ITE PC v4.0 Chapter 1

Chapter 4: LAN RedundancySwitched Networks 2008 Cisco Systems, Inc. All rights reserved.Cisco ConfidentialPresentation_ID#Presentation_ID# 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential1Cisco Networking Academy programSwitched NetworksChapter 4: LAN Redundancy 2006, Cisco Systems, Inc. All rights reserved.Presentation_ID.scrChapter 44.0 Introduction4.1 Spanning Tree Concepts4.2 Varieties of Spanning Tree Protocols4.3 Spanning Tree Configuration4.4 First-Hop Redundancy Protocols4.5 SummaryPresentation_ID# 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential2Chapter 4 2006, Cisco Systems, Inc. All rights reserved.Presentation_ID.scrChapter 4: ObjectivesDescribe the issues with implementing a redundant network.Describe IEEE 802.1D STP operation.Describe the different spanning tree varieties.Describe PVST+ operation in a switched LAN environment.Describe Rapid PVST+ operation in a switched LAN environment.Configure PVST+ and Rapid PVST+ in a switched LAN environment.Identify common STP configuration issues.Describe the purpose and operation of first hop redundancy protocols.Describe the different varieties of first-hop redundancy protocols.Use Cisco IOS commands to verify HSRP and GLBP implementations.

Presentation_ID# 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential3 2006, Cisco Systems, Inc. All rights reserved.Presentation_ID.scr4.1 Spanning Tree Concepts

2008 Cisco Systems, Inc. All rights reserved.Cisco ConfidentialPresentation_ID#Presentation_ID# 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential44.1 Spanning Tree Concepts

2006, Cisco Systems, Inc. All rights reserved.Presentation_ID.scrPurpose of Spanning TreeRedundancy at OSI Layers 1 and 2

Presentation_ID# 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential4.1.1.1 Redundancy at OSI Layers 1 and 2

5 2006, Cisco Systems, Inc. All rights reserved.Presentation_ID.scrPurpose of Spanning TreeIssues with Layer 1 Redundancy: MAC Database InstabilityIf there is more than one path for the frame to be forwarded out, an endless loop can result. Ethernet frames do not have a Time to Live (TTL) attribute. Frames on a switched network, they continue to propagate between switches endlessly.This continued propagation between switches can result in MAC database instability.Presentation_ID# 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential4.1.1.2 Issues with Layer 1 Redundancy: MAC Database Instability6 2006, Cisco Systems, Inc. All rights reserved.Presentation_ID.scrPurpose of Spanning TreeIssues with Layer 1 Redundancy: Broadcast StormsSwitches will forward broadcast frames to all ports but the port the broadcast frame first entered the switch.If a Layer 2 loop is formed, broadcast frames are forwarded endlessly. This is called a broadcast storm. Consequently, no bandwidth is available for legitimate traffic and the network becomes unavailable for data communication. This is an effective denial of service.A broadcast storm is inevitable on a Layer 2 looped network.As more devices send broadcasts over the network, more traffic is caught within the loop, consuming resources. This eventually creates a broadcast storm that causes the network to fail.Presentation_ID# 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential4.1.1.3 Issues with Layer 1 Redundancy: Broadcast Storms

7 2006, Cisco Systems, Inc. All rights reserved.Presentation_ID.scrPurpose of Spanning TreeIssues with Layer 1 Redundancy: Duplicate Unicast FramesUnicast frames sent onto a looped network can result in duplicate frames arriving at the destination device.Most upper layer protocols are not designed to recognize, or cope with, duplicate transmissions. In general, protocols that make use of a sequence-numbering mechanism assume that the transmission has failed and that the sequence number has recycled for another communication session. Layer 2 LAN protocols, such as Ethernet, lack a mechanism to recognize and eliminate endlessly looping frames.Presentation_ID# 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential4.1.1.4 Issues with Layer 1 Redundancy: Duplicate Unicast Frames

8 2006, Cisco Systems, Inc. All rights reserved.Presentation_ID.scrSTP OperationSpanning-Tree Algorithm: IntroductionSTP ensures that there is only one logical path between all destinations on the network by intentionally blocking redundant paths that could cause a loop. A port is considered blocked when user data is prevented from entering or leaving that port. This does not include bridge protocol data unit (BPDU) frames that are used by STP to prevent loops. The physical paths still exist to provide redundancy, but these paths are disabled to prevent the loops from occurring. If the path is ever needed to compensate for a network cable or switch failure, STP recalculates the paths and unblocks the necessary ports to allow the redundant path to become active.Presentation_ID# 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential4.1.2.1 Spanning-Tree Algorithm: Introduction

9 2006, Cisco Systems, Inc. All rights reserved.Presentation_ID.scrSTP OperationSpanning-Tree Algorithm: Port Roles

Presentation_ID# 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential4.1.2.2 Spanning-Tree Algorithm: Port Roles

10 2006, Cisco Systems, Inc. All rights reserved.Presentation_ID.scrSTP OperationSpanning-Tree Algorithm: Root Bridge

Presentation_ID# 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential4.1.2.3 Spanning-Tree Algorithm: Root Bridge

