Netgear GS728TPP User Manual download pdf (Page 267)

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GS752TP, GS728TP, and GS728TPP Gigabit Smart Switches

receive and transmit MSTP BPDUs. The MST configuration identifier has 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 table (a VLAN ID to MSTID mapping)

As there are multiple instances of spanning tree, there is an MSTP state maintained on a

per-port, per-instance basis (or on a per port, per VLAN basis, as any VLAN can be in only

one MSTI or CIST). For example, port A can be forwarding for example 1 while discarding for

example 2. The port states have changed since IEEE 802.1D specification.

To support multiple spanning trees, an MSTP bridge has to be configured with an

unambiguous assignment of VLAN IDs (VIDs) to spanning trees. This is achieved by:

1. Ensuring that the allocation of VIDs to FIDs is unambiguous.

2. Ensuring that each FID 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, every VLAN is assigned to only one MSTI. The CIST is also an instance

of spanning tree with an MSTID of 0.

An instance might occur that has no VIDs allocated to it, 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.

Sample MSTP Configuration

This example shows how to create an MSTP instance from the switch. The sample network

has three different switches that serve different locations in the network.

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Netgear GS728TPP User Manual Page 267