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Configuring PIX firewall IPsec support

A look at the steps involved in configuring Cisco's PIX firewall.

With a competitively priced firewall product and the prevalence of Cisco routers, one would think PIX would be the most popular firewall device. Some complain that PIX is difficult to configure. In the following tip excerpted form InformIT, writer Mike Wenstrom takes a look at the necessary tasks involved in configuring PIX firewall IPSec support.

Mike Wenstrom is the author of Managing Cisco Network Security.

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:

  1. Determine the IKE (IKE Phase 1, or main mode) policy between IPsec peers based on the number and location of the peers.
  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.
  3. Check the current configuration by using write terminal, show isakmp, show isakmp policy, show crypto map, and other show commands.
  4. Ensure that the network works without encryption to eliminate basic routing problems using the ping command and by running test traffic before encryption.
  5. Ensure that existing access lists in the perimeter router and PIX Firewall permit IPsec traffic, or the desired traffic will be filtered out.

Task 2: Configure IKE for Preshared Keys

The next major task in configuring PIX Firewall IPsec is to configure IKE parameters gathered earlier. Note that, in PIX configuration commands, ISAKMP is synonymous with IKE. Configuring IKE consists of the following essential steps and commands, which are covered in subsequent sections in more detail:

  1. Enable or disable IKE with the isakmp enable command.
  2. Create IKE policies with the isakmp policy commands.
  3. Configure preshared keys with the isakmp key and associated commands.
  4. Verify the IKE configuration with the show isakmp [policy] command.

Task 3: Configure IPSec

The next major task in configuring PIX Firewall IPsec is to configure the IPsec parameters previously gathered. This section presents the steps used to configure IPsec. The general tasks and commands used to configure IPsec encryption on PIX Firewalls are summarized as follows. Subsequent sections discuss each configuration step in detail.

  1. Configure crypto access lists with the access-list command.
  2. Configure transform set suites with the crypto ipsec transform-set command.
  3. (Optional) Configure global IPsec security association lifetimes with the crypto ipsec security-association lifetime command.
  4. Configure crypto maps with the crypto map command.
  5. Apply crypto maps to the terminating/originating interface with the crypto map map-name interface interface command.
  6. Verify IPsec configuration with the variety of available show commands.

Task 4: Test and Verify the Overall IPsec Configuration

The final step in configuring IPsec for preshared keys is to verify that all the IKE and IPsec values were configured correctly and to test it to ensure that it works properly. The PIX Firewall contains a number of show, clear, and debug commands that are useful for testing and verifying IKE and IPsec, which are summarized in this section.

For a much more detailed description of these tasks, click over to InformIT. Registration is required, but it's free.

This was last published in April 2002

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