2.�Support in kernel (ESP and AH)

2.1.�Support in vanilla Linux kernel 2.4.x

At the time of writing missing in vanilla up to 2.4.28. There was an issue about keeping the Linux kernel source free of export/import-control-laws regarding encryption code. This is also one case why FreeS/WAN project wasn't included in vanilla source. Perhaps a backport from 2.6.x will be done in the future.

2.2.�Support in vanilla Linux kernel 2.6.x

Current versions (as time of writing 2.6.9 and upper) support native IPsec for IPv4 and IPv6.

Implementation was helped by the USAGI project.