Understanding Root Protection For Stp, Rstp, Vstp, And Mstp On Ex Series Switches - Juniper EX9200 Features Manual

Understanding Root Protection for STP, RSTP, VSTP, and MSTP on EX Series Switches

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Copyright © 2017, Juniper Networks, Inc.
Juniper Networks EX Series Ethernet Switches provide Layer 2 loop prevention through
Spanning Tree Protocol (STP), Rapid Spanning Tree Protocol (RSTP), VLAN Spanning
Tree Protocol (VSTP), and Multiple Spanning Tree Protocol (MSTP). A loop-free network
is supported through the exchange of a special type of frame called bridge protocol data
unit (BPDU). Peer STP applications running on the switch interfaces use BPDUs to
communicate. Ultimately, the exchange of BPDUs determines which interfaces block
traffic and which interfaces become root ports and forward traffic.
However, a root port elected through this process has the possibility of being wrongly
elected. A user bridge application running on a PC can generate BPDUs, too, and interfere
with root port election. Root protection allows network administrators to manually
enforce the root bridge placement in the network.
Enable root protection on interfaces that must not receive superior BPDUs from the root
bridge and must not be elected as the root port. These interfaces become designated
ports and are typically located on an administrative boundary. If the bridge receives
superior STP BPDUs on a port that has root protection enabled, that port transitions to
a root-prevented STP state (inconsistency state) and the interface is blocked. This
blocking prevents a bridge that should not be the root bridge from being elected the root
bridge. After the bridge stops receiving superior STP BPDUs on the interface with root
protection, the interface returns to a listening state, followed by a learning state, and
ultimately back to a forwarding state. Recovery back to the forwarding state is automatic.
When root protection is enabled on an interface, it is enabled for all the STP instances
on that interface. The interface is blocked only for instances for which it receives superior
BPDUs. Otherwise, it participates in the spanning-tree topology.
An interface can be configured for either root protection or loop protection, but not for
both.
Configuring BPDU Protection on Spanning Tree Interfaces on page 230
Example: Configuring Root Protection to Enforce Root Bridge Placement in Spanning
Trees on EX Series Switches
Example: Configuring Loop Protection to Prevent Interfaces from Transitioning from
Blocking to Forwarding in a Spanning Tree on EX Series Switches
Example: Configuring BPDU Protection on Edge Interfaces to Prevent STP Miscalculations
on EX Series Switches
Example: Configuring BPDU Protection on Interfaces to Prevent STP Miscalculations on
EX Series Switches
Understanding MSTP for EX Series and QFX Series Switches on page 78
Understanding RSTP for EX Series and QFX Series Switches on page 3
Understanding STP for EX Series Switches
Understanding VSTP for EX Series Switches and QFX Series Switches on page 159
Chapter 10: Using BPDU Protection, Root Protection, and Loop Protection
233