Spanning Tree - D-Link xStack DES-3200 Series Reference Manual

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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).
xStack® DES-3200 Series Layer 2 Managed Fast Ethernet Switch
Use the drop-down menus to select a range of ports to use in the configuration.
Specify the type of the ports.
UNI - Specify the ports as UNI ports.
NNI - Specify the ports as NNI ports.
None - Disable tunnel on it.
Specify tunneled protocols on the UNI ports.
STP - Specify to use the STP protocol.
GVRP - Specify to use the GVRP protocol.
Protocol MAC - Specify the destination MAC address of the L2 protocol packets that will
tunneled on these UNI ports. The MAC address can be 01-00-0C-CC-CC-CC or 01-00-
0C-CC-CC-CD.
All - All tunnel enabled Layer 2 protocols will be tunneled on the ports.
Specify the drop threshold for packets-per-second accepted on the UNI ports. The ports
drop the PDU if the protocol's threshold is exceeded.
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