I have a couple of centos5 hosts at various offices connected with ipsec by ipsec-tools (racoon). It's a relatively straightforward configuration on ipv4, however I can't find any information how and even if it works in the same way with ipv6.
What I've found is some references that it is better to use openswan on el5 and it indeed is standard on el6. It promises ipv6 support by default, however, I couldn't get it to even do phase 1 on el5 in the limited time I had available to test it. I've also found out that openswan is poorly documented not only on their site, but also in el6 manuals.
So ... what are the general expiriences with ipsec on ipv6? Anyone has it running? What software did you use?