11 2006, Cisco Systems, Inc. All rights reserved.Presentation_ID.scrSTP OperationSpanning-Tree Algorithm: Path Cost

Presentation_ID# 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential4.1.2.4 Spanning-Tree Algorithm: Path Cost

12 2006, Cisco Systems, Inc. All rights reserved.Presentation_ID.scrSTP Operation802.1D BPDU Frame Format

Presentation_ID# 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential4.1.2.5 802.1D BPDU Frame Format

13 2006, Cisco Systems, Inc. All rights reserved.Presentation_ID.scrSTP OperationBPDU Propagation and Process

Presentation_ID# 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential4.1.2.6 BPDU Propagation and Process

14 2006, Cisco Systems, Inc. All rights reserved.Presentation_ID.scrSTP OperationExtended System ID

Presentation_ID# 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential4.1.2.7 Extended System ID

15 2006, Cisco Systems, Inc. All rights reserved.Presentation_ID.scr4.2 Varieties of Spanning Tree Protocols

2008 Cisco Systems, Inc. All rights reserved.Cisco ConfidentialPresentation_ID#Presentation_ID# 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential164.2 Varieties of Spanning Tree Protocols

2006, Cisco Systems, Inc. All rights reserved.Presentation_ID.scrSTP OverviewList of Spanning Tree ProtocolsSTP or IEEE 802.1D-1998PVST+IEEE 802.1D-2004Rapid Spanning Tree Protocol (RSTP) or IEEE 802.1wRapid PVST+Multiple Spanning Tree Protocol (MSTP) or IEEE 802.1sPresentation_ID# 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential4.2.1.1 List of Spanning Tree Protocols

17 2006, Cisco Systems, Inc. All rights reserved.Presentation_ID.scrSTP OverviewSpanning Tree Protocol Characteristics

Presentation_ID# 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential4.2.1.2 Spanning Tree Protocol Characteristics

18 2006, Cisco Systems, Inc. All rights reserved.Presentation_ID.scrPVST+Overview of PVST+Networks running PVST+ have these characteristics:A network can run an independent IEEE 802.1D STP instance for each VLAN in the network.Optimum load balancing can result.One spanning-tree instance for each VLAN maintained can mean a considerable waste of CPU cycles for all switches in the network (in addition to the bandwidth used for each instance to send its own BPDU). Presentation_ID# 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential4.2.2.1 Overview of PVST+

19 2006, Cisco Systems, Inc. All rights reserved.Presentation_ID.scrPVST+Port States and PVST+ OperationSTP introduces the five port states:BlockingListeningLearningForwardingDisabledPresentation_ID# 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential4.2.2.2 Port States and PVST+ Operation

20 2006, Cisco Systems, Inc. All rights reserved.Presentation_ID.scrPVST+Extended System ID and PVST+ OperationIn a PVST+ environment, the extended switch ID ensures each switch has a unique BID for each VLAN.For example, the VLAN 2 default BID would be 32770 (priority 32768, plus the extended system ID of 2).

Presentation_ID# 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential4.2.2.3 Extended System ID and PVST+ Operation

21 2006, Cisco Systems, Inc. All rights reserved.Presentation_ID.scrRapid PVST+Overview of Rapid PVST+RSTP is the preferred protocol for preventing Layer 2 loops in a switched network environment. Cisco-proprietary enhancements to 802.1D, such as UplinkFast and BackboneFast, are not compatible with RSTP.RSTP (802.1w) supersedes STP (802.1D) while retaining backward compatibilityRSTP keeps the same BPDU format as IEEE 802.1D, except that the version field is set to 2 to indicate RSTP, and the flags field uses all 8 bits.RSTP is able to actively confirm that a port can safely transition to the forwarding state without relying on any timer configuration.Presentation_ID# 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential4.2.3.1 Overview of Rapid PVST+

22 2006, Cisco Systems, Inc. All rights reserved.Presentation_ID.scrRapid PVST+RSTP BPDU

Presentation_ID# 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential4.2.3.2 RSTP BPDU

23 2006, Cisco Systems, Inc. All rights reserved.Presentation_ID.scrRapid PVST+Edge Ports

Presentation_ID# 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential4.2.3.3 Edge Ports

24 2006, Cisco Systems, Inc. All rights reserved.Presentation_ID.scrRapid PVST+Link Types

Presentation_ID# 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential4.2.3.4 Link Types

25 2006, Cisco Systems, Inc. All rights reserved.Presentation_ID.scr4.3 Spanning Tree Configuration

2008 Cisco Systems, Inc. All rights reserved.Cisco ConfidentialPresentation_ID#Presentation_ID# 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential264.3 Spanning Tree Configuration

2006, Cisco Systems, Inc. All rights reserved.Presentation_ID.scrPVST+ ConfigurationCatalyst 2960 Default Configuration

Presentation_ID# 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential4.3.1.1 Catalyst 2960 Default Configuration

27 2006, Cisco Systems, Inc. All rights reserved.Presentation_ID.scrPVST+ ConfigurationConfiguring and Verifying the Bridge ID

