Specifications

DGS-3048 Layer 2 Switch CLI Reference Manual
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MULTIPLE SPANNING TREE PROTOCOL (MSTP)
COMMANDS
This switch supports three versions of the Spanning Tree Protocol; 802.1d STP, 802.1w Rapid STP and 802.1s
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
BDPU 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) 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>).
b) A configuration revision number (named here as a revision_level) and;
c) 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:
a) The Switch must be set to the MSTP setting (config stp version)
b) The correct spanning tree priority for the MSTP instance must be entered (config stp priority).
c) VLANs that will be shared must be added to the MSTP Instance ID (config stp instance_id).
The Multiple Spanning Tree Protocol commands in the Command Line Interface (CLI) are listed (along with the
appropriate parameters) in the following table.
Command Parameters
enable stp
disable stp
config stp version [mstp | rstp | stp]
config stp {maxage <value 6-40> | maxhops <value 1-20> | hellotime <value
1-10> | forwarddelay <value 4-30>| fbpdu [enable | disable]}
config stp ports <portlist> {externalCost [auto | <value 1-200000000>] | edge [true
| false] | p2p [true | false | auto ] | state [enable | disable]}
config stp instance _id <value 1-15> [add_vlan | remove_vlan] <vidlist>
config stp priority <value 0-61440> instance_id <value 0-15>
config stp {revision_level <int 0-65535> | name <string>}