H3C Technologies H3C S5560 Series Switches - Manual (Page 108)

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• MSTP generates an IST within each MST region through calculation.
• 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 " Calculation process 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.
MSTP implementation 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
• Port role restriction
• TC-BPDU transmission restriction
Protocols and standards
MSTP is documented in the following protocols and 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
• IEEE 802.1Q-REV/D1.3, Media Access Control (MAC) Bridges and Virtual Bridged Local Area
Networks —Clause 13: Spanning tree Protocols
Spanning tree configuration task lists
Before configuring a spanning tree, complete the following tasks:
• Determine the spanning tree protocol to be used (STP, RSTP, PVST, or MSTP).
• Plan the device roles (the root bridge or leaf node).