Presentation_ID# 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential4.3.1.2 Configuring and Verifying the Bridge ID

28 2006, Cisco Systems, Inc. All rights reserved.Presentation_ID.scrPVST+ ConfigurationPortFast and BPDU Guard

Presentation_ID# 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential4.3.1.3 PortFast and BPDU Guard

29 2006, Cisco Systems, Inc. All rights reserved.Presentation_ID.scrPVST+ ConfigurationPVST+ Load Balancing

Presentation_ID# 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential4.3.1.4 PVST+ Load Balancing

30 2006, Cisco Systems, Inc. All rights reserved.Presentation_ID.scrRapid PVST+ ConfigurationSpanning-Tree Mode

Presentation_ID# 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential4.3.2.1 Spanning-Tree Mode

31 2006, Cisco Systems, Inc. All rights reserved.Presentation_ID.scrSTP Configuration IssuesAnalyzing the STP Topology

Presentation_ID# 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential4.3.3.1 Analyzing the STP Topology

32 2006, Cisco Systems, Inc. All rights reserved.Presentation_ID.scrSTP Configuration IssuesExpected Topology vs. Actual Topology

Presentation_ID# 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential4.3.3.2 Expected Topology vs. Actual Topology

33 2006, Cisco Systems, Inc. All rights reserved.Presentation_ID.scrSTP Configuration IssuesOverview of Spanning-Tree Status

Presentation_ID# 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential4.3.3.3 Overview of Spanning-Tree Status

34 2006, Cisco Systems, Inc. All rights reserved.Presentation_ID.scrSTP Configuration IssuesSpanning-Tree Failure Consequences

Presentation_ID# 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential4.3.3.4 Spanning-Tree Failure Consequences

35 2006, Cisco Systems, Inc. All rights reserved.Presentation_ID.scrSTP Configuration IssuesRepairing a Spanning-Tree ProblemOne way to correct spanning-tree failure is to manually remove redundant links in the switched network, either physically or through configuration, until all loops are eliminated from the topology.Before restoring the redundant links, determine and correct the cause of the spanning-tree failure. Carefully monitor the network to ensure that the problem is fixed.Presentation_ID# 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential4.3.3.5 Repairing a Spanning-Tree Problem

36 2006, Cisco Systems, Inc. All rights reserved.Presentation_ID.scr4.4 First-Hop Redundancy Protocols

2008 Cisco Systems, Inc. All rights reserved.Cisco ConfidentialPresentation_ID#Presentation_ID# 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential374.4 First-Hop Redundancy Protocols

2006, Cisco Systems, Inc. All rights reserved.Presentation_ID.scrConcept of First-Hop Redundancy ProtocolsDefault Gateway Limitations

Presentation_ID# 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential4.4.1.1 Default Gateway Limitations38 2006, Cisco Systems, Inc. All rights reserved.Presentation_ID.scrConcept of First-Hop Redundancy ProtocolsRouter Redundancy

Presentation_ID# 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential4.4.1.2 Router Redundancy

39 2006, Cisco Systems, Inc. All rights reserved.Presentation_ID.scrConcept of First-Hop Redundancy ProtocolsSteps for Router Failover

Presentation_ID# 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential4.4.1.3 Steps for Router Failover

40 2006, Cisco Systems, Inc. All rights reserved.Presentation_ID.scrVarieties of First-Hop Redundancy ProtocolsFirst-Hop Redundancy ProtocolsHot Standby Router Protocol (HSRP)HSRP for IPv6Virtual Router Redundancy Protocol version 2 (VRRPv2)VRRPv3Gateway Load Balancing Protocol (GLBP)GLBP for IPv6 ICMP Router Discovery Protocol (IRDP)Presentation_ID# 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential4.4.2.1 First-Hop Redundancy Protocols

41 2006, Cisco Systems, Inc. All rights reserved.Presentation_ID.scrFHRP VerificationHSRP Verification

Presentation_ID# 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential4.4.3.1 HSRP Verification

42 2006, Cisco Systems, Inc. All rights reserved.Presentation_ID.scrFHRP VerificationGLBP Verification

Presentation_ID# 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential4.4.3.2 GLBP Verification

43 2006, Cisco Systems, Inc. All rights reserved.Presentation_ID.scr4.5 Summary

2008 Cisco Systems, Inc. All rights reserved.Cisco ConfidentialPresentation_ID#Presentation_ID# 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential444.5 Summary

2006, Cisco Systems, Inc. All rights reserved.Presentation_ID.scrChapter 4: SummaryIEEE 802.1D is implemented on Cisco switches on a per-VLAN basis in the form of PVST+. This is the default configuration on Cisco switches.RSTP can be implemented on Cisco switches on a per-VLAN basis in the form of Rapid PVST+.With PVST+ and Rapid PVST+, root bridges can be proactively configured to enable spanning tree load balancing.First-hop redundancy protocols, such as HSRP, VRRP, and GLBP provide alternate default gateways for hosts in the switched environment.

Presentation_ID# 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential45Chapter 4 Summary 2006, Cisco Systems, Inc. All rights reserved.Presentation_ID.scr

Presentation_ID# 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential