• cost
• edge
• interface (Spanning Tree)
• mode
• priority
Spanning-Tree Instance Interface Priority
The root port is the interface on the nonroot bridge with the lowest path cost to the root
bridge. When multiple interfaces have the same path cost to the root bridge, the interface
with the lowest interface priority is selected as the root port.
If the interface priority is not configured and multiple interfaces have the same path cost
to the root bridge, the interface with the lowest interface identifier is selected as the root
port.
If the interface priority is configured under the MSTP protocol, this becomes the default
value for all interfaces. If the interface priority is configured under the MSTI interface, the
value overrides the default for that interface.
If the interface priority is configured at both the VSTP global and VLAN levels, the
configuration at the VLAN level overrides the global configuration.
Related
Documentation
Configuring Rapid Spanning Tree Protocol•
• Configuring Multiple Spanning Tree Protocol
• Configuring VLAN Spanning Tree Protocol
• interface (Spanning Tree)
• priority
Spanning-Tree Instance Interface Cost
The path cost used to calculate the root path cost from any given LAN segment is
determined by the total cost of each link in the path. By default, the link cost is determined
by the speed of the link. The interface cost can be configured to override the default cost
and control which bridge is the designated bridge and which port is the designated port.
In MSTP the CIST external path cost is determined by the link speed and the number of
hops.
If the interface cost is not configured, the cost is determined by the speed of the interface.
For example, a 100-Mbps link has a default path cost of 19, a 1000-Mbps link has a default
path cost of 4, and a 10-Gbps link has a default path cost of 2.
Copyright © 2017, Juniper Networks, Inc.408
ACX Series Universal Access Router Configuration Guide
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