Bridge Priority For Election Of Root Bridge And Designated Bridge; Maximum Age For Awaiting Arrival Of Hello Bpdus - Juniper ACX1000 Configuration Manual

ACX Series Universal Access Router Configuration Guide

Bridge Priority for Election of Root Bridge and Designated Bridge

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Maximum Age for Awaiting Arrival of Hello BPDUs

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Documentation
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Use the bridge priority to control which bridge is elected as the root bridge and also to
control which bridge is elected the root bridge when the initial root bridge fails.
The root bridge for each spanning-tree protocol instance is determined by the bridge ID.
The bridge ID consists of a configurable bridge priority and the MAC address of the bridge.
The bridge with the lowest bridge ID is elected as the root bridge. If the bridge priorities
are equal or if the bridge priority is not configured, the bridge with the lowest MAC address
is elected the root bridge.
The bridge priority can also be used to determine which bridge becomes the designated
bridge for a LAN segment. If two bridges have the same path cost to the root bridge, the
bridge with the lowest bridge ID becomes the designated bridge.
The bridge priority can be set only in increments of 4096.
Consider a sample scenario in which a dual-homed customer edge (CE) router is
connected to two other provider edge (PE) routers, which function as the VPLS PE routers,
with MTSP enabled on all these routers, and with the CE router operating as the root
bridge. Integrated Routing and Bridging (IRB) interface is configured for the VPLS routing
instances on the routers. In such a network, the MAC addresses that are learned in the
VPLS domain continuously move between the LSI or virtual tunnel (VT) interfaces and
the VPLS interfaces on both the PE routers. To avoid the continuous movement of the
MAC addresses, you must configure root protection by including the
statement at the [edit routing-instances routing-instance-name protocols mstp interface
hierarchy level and configure the bridge priority as zero by including the
interface-name]
statement at the
bridge priority 0
mstp] hierarchy level on the PE routers. This configuration on the PE routers is required
to prevent the CE-side facing interfaces from becoming the root bridge.
Configuring Rapid Spanning Tree Protocol
Configuring Multiple Spanning Tree Protocol
Configuring VLAN Spanning Tree Protocol
bridge-priority
The maximum age timer specifies the maximum expected arrival time of hello BPDUs.
If the maximum age timer expires, the bridge detects that the link to the root bridge has
failed and initiates a topology reconvergence. The maximum age timer should be longer
than the configured hello timer.
Configuring Rapid Spanning Tree Protocol
Configuring Multiple Spanning Tree Protocol
[edit routing-instances routing-instance-name protocols
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