Qtech QSW-2900-24T-AC [150/209] Mst region

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Figure 4 Basic concepts in MSTP

1) MST region

An MST region is composed of multiple devices in a switched network and network segments among them.

These devices have the following characteristics:

· All are MSTP-enabled,

· They have the same region name,

· They have the same VLAN-to-instance mapping configuration,

· They have the same MSTP revision level configuration, and

· They are physically linked with one another.

In region A0 in Figure 4, for example, all the device have the same MST region configuration: the same

region name, the same VLAN-to-instance mapping (VLAN1 is mapped to MST instance 1, VLAN2 to MST instance

2, and the rest to the command and internal spanning tree (CIST). CIST refers to MST instance 0), and the same

MSTP revision level (not shown in the figure).

Multiple MST regions can exist in a switched network. You can use an MSTP command to group multiple

devices to the same MST region.

2) VLAN-to-instance mapping table

As an attribute of an MST region, the VLAN-to-instance mapping table describes the mapping relationships

between VLANs and MST instances. In Figure 4, for example, the VLAN-to-instance mapping table of region A0

describes that the same region name, the same VLAN-to-instance mapping (VLAN1 is mapped to MST instance 1,

VLAN2 to MST instance 2, and the rest to CIST.

3) IST

Internal spanning tree (IST) is a spanning tree that runs in an MST region, with the instance number of 0. ISTs

in all MST regions and the common spanning tree (CST) jointly constitute the common and internal spanning tree

(CIST) of the entire network. An IST is a section of the CIST in an MST region. In Figure 4, for example, the CIST

has a section is each MST region, and this section is the IST in each MST region.