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Configuring MST Instances on a Physical Interface

You can configure a Multiple Spanning-Tree Instance (MSTI) under the following hierarchy levels:

Before you begin, configure Multiple Spanning-Tree Protocol. For configuration details, see Configuring MSTP.

Enable configuration of a MST instance:
[edit] user@host# edit ... protocols mstp msti msti-id
The msti-id value must be from 1 through 64.
Configure the interfaces that participate in the MST instance.
1. Enable configuration of the interface:
  [edit ... protocols mstp msti msti-id] user@host# edit interface interface-name
2. Configure the interface priority:
  [edit ... protocols mstp msti msti-id interface interface-name] user@host# set priority interface-priority
3. (Optional) Configure the interface as an edge port:
  [edit ... protocols mstp msti msti-id interface interface-name] user@host# set edge
Configure the bridge priority
[edit ... protocols mstp msti msti-id] user@host# set bridge-priority bridge-priority
For more information, see Understanding Bridge Priority for Election of Root Bridge and Designated Bridge.
(Optional) An MSTI can map to a range of VLANs just as a logical port can map to a range of VLANs. The MSTP VLAN specifies the VLAN or VLAN range to which this MSTI is mapped. The vlan-id is configured under the logical interface. Configure the VLAN or VLAN range of the MSTI instance:
[edit] user@host# set vlan (vlan-id | vlan-id-range)
Verify the MST interface configuration.
[edit]
protocols {
mstp {
...basic-mstp-configuration...
msti msti-id { # Instance identifier 1 – 64.
bridge-priority priority;
vlan vlan-id; # Optional
interface interface-name {
cost cost;
edge;
priority interface-priority;
}
}
}
}

Note: All STP ports on a bridge domain must belong to the same MST (multiple spanning tree) instance.