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Optimal Routing Design

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  • Description
  • Sample Content
  • Updates
  • Copyright 2005
  • Dimensions: 7-3/8" x 9-1/8"
  • Edition: 1st
  • eBook (Watermarked)
  • ISBN-10: 0-13-344710-3
  • ISBN-13: 978-0-13-344710-1

Techniques for optimizing large-scale IP routing operation and managing network growth 

  • Understand the goals of scalable network design, including tradeoffs between network scaling, convergence speed, and resiliency
  • Learn basic techniques applicable to any network design, including hierarchy, addressing, summarization, and information hiding
  • Examine the deployment and operation of EIGRP, OSPF, and IS-IS protocols on large-scale networks
  • Understand when and how to use a BGP core in a large-scale network and how to use BGP to connect to external networks
  • Apply high availability and fast convergence to achieve 99.999 percent, or “five 9s” network uptime
  • Secure routing systems with the latest routing protocol security best practices
  • Understand the various techniques used for carrying routing information through a VPN

Optimal Routing Design provides the tools and techniques, learned through years of experience with network design and deployment, to build a large-scale or scalable IP-routed network. The book takes an easy-to-read approach that is accessible to novice network designers while presenting invaluable, hard-to-find insight that appeals to more advanced-level professionals as well.

Written by experts in the design and deployment of routing protocols, Optimal Routing Design leverages the authors’ extensive experience with thousands of customer cases and network designs. Boiling down years of experience into best practices for building scalable networks, this book presents valuable information on the most common problems network operators face when seeking to turn best effort IP networks into networks that can support Public Switched Telephone Network (PSTN)-type availability and reliability.

Beginning with an overview of design fundamentals, the authors discuss the tradeoffs between various competing points of network design, the concepts of hierarchical network design, redistribution, and addressing and summarization. This first part provides specific techniques, usable in all routing protocols, to work around real-world problems. The next part of the book details specific information on deploying each interior gateway protocol (IGP)—including EIGRP, OSPF, and IS-IS—in real-world network environments. Part III covers advanced topics in network design, including border gateway protocol (BGP), high-availability, routing protocol security, and virtual private networks (VPN). Appendixes cover the fundamentals of each routing protocol discussed in the book; include a checklist of questions and design goals that provides network engineers with a useful tool when evaluating a network design; and compare routing protocols strengths and weaknesses to help you decide when to choose one protocol over another or when to switch between protocols.

“The complexity associated with overlaying voice and video onto an IP network involves thinking through latency, jitter, availability, and recovery issues. This text offers keen insights into the fundamentals of network architecture for these converged environments.”

—John Cavanaugh, Distinguished Services Engineer, Cisco Systems®

This book is part of the Networking Technology Series from Cisco Press‚ which offers networking professionals valuable information for constructing efficient networks, understanding new technologies, and building successful careers.

