Example: Configuring Loop Protection To Prevent Interfaces From Transitioning From Blocking To Forwarding In A Spanning Tree On Ex Series Switches - Juniper EX9200 Features Manual

Spanning-Tree Protocols Feature Guide for EX9200 Switches
Example: Configuring Loop Protection to Prevent Interfaces from Transitioning from
Blocking to Forwarding in a Spanning Tree on EX Series Switches
Requirements
Overview and Topology
234
NOTE: This example uses Junos OS for EX Series switches with support for
the Enhanced Layer 2 Software (ELS) configuration style. If your switch runs
software that does not support ELS, see Example: Configuring Loop Protection
to Prevent Interfaces from Transitioning from Blocking to Forwarding in a
Spanning Tree on EX Series Switches. For ELS details, see Getting Started with
Enhanced Layer 2 Software.
EX Series switches provide Layer 2 loop prevention through Spanning Tree Protocol
(STP), Rapid Spanning Tree protocol (RSTP), and Multiple Spanning Tree Protocol
(MSTP). Loop protection increases the efficiency of STP, RSTP, and MSTP by preventing
interfaces from moving into a forwarding state that would result in a loop opening up in
the network.
This example describes how to configure loop protection for an interface on an EX Series
switch in an RSTP topology:
Requirements on page 234
Overview and Topology on page 234
Configuration on page 236
Verification on page 236
This example uses the following software and hardware components:
Junos OS Release 13.2X50-D10 or later or later for EX Series switches
Three EX Series switches in an RSTP topology
Before you configure the interface for loop protection, be sure you have:
RSTP operating on the switches.
NOTE: By default, RSTP is enabled on all EX Series switches.
A loop-free network in spanning-tree topologies 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 (preventing loops) and which
interfaces become root ports and forward traffic.
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