Juniper JUNOS OS 10.3 - SOFTWARE Manual page 1670

Complete Software Guide for Junos
Requirements
Overview and Topology
1574
®
OS for EX Series Ethernet Switches, Release 10.3
Configuration on page 1576
Verification on page 1576
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.
When root protection is enabled on an interface:
The interface is blocked from becoming the root port.
Root protection is enabled for all 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.
CAUTION: An interface can be configured for either root protection or loop
protection, but not for both.
Four EX Series switches are displayed in Figure 40 on page 1575. In this example, they are
configured for RSTP and create a loop-free topology. Interface
a designated port on an administrative boundary. It connects to Switch 4. Switch 3 is the
root bridge. Interface
ge-0/0/6
on Switch 1 is the root port.
Copyright © 2010, Juniper Networks, Inc.
on Switch 1 is
ge-0/0/7