Contents
Foreword
Introduction
Part I Network Design Overview
Chapter 1 Network Design Goals and Techniques
Goals for Network Design
Reliability
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
Manageability
Day-to-Day Operational Maintenance
Taking a Network Baseline
Network Documentation
Emergency Management
Scalability
Redundancy
How Redundancy Increases Resiliency
Statistical Analysis
How Redundancy Can Increase Management Complexity
How Redundancy Can Reduce Scalability
Layering
Hiding Information
Hiding Topology Information
Hiding Reachability Information
Separate Functionality
Summary
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
Redistribution
Alternatives to IGP to IGP Redistribution
Single Point of Redistribution
Multiple Points of Redistribution
Filters
Tags
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
Redistribution
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
Metrics
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
SONET
Frame Relay
Ethernet
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
IPSec
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
References
Chapter 9 Virtual Private Networks
MPLS
MPLS Basics
Overlay Routing over MPLS VPNs
Peer-to-Peer (Redistributed) Routing over MPLS VPNs
BGP/MPLS VPNs
EIGRP
OSPF
IPSec
GRE
NHRP
Case Study: NHRP in an ATM Network
Dynamic Multipoint IPSec VPNs
Review Questions
References
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?
Index