Table of Contents




Part I                       Network Design Overview

Chapter 1               Network Design Goals and Techniques

Goals for Network Design


Packet Delivery Reliability

Packet Delivery Times

Delay and Jitter Budgets

The Impact of Network Design on Delay and Jitter Budgets

Reliability and Resiliency

Defining Network Failure

Network Recovery Time


Day-to-Day Operational Maintenance

Taking a Network Baseline

Network Documentation

Emergency Management



How Redundancy Increases Resiliency

Statistical Analysis

How Redundancy Can Increase Management Complexity

How Redundancy Can Reduce Scalability


Hiding Information

Hiding Topology Information

Hiding Reachability Information

Separate Functionality


Review Questions

Chapter 2          Applying the Fundamentals

Hierarchical Design

Abstraction Through Layering

Horizontal Layers in a Network

Layer Functions

Forwarding Traffic

Aggregation of Routing Information

Definition and Implementation of Routing Policies

User Attachment

Controlling Traffic Admittance into the Network

Network Hierarchies

Two-Layer Hierarchy

Three-Layer Hierarchy

Determining How Many Layers to Use in Network Design

Hiding Layers Within Layers

Creating Layers

Creating Choke Points

Separating Complexity from Complexity

Addressing and Summarization

Assigning Addresses in a Network

Working Around Addressing

Leaking More Specifics

Smaller Summary Blocks

Change the Logical Layout

Summary Issues

Summarization Black Holes

Summary Suboptimal Routing

Summary Metrics


Alternatives to IGP to IGP Redistribution

Single Point of Redistribution

Multiple Points of Redistribution



Review Questions

Part II           Interior Gateway Protocols

Chapter 3          EIGRP Network Design

Deploying EIGRP on a Large-Scale Three-Layer Hierarchical Network

Analyzing the Network Core for Summarization

Summarizing from the Core to the Distribution Layer

Summarizing into the Core at Its Edge

Analyzing the Network Distribution Layer for Summarization

Summarizing Toward the Network Core

Summarizing Toward the Remote Sites

Analyzing Routing in the Network Access Layer

Single-Homed Sites

Dual-Homed Remotes

Analyzing Use of the Stub Feature in Access Routers

Analyzing Routes to External Connections

Analyzing Routes to the Common Services Area

Analyzing Routes to Dial-In Clients

Host Routes

Bandwidth Issues

Deploying EIGRP on a Two-Layer Hierarchical Network

Summarization in the Core

Summarization in the Aggregation Layer

Summary of EIGRP Network Design

New Features in EIGRP

Third-Party Next Hop

NBMA Hub-and-Spoke Network

Redistributed Next Hop

Enhanced Route Map Support

Before Enhanced Route Map Support

Route Map Enhancements

Enhanced EIGRP Active Process

Case Study: Summarization Methods

IP Summary Addresses

Distribute Lists

Case Study: Controlling Query Propagation

Case Study: A Plethora of Topology Table Entries

Case Study: Troubleshooting EIGRP Neighbor Relationships

EIGRP Neighbor Relationships: Common Problem 1

EIGRP Neighbor Relationships: Common Problem 2

Case Study: Troubleshooting SIA Routes

Case Study: Redistribution

Using Distribute Lists to Prevent Redistribution Routing Loops

Using Route Maps to Prevent Redistribution Routing Loops

Using Prefix Lists to Prevent Redistribution Routing Loops

Setting the Administrative Distance to Troubleshoot Redistribution Routing Loops

Using External Flags to Prevent Redistribution Routing Loops

Case Study: Retransmissions and SIA

The Hold Timer

SIA Timer

Interaction Between the Hold Timer and the SIA Timer

Case Study: Multiple EIGRP Autonomous Systems

Review Questions

Chapter 4          OSPF Network Design

Summarization and Aggregation

Deploying OSPF on a Three-Layer Hierarchy

The Core Routers as ABRs

The Distribution Layer Routers as ABRs

Mixing ABR Locations

Deploying OSPF on a Two-Layer Hierarchy

Reducing Flooding Through Stub Areas

Stub Areas

Totally Stubby Areas

Not-So-Stubby Areas

Totally NSSA

Totally Stubby Not Really Full Areas

When to Use Stub Areas

Aggregating Routes in OSPF

Filtering Routes in OSPF

Deploying OSPF on Specific Topologies

Redistribution into OSPF

External Route Metrics

External Route Selection at ABRs

Route Selection Between Processes

Full Mesh Topologies

Hub-and-Spoke Topologies

Treating the NBMA Interface as a Broadcast Interface

Treating the NBMA Interface as a Set of Point-to-Point Interfaces

Treating an NBMA Interface as a Broadcast Point-to-Multipoint Interface

Treating an NBMA Interface as a Nonbroadcast Point-to-Multipoint Interface

Summary of Interface and OSPF Link-Type Options

Reducing Flooding to the Spokes

Links Parallel to Area Boundaries

Dial Links

Point-to-point Broadcast Links

Case Study: OSPF Externals and the Next Hop

Case Study: Troubleshooting OSPF Neighbor Adjacencies

Review Questions

Chapter 5          IS-IS Network Design

Deploying IS-IS on a Three-Layer Hierarchy

The Entire Network as a Single Routing Domain

The Core as the L2 Domain

Merging the Core and Distribution Layers into Level 2

