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VRRP: Increasing Reliability and Failover with the Virtual Router Redundancy Protocol

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VRRP: Increasing Reliability and Failover with the Virtual Router Redundancy Protocol


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  • Copyright 2003
  • Edition: 1st
  • Book
  • ISBN-10: 0-201-71500-7
  • ISBN-13: 978-0-201-71500-2

"A detailed and clearly written book that is an invaluable resource to all VRRP users and implementers."
--Scott Bradner, Senior Technical Consultant, Harvard University

By employing the Virtual Router Redundancy Protocol (VRRP), administrators can ensure that their networks remain up and running, thereby eliminating expensive downtime. Using VRRP to avoid network outages is essential to building accessible, robust networks, and central to the implementation of successful disaster recovery models. Written by experts who contributed to the design of the VRRP protocol and participated actively in its deployment, VRRP: Increasing Reliability and Failover with the Virtual Router Redundancy Protocol is your best introduction to this powerful high-availability tool.

VRRP examines the general characteristics of the protocol and its usage. The emphasis is on translating the protocol specification into a tutorial form ideal for day-to-day users of VRRP. In addition to introducing the technology, this book provides an in-depth analysis, featuring extensive material on configuring, managing, and troubleshooting VRRP. Precursors to this protocol, such as Cisco's HSRP and DEC's IPSTP, are also discussed. Various vendor-specific extensions to VRRP--and their use in solving specific high-availability problems not addressed by VRRP--are also examined.

Network administrators and managers, protocol implementers, practicing professionals, researchers, and students exploring the area of high availability will gain a solid understanding of the core concepts of reliability and redundancy based on VRRP, as well as the particulars of the VRRP protocol and how to implement it.

The appendixes provide the necessary background for networking and TCP/IP, the full text of VRRP MIB, a study of actual VRRP implementations and an analysis of public-domain software available for VRRP over Linux, an overview of the VRRP state machine using SDL flowcharts and UML diagrams, and an analysis of the protocol through formal logic.


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Table of Contents




1. Networking, Availability, and VRRP.

Availability and Networking.

Networking and Availability.

Virtual Router Redundancy.


2. VRRP Overview.

The Case for VRRP.

Basic Concepts and Configurations.

Load Sharing.

Multiple Backups.


Virtual Routers Without Owner.

One Backup Protecting Two Masters.

Virtual Routers with Multiple IP Addresses.

Failure Cases.

A Few Words About Router Virtuality.

Case Studies.



3. VRRP Messages.

Message Format.

Message Exchange.

Sniffed Data from VRRP Messages.


4. VRRP in Action.

VRRP State Machine.

VRRP State Machine in Motion.

VRRP Operations.


5. VRRP and Network Technologies.

VRRP over Ethernet.

VRRP and Learning Bridges.


VRRP over Token Ring.



6. VRRP and VPNs.

VRRP and Firewalls.

VRRP and Tunnels.

Trade-Offs in VPN Availability.



7. SNMP Management.

VRRP MIB Organization.

Illustrative Cases.

A Closer Look at the VRRP Operations Table.

Configuring VRRP Operation Tables.

Associated IP Address Table.

A Pseudo Command Set for VRRP Configurations.

VRRP Statistics.

VRRP Notifications.

Browsing SNMP MIB.

SNMP Management of VRRP: Operational Issues.


8. VRRP Configuration and Craft Person Interface.

CLI Hierarchy.

Configuration of CLI Commands.

Basic VRRP Configuration.

Monitoring and Troubleshooting Using CLI.


9. VRRP Configuration Using a Graphical User Interface.

Nortel Networks' Site Manager.

Configuring VRRP on Nortel Networks Contivity Extranet Switch.

Nortel Networks' Accelar Device Manager.

Monitoring VRRP Using HP Openview.



10. Precursors to VRRP.

Cisco's HSRP.

Digital Equipment Corporation's IP Standby Protocol.


11. Future of VRRP.

Extensions to VRRP.

VRRP for Advanced High Availability.

Future of VRRP: VRRP and IPv6.

Future of High Availability: Clustering and Beyond.



Appendix A. Networking and TCP/IP Overview.

Layering the Network.

Forwarding the Data.

Controlling the Network.

Securing the Network.

Managing the Network.

