L2TP/IPSec NAT-T Update for Windows XP and Windows 2000
Microsoft has released an update package to enhance the current functionality of the Layer Two Tunneling Protocol (L2TP) and Internet Protocol security (IPSec) on computers that are running Windows XP or Windows 2000. This update includes improvements to IPSec to better support virtual private network (VPN) clients that are behind network address translation (NAT) devices. If you apply this update to a computer that is running Windows XP and if the IPSec service encounters a runtime error and cannot start for any reason, the IPSec driver operates in block mode because it cannot secure network traffic. (The IPSec service appears as "IPSEC services" in the list of system services.)