Mixing and Overlapping the Level 1/Level 2 Border

Deploying IS-IS on a Two-Layer Hierarchy

Working with IS-IS Routing Areas

Leaking Routes into an L1 Routing Domain

Aggregating Routes in IS-IS

Deploying IS-IS on Specific Topologies


Full Mesh Topologies

Hub-and-Spoke Topologies

Point-to-Point Links

Broadcast Interfaces

Point-to-Point Broadcast Links

Links Parallel to Area Boundaries

Other Considerations in IS-IS Scaling


Excessive Link-State Flooding

LSP Corruption

Maximum Number of Pseudonodes

Prefix-Driven Routing Table Installation

Hello Padding Suppression

Case Study: Troubleshooting IS-IS Neighbor Relationships

Review Questions

Part II           Advanced Network Design

Chapter 6          BGP Cores and Network Scalability

Case Study: Troubleshooting BGP Neighbor Relationships

No IP Connectivity

eBGP Multihop

Other BGP Neighbor Problems

Logging Neighbor Changes

BGP in the Core

Case Study: Sample Migration

Scaling Beyond the Core

Dividing the Network into Pieces

Regional IGPs

BGP Network Growing Pains

BGP Update Generation Issues

Reducing the Number of Updates Generated

Case Study: Route Reflectors as Route Servers

External Connections

Case Study: Dual-Homed Connections to the Internet

Load Sharing on the Outbound Side

Load Sharing on the Inbound Side

Being a Transit AS

Case Study: Conditional Advertisement

Case Study: Route Dampening

Review Questions

Chapter 7          High Availability and Fast Convergence

Considerations in Fast Convergence

Network Meltdowns

Solving the Meltdown

Designing Routing Protocols Not to Melt

Do Not Report Everything You See

Non-Stop Forwarding

Graceful Restart

EIGRP Graceful Restart

OSPF Graceful Restart

IS-IS Graceful Restart

BGP Graceful Restart

Fast Down Detection

Detecting a Link or Adjacency Failure Using Polling

Bidirectional Forwarding Detection

Detecting a Link or Adjacency Failure Using Event-Driven Link Failure Notification


Frame Relay


Slowing Down When the Network Speeds Up

Link-State Exponential Backoff

Configuring OSPF Exponential Backoff for LSA Generation

Configuring OSPF Exponential Backoff for Running SPF

Configuring IS-IS Exponential Backoff

IP Event Dampening

Configuring IP Event Dampening

Calculating the Route Faster

EIGRP Feasible Successors

Link-State Partial SPF

Link-State Incremental SPF

Deploying GR and Fast Convergence Technologies

Graceful Restart Versus Fast Down Detection

How Fast Can GR Work?

Balancing Between GR and Fast Down Detection

Deploying Graceful Restart with BGP and an Interior Gateway
Protocol (IGP)

Deploying Exponential Backoff for Fast Convergence

Setting SPF Exponential Backoff Timers

Review Questions

Chapter 8          Routing Protocol Security

Fundamentals of Routing and Security

Understanding What a Routing System Is

Thoughts on Authorization and Authentication

Defining Authentication and Authorization

Transiting Authentication and Authorization

Transiting Authorization in a Routing System

Trust and Security

Determining the Reasons for an Attack on the Routing System

Types of Attacks Against Routing Systems

Disrupting Peering

Transport-Level Attacks Against OSPF and IS-IS

Transport-Level Attacks Against EIGRP

Transport-Level Attacks Against Border Gateway Protocol (BGP)

Protocol-Layer Attacks

Falsifying Routing Information

Disrupting Routing Domain Stability

Protecting Routing Domain Legitimacy

Protecting Routers from Being Compromised

Use Passwords

Filter Access to Routers

Protecting Against Illegitimate Devices Joining the Routing Domain

MD5 Authentication

Issues with MD5 Peer Authentication


Protecting Routers from Denial-of-Service Attacks

Edge Filters

The Generalized TTL Security Mechanism

Protecting Routing Information

Extranet Connections

Use an Exterior Gateway Protocol for All Extranet Connections

Filter Routes Aggressively at the Extranet Edge

Dampen Prefixes Aggressively at the Extranet Edge

Limiting Route Count at the Extranet Edge

Connections to the Internet

Route Filtering

Protecting Against Transit

Route Dampening

Future Directions in Routing Protocol Security

Protecting Against Illegitimate Devices Joining the Routing Domain

Secure Origin BGP (soBGP)

Begin at the Beginning: Who Are You?

The First Goal: Are You Authorized?

The Second Goal: Do You Really Have a Path?

Review Questions


Chapter 9          Virtual Private Networks


MPLS Basics

Overlay Routing over MPLS VPNs

Peer-to-Peer (Redistributed) Routing over MPLS VPNs







Case Study: NHRP in an ATM Network

Dynamic Multipoint IPSec VPNs

Review Questions


Part II               Appendixes

Appendix A           EIGRP for IP Basics of Operation

Appendix B            OSPF Basics of Operation

Appendix C            Integrated IS-IS Basics of Operation

Appendix D           Border Gateway Protocol 4 Basics of Operation

Appendix E            IP Network Design Checklist

Appendix F            Answers to Review Questions

Appendix G            Which Routing Protocol?


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