Appendix B. VRRP MIB (from RFC 2787).
Appendix C. VRRP in the Public Domain.
Appendix D. SDL Overview and Flowcharts for VRRP.

Graphical Representations.

VRRP State Machine Transitions.

Appendix E. VRRP from a Logical Point of View.

Approach and Notation.

Logical Laws and Equivalences Used in the Discussions.

About Our Formal Perspective.


Protocol Assertions.

Explications for State Machine.


List of Symbolic Assertions and Norms.

Appendix F. UML Overview and Diagrams for VRRP.

State Diagrams.

Sequence Diagrams.

VRRP State Diagram.

VRRP Sequence Diagram.

Index. 0201715007T09052002


With the explosion of the Internet, computers have become ubiquitous and the networks to connect them have become as pervasive and as critical as a telephone connection. Many businesses depend on their networks to conduct their day-to-day operations, to offer their services and often times to sell their products. Further, the global reach of the Internet crossing language and geographic barriers has resulted in businesses needing to be open to serve one part of the world while the other part sleeps. Consequently, it has become critical for networks to be up and available 24 hours a day, seven days a week to serve a global customer base.

Network failures result in losses of hundreds of millions of dollars to businesses each year. These network failures can happen as a result of failure of a single network device or because of a disaster striking the area where the key network devices are housed. According to a study by a major analyst group, the network outages may cost a business up to $200,000 per minute. The stakes may even be higher than the monetary damage. Here is a good way to relate to the impact of unavailability: A user may be satisfied with 99.9% availability of his network. But 0.1% unavailability can be very damaging in other contexts. The following list highlights the potential impact if the availability was only 99.9%:

  • 12 newborns would be given to the wrong parents each day.
  • 291 pacemaker operations would be performed incorrectly.
  • 315 entries in Webster's Dictionary would be misspelled.
  • 3056 copies of tomorrow's Wall Street Journal would be missing one of the three sections.
  • 18,322 pieces of mail would be mishandled every hour.
  • 20,000 incorrect drug prescriptions would be written each year.
  • 103,260 income tax returns will be processed incorrectly during the year. (Please not mine unless it results in a big refund!)
  • 114,500 mismatched pairs of shoes would be shipped each year.
  • 880,000 credit cards would have incorrect cardholder information on their magnetic strips.
  • 2.5 million books would be shipped with the wrong covers.
  • 5.5 million cases of soft drinks produced would be flat.

Scary, isn't it? A very convincing argument for taking network availability seriously since it may very well be the foundation for any one of the listed situations.

For the Internet to preserve its vital status for the business, every part of the Internet needs to be robust and every network attached to the Internet must be reachable at all times. As a result, high availability, redundancy, traffic sharing and disaster recovery have become major concerns, a high priority for network professionals determined to build accessible, robust networks

There are several aspects to building a robust and reliable network that can survive a large-scale disaster, component, link, and device failures. One important technique in achieving this goal has been to build networks with redundant physical components and associated protocols that let the components, appear as a single entity to the rest of the network while sharing the network traffic load. Virtual Router Redundancy Protocol (VRRP) is such a protocol that enables multiple physical routers to appear as a single entity to the hosts on the network even when they are physically away from each other, thereby avoiding loss of network availability in case of disaster or a router failure and removing the need for cumbersome reconfiguration of hosts.


This book presents VRRP, one of the instruments in the toolkit of a network administrator used for dealing with certain aspects of network availability, disaster recovery and redundancy, namely the challenges of keeping the network services available to the hosts attached to a LAN during times of network failures. The book gives an overview of VRRP by discussing a series of configuration examples and deployment scenarios and describing the specific details of protocol implementation for various types of LAN technologies. The main objectives of the book are as follows:

  • To describe the general characteristics of VRRP and its usage over various LAN technologies with an emphasis on translating the protocol specification into a tutorial form for ease of understanding by the day-to-day users of VRRP such as network administrators, engineers tasked with implementing the protocol for a commercial product and students interested in high availability.
  • To provide sufficient background material so that this book is self-contained and can be read without the need for other refresher books for LAN and IP technologies.
  • To discuss real-life deployment scenarios, security and management issues related to the usage of VRRP while articulating the high availability problems that are not solved by VRRP.


