiple Spanning Trees
60
"Calculation process