VPN BasicsBasic VPN MethodologyWhat Is Tunneling?Packet-Level View of TunnelingAdvantages and Disadvantages of VPNsBenefits of a VPNSecurityDeployment AdvantagesCost EffectivenessDisadvantages of VPNProcessing OverheadPacket OverheadImplementation IssuesTroubleshooting and Control IssuesInternet Availability IssuesIPSec BasicsIPSec Protocol SuiteSAIPSec Tunnel and Transport ModesIKEIKE Phase 1Annotated IKE Phase 1 ExampleIKE Phase 2Annotated IKE Phase 2 ExampleIPSec Security Protocols AH and ESPAH ProtocolESPCombined Use of ESP and AHIPSec Configuration ExamplesCisco Router VPN ExamplesWindows XP IPSec Configuration ExampleOther VPN Protocols: PPTP and L2TPPPTPL2TPComparison of PPTP, L2TP, and IPSecPPTP and L2TP ExamplesClient Windows XP SetupCisco PIX VPDN Setup for PPTP TrafficSummaryReferences