IPSec VPN Design

The definitive design and deployment guide for secure virtual private networks

• Learn about IPSec protocols and Cisco IOS IPSec packet processing
• Understand the differences between IPSec tunnel mode and transport mode
• Evaluate the IPSec features that improve VPN scalability and fault tolerance, such as dead peer detection and control plane keepalives
• Overcome the challenges of working with NAT and PMTUD
• Explore IPSec remote-access features, including extended authentication, mode-configuration, and digital certificates
• Examine the pros and cons of various IPSec connection models such as native IPSec, GRE, and remote access
• Apply fault tolerance methods to IPSec VPN designs
• Employ mechanisms to alleviate the configuration complexity of a large- scale IPSec VPN, including Tunnel End-Point Discovery (TED) and Dynamic Multipoint VPNs (DMVPN)
• Add services to IPSec VPNs, including voice and multicast
• Understand how network-based VPNs operate and how to integrate IPSec VPNs with MPLS VPNs

Among the many functions that networking technologies permit is the ability for organizations to easily and securely communicate with branch offices, mobile users, telecommuters, and business partners. Such connectivity is now vital to maintaining a competitive level of business productivity. Although several technologies exist that can enable interconnectivity among business sites, Internet-based virtual private networks (VPNs) have evolved as the most effective means to link corporate network resources to remote employees, offices, and mobile workers. VPNs provide productivity enhancements, efficient and convenient remote access to network resources, site-to-site connectivity, a high level of security, and tremendous cost savings.

IPSec VPN Design is the first book to present a detailed examination of the design aspects of IPSec protocols that enable secure VPN communication. Divided into three parts, the book provides a solid understanding of design and architectural issues of large-scale, secure VPN solutions. Part I includes a comprehensive introduction to the general architecture of IPSec, including its protocols and Cisco IOS® IPSec implementation details. Part II examines IPSec VPN design principles covering hub-and-spoke, full-mesh, and fault-tolerant designs. This part of the book also covers dynamic configuration models used to simplify IPSec VPN designs. Part III addresses design issues in adding services to an IPSec VPN such as voice and multicast. This part of the book also shows you how to effectively integrate IPSec VPNs with MPLS VPNs.

IPSec VPN Design provides you with the field-tested design and configuration advice to help you deploy an effective and secure VPN solution in any environment.

This security book is part of the Cisco Press® Networking Technology Series. Security titles from Cisco Press help networking professionals secure critical data and resources, prevent and mitigate network attacks, and build end-to-end self-defending networks.

Table of Contents

Introduction

Chapter 1      Introduction to VPNs   

Motivations for Deploying a VPN          

VPN Technologies      

Layer 2 VPNs         

Layer 3 VPNs         

Remote Access VPNs        

Summary        

Chapter 2      IPSec Overview  

Encryption Terminology           

Symmetric Algorithms   

Asymmetric Algorithms       

Digital Signatures    

IPSec Security Protocols         

IPSec Transport Mode   

IPSec Tunnel Mode

Encapsulating Security Header (ESP)          

Authentication Header (AH)  

Key Management and Security Associations     

The Diffie-Hellman Key Exchange    

Security Associations and IKE Operation     

IKE Phase 1 Operation   

IKE Phase 2 Operation   

IPSec Packet Processing   

Summary        

Chapter 3      Enhanced IPSec Features  

IKE Keepalives           

Dead Peer Detection   

Idle Timeout    

Reverse Route Injection    

RRI and HSRP   

Stateful Failover    

SADB Transfer   

SADB Synchronization 

IPSec and Fragmentation  

IPSec and PMTUD       

Look Ahead Fragmentation      

GRE and IPSec    

IPSec and NAT     

Effect of NAT on AH     

Effect of NAT on ESP   

Effect of NAT on IKE    

IPSec and NAT Solutions         

Summary 

Chapter 4      IPSec Authentication and Authorization Models   

Extended Authentication (XAUTH) and Mode Configuration (MODE-CFG)     

Mode-Configuration (MODECFG)   

