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DGS-3600 Series Layer 3 Gigabit Ethernet Managed Switch CLI Manual
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MULTIPLE SPANNING TREE PROTOCOL (MSTP) COMMANDS
This Switch supports three versions of the Spanning Tree Protocol; 802.1D STP, 802.1D 2004 RSTP, 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 either 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. These instances will
be classified by an instance_id. 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:
A configuration name defined by an alphanumeric string of up to 32 characters (defined in the config stp mst_config_id
command as name <string>).
A configuration revision number (named here as a revision_level) and;
A 4096 element table (defined here as a vid_range) which will associate each of the possible 4096 VLANs supported by
the Switch for a given instance.
To utilize the MSTP function on the Switch, three steps need to be taken:
• The Switch must be set to the MSTP setting (config stp version)
• The correct spanning tree priority for the MSTP instance must be entered (config stp priority).
• VLANs that will be shared must be added to the MSTP Instance ID (config stp instance_id).
The Multiple Spanning Tree Protocol (MSTP) commands in the Command Line Interface (CLI) are listed (along with the
appropriate parameters) in the following table.