264Configuring IKEUnless otherwise specified, the term "IKE" in this chapter refers to IKEv1.OverviewBuilt on a framework defined by ISAKMP, Internet Key Exchange (IKE) provides automatic key negotiationand SA establishment services for IPsec, dramatically simplifying the configuration and maintenance ofIPsec.IKE is not intended solely for IPsec, but it is widely used for IPsec. This chapter describes how to use IKEfor IPsec.IKE provides the following benefits for IPsec:• Automatically negotiates IPsec parameters.• Performs DH exchanges to calculate shared keys, making sure each SA has a key independent ofother keys.• Automatically negotiates SAs when the sequence number in the AH or ESP header overflows,making sure IPsec can provide the anti-replay service by using the sequence number.As shown in Figure 82, IKE negotiates SAs for IPsec and transfers the SAs to IPsec, and IPsec uses the SAsto protect IP packets.Figure 82 Relationship between IKE and IPsecIKE negotiation processIKE negotiates keys and SAs for IPsec in two phases:1. Phase 1—The two peers establish an IKE SA, a secure, authenticated channel for communication.In this phase, two modes are available: main mode and aggressive mode.2. Phase 2—Using the IKE SA established in phase 1, the two peers negotiate to establish IPsec SAs.