Easy VPN (EzVPN)          

EzVPN Client Mode     

Network Extension Mode         

Digital Certificates for IPSec VPNs 

Digital Certificates        

Certificate Authority–Enrollment           

Certificate Revocation  

Summary 

Chapter 5      IPSec VPN Architectures  

IPSec VPN Connection Models     

 IPSec Model  

The GRE Model           

The Remote Access Client Model        

IPSec Connection Model Summary      

Hub-and-Spoke Architecture         

Using the IPSec Model

Transit Spoke-to-Spoke Connectivity Using IPSec         

Internet Connectivity

Scalability Using the IPSec Connection Model         

GRE Model

Transit Site-to-Site Connectivity     

Transit Site-to-Site Connectivity with Internet Access          

Scalability of GRE Hub-and-Spoke Models           

Remote Access Client Connection Model    

Easy VPN (EzVPN) Client Mode  

EzVPN Network Extension Mode 

Scalability of Client Connectivity Models      

Full-Mesh Architectures

Native IPSec Connectivity Model     

GRE Model

Summary        

Chapter 6      Designing Fault-Tolerant IPSec VPNs   

Link Fault Tolerance     

Backbone Network Fault Tolerance  

Access Link Fault Tolerance

Access Link Fault Tolerance Summary         

IPSec Peer Redundancy   

Simple Peer Redundancy Model     

Virtual IPSec Peer Redundancy Using HSRP           

IPSec Stateful Failover   

Peer Redundancy Using GRE         

Virtual IPSec Peer Redundancy Using SLB  

Server Load Balancing Concepts    

IPSec Peer Redundancy Using SLB     

Cisco VPN 3000 Clustering for Peer Redundancy     

Peer Redundancy Summary

Intra-Chassis IPSec VPN Services Redundancy

Stateless IPSec Redundancy          

Stateful IPSec Redundancy 

Summary        

Chapter 7      Auto-Configuration Architectures for Site-to-Site IPSec VPNs   

IPSec Tunnel Endpoint Discovery 

Principles of TED         

Limitations with TED     

TED Configuration and State     

TED Fault Tolerance     

Dynamic Multipoint VPN    

Multipoint GRE Interfaces         

Next Hop Resolution Protocol  

Dynamic IPSec Proxy Instantiation        

Establishing a Dynamic Multipoint VPN 

DMVPN Architectural Redundancy        

DMVPN Model Summary         

Summary 

Chapter 8      IPSec and Application Interoperability  

QoS-Enabled IPSec VPNs

Overview of IP QoS Mechanisms         

IPSec Implications for Classification      

IPSec Implications on QoS Policies      

VoIP Application Requirements for IPSec VPN Networks    

Delay Implications        

Jitter Implications         

Loss Implications         

IPSec VPN Architectural Considerations for VoIP   

Decoupled VoIP and Data Architectures

VoIP over IPSec Remote Access         

VoIP over IPSec-Protected GRE Architectures  

VoIP Hub-and-Spoke Architecture        

VoIP over DMVPN Architecture

VoIP Traffic Engineering Summary        

Multicast over IPSec VPNs      

Multicast over IPSec-protected GRE

Multicast on Full-Mesh Point-to-Point GRE/IPSec Tunnels     

DMVPN and Multicast          

Multicast Group Security      

Multicast Encryption Summary         

Summary        

Chapter 9      Network-Based IPSec VPNs  

Fundamentals of Network-Based VPNs 

The Network-Based IPSec Solution: IOS Features         

The Virtual Routing and Forwarding Table     

Crypto Keyrings      

ISAKMP Profiles     

Operation of Network-Based IPSec VPNs         

A Single IP Address on the PE       

Front-Door and Inside VRF  

Configuration and Packet Flow         

Termination of IPSec on a Unique IP Address Per VRF        

Network-Based VPN Deployment Scenarios     

IPSec to MPLS VPN over GRE       

IPSec to L2 VPNs   

PE-PE Encryption   

Summary        

Index   

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