Juniper JUNOS OS 10.4 - FOR EX REV 1 Manual page 1911

Example: Configuring Root Protection to Enforce Root Bridge Placement in Spanning
Trees on EX Series Switches
Requirements
Overview and Topology
Copyright © 2010, Juniper Networks, Inc.
Understanding Loop Protection for STP, RSTP, VSTP, and MSTP on EX Series Switches
on page 1758
EX Series switches provide Layer 2 loop prevention through Spanning Tree Protocol
(STP), Rapid Spanning Tree protocol (RSTP), and Multiple Spanning Tree Protocol
(MSTP). Root protection increases the efficiency of STP, RSTP, and MSTP by allowing
network administrators to manually enforce the root bridge placement in the network.
This example describes how to configure root protection on an interface on an EX Series
switch:
Requirements on page 1807
Overview and Topology on page 1807
Configuration on page 1810
Verification on page 1810
This example uses the following hardware and software components:
Junos OS Release 9.1 or later for EX Series switches
Four EX Series switches in an RSTP topology
Before you configure the interface for root protection, be sure you have:
RSTP operating on the switches.
NOTE: By default, RSTP is enabled on all EX Series switches.
Peer STP applications running on switch interfaces exchange a special type of frame
called a bridge protocol data unit (BPDU). Switches communicate interface information
using BPDUs to create a loop-free topology that ultimately determines the root bridge
and which interfaces block or forward traffic in the spanning tree.
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.
To prevent this from happening, enable root protection on interfaces that should not
receive superior BPDUs from the root bridge and should not be elected as the root port.
These interfaces are typically located on an administrative boundary and are designated
ports.
Chapter 71: Examples of Spanning-Tree Protocols Configuration
1807