F3726, F3211, F3174, R5135, R3816-HP Firewalls and UTM Devices Network Management Configuration Guide-6PW100

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• Same VLAN-to-instance mapping configuration.
• Same MSTP revision level.
• Physically linked together.
Multiple MST regions can exist in a switched network. You can assign multiple devices to the same MST
region. In
2206HFigure 42, the switched network comprises MST region 1 through MST region 4, and all
devices in each MST region have the same MST region configuration.
1115BMSTI
MSTP can generate multiple independent spanning trees in an MST region, and each spanning tree is
mapped to specific VLANs. Each spanning tree is called a "multiple spanning tree instance (MSTI)."
In
2207HFigure 43, MST region 3 comprises MSTI 1, MSTI 2, and MSTI 0.
1116BVLAN-to-instance mapping table
As an attribute of an MST region, the VLAN-to-instance mapping table describes mapping relationships
between VLANs and MSTIs.
In
2208HFigure 43, the VLAN-to-instance mapping table of MST region 3 is: VLAN 1 to MSTI 1, VLAN 2 and
VLAN 3 to MSTI 2, and other VLANs to MSTI 0. MSTP achieves load balancing by means of the
VLAN-to-instance mapping table.
1117BCST
The common spanning tree (CST) is a single spanning tree that connects all MST regions in a switched
network. If you regard each MST region as a device, the CST is a spanning tree calculated by these
devices through STP or RSTP.
The blue lines in
2209HFigure 42 represent the CST.
1118BIST
An internal spanning tree (IST) is a spanning tree that runs in an MST region. It is also called MSTI 0, a
special MSTI to which all VLANs are mapped by default.
In
2210HFigure 42, MSTI 0 is the IST in MST region 3.
1119BCIST
The common and internal spanning tree (CIST) is a single spanning tree that connects all devices in a
switched network. It consists of the ISTs in all MST regions and the CST.
In
2211HFigure 42, the ISTs (MSTI 0) in all MST regions plus the inter-region CST constitute the CIST of the entire
network.
1120BRegional root
The root bridge of the IST or an MSTI within an MST region is the regional root of the IST or MSTI. Based
on the topology, different spanning trees in an MST region might have different regional roots.
In MST region 3 in
2212HFigure 43, the regional root of MSTI 1 is Device B, the regional root of MSTI 2 is
Device C, and the regional root of MSTI 0 (also known as the IST) is Device A.
1121BCommon root bridge
The common root bridge is the root bridge of the CIST.
In
2213HFigure 42, the common root bridge is a device in MST region 1.