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Configuring PIX Firewall IPSec Support

  • Sample Chapter is provided courtesy of Cisco Press.
  • Date: Feb 22, 2002.

Chapter Description

This chapter will teach you how to configure PIX Firewall IPSec using preshared keys for authentication and test and verify PIX Firewall IPSec.

Upon completing this chapter, you will be able to do the following:

  • Describe the tasks and steps used to configure IPSec support on the PIX Firewall

  • Describe the commands used to configure PIX Firewall IPSec encryption

  • Configure PIX Firewall IPSec using preshared keys for authentication

  • Test and verify PIX Firewall IPSec

This chapter shows you how to configure basic IP security (IPSec) in the PIX Firewall using preshared keys for authentication. It presents an overview of the tasks and steps you must perform to configure IPSec, provides details about IPSec-related commands in the PIX Firewall, and shows command examples. This chapter finishes with a case study based on the XYZ Company case study.

You will notice that the procedural tasks and steps outlined in this chapter are nearly identical to those used to configure preshared keys in Cisco IOS software, which is covered in Chapter 16, "Configuring Cisco IOS IPSec." The commands are very similar between the products as well because the source programming code for IPSec used in Cisco IOS software was ported over to the PIX Firewall.

A nice thing about the PIX Firewall commands is that all commands are entered in configuration mode; none of the PIX Firewall commands have submodes, which simplifies the configuration tasks and steps. Refer to Chapter 16 for more information on how IKE or IPSec works for preshared keys.

The intent of this chapter is to configure PIX Firewalls to become secure IPSec gateways that will encrypt and protect traffic flows of networks behind the PIX Firewalls, using preshared keys for authentication. The use of IKE preshared keys for authentication of IPSec sessions is relatively easy to configure yet does not scale well for a large number of IPSec clients. After you master this process, you will be able to configure Rivest, Shamir, and Adleman (RSA) signatures. This topic is covered in Chapter 18, "Scaling Cisco IPSec Networks."

Figure 17-1 shows the simplified topology for the XYZ Company used in examples in this chapter.

Figure 17-1 XYZ Company Topology for PIX Firewall IPSec

Four key tasks are involved in configuring IPSec encryption using preshared keys on the PIX Firewall:

  • Task 1: Prepare for IPSec—Preparing for IPSec involves determining the detailed encryption policy, including identifying the hosts and networks you want to protect, choosing an authentication method, determining details about the IPSec peers, identifying the IPSec features you need, and ensuring that existing access lists permit IPSec traffic.

  • Task 2: Configure Internet Key Exchange (IKE) for preshared keys—Configuring IKE involves enabling IKE, creating the IKE policies, and validating the configuration.

  • Task 3: Configure IPSec—IPSec configuration includes creating crypto access lists, defining transform sets, creating crypto map entries, and applying crypto map sets to interfaces.

  • Task 4: Test and verify the overall IPSec configuration—This task involves using show, debug, and related commands to test and verify that IPSec encryption works and to troubleshoot problems.

The following sections discuss each of these configuration tasks in more detail.

Task 1: Prepare for IPSec

Successfully implementing an IPSec network requires planning before you begin to configure individual PIX Firewalls and other IPSec peers. Configuring IPSec encryption can be complicated. You should begin by defining the detailed IPSec security policy based on the overall company security policy described in Appendix B, "An Example of an XYZ Company Network Security Policy." See Chapter 15, "Understanding Cisco IPSec Support," for more details on how to plan for IPSec. Here are some planning steps in preparing for IPSec:

Step 1

Determine the IKE (IKE Phase 1, or main mode) policy between IPSec peers based on the number and location of the peers.

Step 2

Determine the IPSec (IKE Phase 2, or quick mode) policy, including IPSec peer details such as IP addresses and IPSec transform sets and modes.

Step 3

Check the current configuration by using write terminal, show isakmp, show isakmp policy, show crypto map, and other show commands.

Step 4

Ensure that the network works without encryption to eliminate basic routing problems using the ping command and by running test traffic before encryption.

Step 5

Ensure that existing access lists in the perimeter router and PIX Firewall permit IPSec traffic, or the desired traffic will be filtered out.

2. Task 2: Configure IKE for Preshared Keys | Next Section

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