see also: Networking in linux, IPSec, 26sec, Openswan

• get linux 2.6 source
• apply KLIPS26 patch from www.openswan.org
• apply NAT-T (KLIPS) patch from www.openswan.org

configuration: When going through the options, the following changes needs to be made. All are in the networking options.

1. The PF KEY sockets option should be either modular or unset.
2. The IPSEC NAT-Traversal (KLIPS compatible) option should be compiled in the kernel.
3. The Openswan IPsec (KLIPS26) option should be compiled in the kernel. Then enter the KLIPS options and enable every option apart from the CryptoAPI algorithm interface option.

for all the compiling erros see troubleshooting.

 net/ipsec/aes/ipsec_alg_aes.c:82: error: syntax error before string constant

See: BUG

Apply this patch: http://bugs.xelerance.com/view.php?id=636, this shoud be fixed in 2.4.6 Openswan.