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.
Overview and Topology
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.
A blocking interface can transition to the forwarding state in error if the interface stops
receiving BPDUs from its designated port on the segment. Such a transition error can
occur when there is a hardware error on the switch or software configuration error between
the switch and its neighbor. When this happens, a loop opens up in the spanning tree.
Loops in a Layer 2 topology cause broadcast, unicast, and multicast frames to
continuously circle the looped network. As a switch processes a flood of frames in a
looped network, its resources become depleted and the ultimate result is a network
outage.
CAUTION:
An interface can be configured for either loop protection or root
protection, but not for both.
Three EX Series switches are displayed in Figure 39 on page 1571. In this example, they are
configured for RSTP and create a loop-free topology. Interface
ge-0/0/6
is blocking
traffic between Switch 3 and Switch 1; thus, traffic is forwarded through interface
ge-0/0/7
on Switch 2. BPDUs are being sent from the root bridge on Switch 1 to both of these
interfaces.
This example shows how to configure loop protection on interface
ge-0/0/6
to prevent
it from transitioning from a blocking state to a forwarding state and creating a loop in
the spanning-tree topology.
Copyright © 2010, Juniper Networks, Inc.
1570
Complete Software Guide for Junos
®
OS for EX Series Ethernet Switches, Release 10.3
Summary of Contents for JUNOS OS 10.3 - SOFTWARE
Page 325: ...CHAPTER 17 Operational Mode Commands for System Setup 229 Copyright 2010 Juniper Networks Inc ...
Page 1323: ...CHAPTER 56 Operational Mode Commands for Interfaces 1227 Copyright 2010 Juniper Networks Inc ...
Page 2841: ...CHAPTER 86 Operational Commands for 802 1X 2745 Copyright 2010 Juniper Networks Inc ...
Page 3367: ...CHAPTER 113 Operational Mode Commands for CoS 3271 Copyright 2010 Juniper Networks Inc ...
Page 3435: ...CHAPTER 120 Operational Mode Commands for PoE 3339 Copyright 2010 Juniper Networks Inc ...
Page 3529: ...CHAPTER 126 Operational Mode Commands for MPLS 3433 Copyright 2010 Juniper Networks Inc ...