D-Link DSA-3200 Technical Information download pdf (Page 105)

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DGS-3200 Series Layer 2 Managed Gigabit Ethernet Switch Web UI Reference Guide

NOTE: Target mirror ports cannot be members of a trunking group. Attempting to do so will

produce an error message and the configuration will not be set.

Spanning Tree

This Switch supports three versions of the Spanning Tree Protocol: 802.1D-1998 STP, 802.1D-2004 Rapid STP, and 802.1Q-2005

MSTP. 802.1D-1998 STP will be familiar to most networking professionals. However, since 802.1D-2004 RSTP and 802.1Q-

2005 MSTP have been recently introduced to D-Link managed Ethernet switches, a brief introduction to the technology is

provided below followed by a description of how to set up 802.1D-1998 STP, 802.1D-2004 RSTP, and 802.1Q-2005 MSTP.

802.1Q-2005 MSTP

Multiple Spanning Tree Protocol, or MSTP, is a standard defined by the IEEE community that allows multiple VLANs to be

mapped to a single spanning tree instance, which will provide multiple pathways across the network. Therefore, these MSTP

configurations will balance the traffic load, preventing wide scale disruptions when a single spanning tree instance fails. This will

allow for faster convergences of new topologies for the failed instance. Frames designated for these VLANs will be processed

quickly and completely throughout interconnected bridges utilizing any of the three spanning tree protocols (STP, RSTP or

MSTP).

This protocol will also tag BPDU packets so receiving devices can distinguish spanning tree instances, spanning tree regions and

the VLANs associated with them. An MSTI ID will classify these instances. MSTP will connect multiple spanning trees with a

Common and Internal Spanning Tree (CIST). The CIST will automatically determine each MSTP region, its maximum possible

extent and will appear as one virtual bridge that runs a single spanning tree. Consequentially, frames assigned to different VLANs

will follow different data routes within administratively established regions on the network, continuing to allow simple and full

processing of frames, regardless of administrative errors in defining VLANs and their respective spanning trees.

Each switch utilizing the MSTP on a network will have a single MSTP configuration that will have the following three attributes:

1. A configuration name defined by an alphanumeric string of up to 32 characters (defined in the MST Configuration

Identification window in the Configuration Name field).

2. A configuration revision number (named here as a Revision Level and found in the MST Configuration Identification

window) and;

3. A 4094-element table (defined here as a VID List in the MST Configuration Identification window), which will

associate each of the possible 4094 VLANs supported by the Switch for a given instance.

To utilize the MSTP function on the Switch, three steps need to be taken:

1. The Switch must be set to the MSTP setting (found in the STP Bridge Global Settings window in the STP Version

field)

2. The correct spanning tree priority for the MSTP instance must be entered (defined here as a Priority in the MSTI Config

Information window when configuring MSTI ID settings).

3. VLANs that will be shared must be added to the MSTP Instance ID (defined here as a VID List in the MST

Configuration Identification window when configuring an MSTI ID settings).

802.1D-2004 Rapid Spanning Tree

The Switch implements three versions of the Spanning Tree Protocol, the Multiple Spanning Tree Protocol (MSTP) as defined by

the IEEE 802.1Q-2005, the Rapid Spanning Tree Protocol (RSTP) as defined by the IEEE 802.1D-2004 specification and a

version compatible with the IEEE 802.1D-1998 STP. RSTP can operate with legacy equipment implementing IEEE 802.1D-1998;

however the advantages of using RSTP will be lost.

The IEEE 802.1D-2004 Rapid Spanning Tree Protocol (RSTP) evolved from the 802.1D-1998 STP standard. RSTP was

developed in order to overcome some limitations of STP that impede the function of some recent switching innovations, in

particular, certain Layer 3 functions that are increasingly handled by Ethernet switches. The basic function and much of the

terminology is the same as STP. Most of the settings configured for STP are also used for RSTP. This section introduces some

new Spanning Tree concepts and illustrates the main differences between the two protocols.

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D-Link DSA-3200 Technical Information Page 105

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D-Link DSA-3200 Technical Information Page 105

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