User Manual

24-Port and 48-Port Gigabit Ethernet PoE+ Smart Switches with 4 SFP Ports
Configuration Examples User Manual529
An MST region comprises of one or more MSTP bridges with the same MST configuration
identifier, using the same MSTIs, and without any bridges attached that cannot receive and
transmit MSTP BPDUs. The MST configuration identifier includes the following components:
1. Configuration identifier format selector
2. Configuration name
3. Configuration revision level
4. Configuration digest: 16-byte signature of type HMAC-MD5 created from the MST
Configuration T
able (a VLAN ID to MSTID mapping)
Because multiple instances of spanning tree exist, an MSTP state is maintained on a
per-port, per-instance basis (or on a per-port, per-VLAN basis, as any VLAN can be in one
and only one MSTI or CIST). For example, port
A can be forwarding for instance 1 while
discarding for instance 2. The port states changed since IEEE 802.1D specification.
To support multiple spanning trees, configure an MSTP bridge with an unambiguous
assignment of VLAN IDs (VIDs) to spanning trees. For such a configuration, ensure the
following:
1. The allocation of VIDs to FIDs is unambiguous.
2. Each FID that is supported by the bridge is allocated to exactly one spanning tree instance.
The combination of VID to FID and then FID to MSTI allocation defines a mapping of VIDs to
spanning tree instances, represented by the MST Configuration
Table.
With this allocation we ensure that every VLAN is assigned to one and only one MSTI. The
CIST is also an instance of spanning tree with an MSTID of 0.
VIDs might be not be allocated to an instance, but every VLAN must be allocated to one of
the other instances of spanning tree.
The portion of the active topology of the network that connects any two bridges in the same
MST region traverses only MST bridges and LANs in that region, and never bridges of any
kind outside the region. In other words, connectivity within the region is independent of
external connectivity
.
MSTP example configuration
This example shows how to create an MSTP instance from the switch. The example network
includes three different switches that serve different locations in the network. In this example,
ports 1/0/1–1/0/5 are connected to host stations, so those links are not subject to network
loops. Ports 1/0/6–1/0/8 are connected across switches 1, 2, and 3.