If you do not have the time to read that excellent book Implementing IPsec, Making Security Work on VPNs, Intranets and Extranets (Kaufman, E. and Newman, A., Wiley, 1999), perhaps you do have time to fine hone your learning curve and access a more potted version at http://csrc.nist.gov/ipsec. Firstly, let us remind ourselves about the security services that Ipsec provides: data origin authentication, connectionless integrity, replay protection, data confidentiality, limited traffic flow confidentiality and key negotiation and management.