The book is organized into four parts: Introduction and VRRP overview; Detailed Analysis of VRRP; Configuring, managing, and troubleshooting VRRP; and VRRP Precursors, Extensions and Futures. The book has an additional Appendix section.

  • Part I consists of Chapters 1 and 2. Chapter 1 deals with the introduction to Availability and a general overview of networking in the context of availability. Chapter 2 outlines the problems not solved by technologies prior to VRRP and provides a overview and explanation of VRRP concepts using various deployment examples.
  • Part II comprises Chapters 3,4,5 and 6. Chapter 3 describes the various VRRP messages and protocol exchange in detail and provides real life packet captures of VRRP packets to get familiarized with the protocol for network administrators. Chapter 4 dives into the gut of the VRRP state machine and provides a detailed discussion of VRRP in action in various deployment scenarios. In Chapter 5, we focus on VRRP over various LAN technologies such as Ethernet, Token Ring, FDDI and ATM LANE. This section discusses the implementation issues and differences with VRRP in the context of these LAN technologies. Finally, Chapter 6 touches upon VRRP in the presence of Virtual Private Networks (VPNs)
  • Part III spans Chapters 7 through 9. Chapter 7 focuses on the VRRP MIB and SNMP. Chapter 8 provides various vendor configurations using Command Line Interface (CLI) and provides a detailed discussion of VRRP configuration and troubleshooting with various vendor devices and outlines the actual CLI commands and error messages with deployment examples. Chapter 9 focuses on configuration and monitoring of various vendor devices using the Graphical User Interface (GUI).
  • Part IV includes Chapters 10 and 11. Chapter 10 focuses on the pre-cursors to VRRP in the arena of High Availability and discusses Cisco's HSRP and DECs IPSTB Protocols. A table of comparison of benefits between VRRP and these protocols is also provided. Chapter 11 wraps up with a look at various vendor specific extensions to VRRP to solve specific problems not solved by VRRP and looks into the crystal ball to the future of high availability such as VRRP and Mobile IP, IPv6 and Clustering.
  • The Appendix Section is comprised of 6 Appendixes. Appendix A is an extensive tutorial/refresher on Layering, OSI layering, Layer 2 technologies, and Layer 3 technologies. It also provides a refresher on Network Management and Security. Appendix B contains the exact VRRP MIB from RFC 2787. Appendix C contains an example of an actual public domain implementation of VRRP in C programming language with explanations of what each code segment does. Appendix D contains Specification and Description Language (SDL) and flow chart implementations of the VRRP state machine. Appendix E looks at VRRP Protocol description from a formal logic perspective and uses predicate calculus and deontic logic to explain the protocol. Finally, Appendix F implements the VRRP state machine using the Unified Modeling Language (UML).


This book targets a broad range of readers interested in redundancy and high availability and the use of network protocols to provide redundancy and high availability:

Network Administrators and managers: This book gives an overview of high availability issues and how VRRP specifically contributes to ensuring high availability in the LAN segment. This book contains numerous examples of network configurations using VRRP and ways in which to monitor and debug VRRP. The book further illustrates various practical network configurations, issues, and gotchas with manageability. It provides GUI and CLI configuration examples of various vendors of VRRP that the reader can use right away. This book also highlights the problems that are not solved by VRRP, thereby creating awareness for the need for other tools to complement this protocol.
Target Sections: Part I, Part III, and Part IV with Part II and Appendix II as reference material. Appendix A would be useful as refresher material.
Protocol Implementers: This book details the innards of the VRRP RFC by using different representational techniques such as state machines, SDL flow charts, and UML sequence diagrams for easy understanding of the protocol. It points out critical design issues that development engineers may encounter while implementing the protocol. The Appendixes further explain the formal aspects of the protocol for the expert reader and contains concise background material on SDL and UML. A public domain VRRP implementation is also discussed in detail with a detailed walk through of the source code.
Target Sections: Part I, Part II, and Part IV, Appendices B, C, D, and F with Chapter 7 as reference material.
Students, Researchers, and Professionals exploring the area of High Availability: With its full set of appendices, this book is fairly self contained, encompassing an overview section of basic TCP/IP concepts required for understanding VRRP and providing a detailed and simple explanation of VRRP in its overview chapters.
Target Sections: Entire book starting with Appendices as needed.



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