Cisco ASA 5505 - Manual (Page 1525)

C H A P T E R
69-1
Cisco ASA 5500 Series Configuration Guide using the CLI
69
Configuring Remote Access IPsec VPNs
This chapter describes how to configure Remote Access IPsec VPNs and includes the following sections:
• Information About Remote Access IPsec VPNs, page 69-1
• Licensing Requirements for Remote Access IPsec VPNs, page 69-2
• Guidelines and Limitations, page 69-7
• Configuring Remote Access IPsec VPNs, page 69-7
• Configuration Examples for Remote Access IPsec VPNs, page 69-14
• Feature History for Remote Access VPNs, page 69-15
Information About Remote Access IPsec VPNs
Remote access VPNs allow users to connect to a central site through a secure connection over a TCP/IP
network such as the Internet. The Internet Security Association and Key Management Protocol, also
called IKE, is the negotiation protocol that lets the IPsec client on the remote PC and the ASA agree on
how to build an IPsec Security Association. Each ISAKMP negotiation is divided into two sections
called Phase1 and Phase2.
Phase 1 creates the first tunnel to protect later ISAKMP negotiation messages. Phase 2 creates the tunnel
that protects data travelling across the secure connection.
To set the terms of the ISAKMP negotiations, you create an ISAKMP policy. It includes the following:
• An authentication method, to ensure the identity of the peers.
• An encryption method, to protect the data and ensure privacy.
• A Hashed Message Authentication Codes (HMAC) method to ensure the identity of the sender and
to ensure that the message has not been modified in transit.
• A Diffie-Hellman group to set the size of the encryption key.
• A time limit for how long the ASA uses an encryption key before replacing it.
A transform set combines an encryption method and an authentication method. During the IPsec security
association negotiation with ISAKMP, the peers agree to use a particular transform set to protect a
particular data flow. The transform set must be the same for both peers.