I recently installed OpenSwan on my Fedora 13 machine. I want to use it to connect with Mac OS X with L2TP over IPSEC, unfortunately I am already stuck on the IPSEC-negotation part.

My server is running behind a NATted firewall so my external IP differs from the server's IP. The server has a fixed IP on the network and the same is almost always valid for the clients (they are usually behind a NATted firewall).

I installed OpenSwan on Fedora 13 and have following configuration:

config setup
    protostack=netkey
    nat_traversal=yes
    virtual_private=%v4:10.0.0.0/8,%v4:192.168.0.0/16,%v4:172.16.0.0/12
    oe=off
    nhelpers=0

conn L2TP-PSK-NAT
    rightsubnet=vhost:%priv
    also=L2TP-PSK-noNAT

conn L2TP-PSK-noNAT
    authby=secret
    pfs=no
    auto=add
    keyingtries=3
    rekey=no
    ikelifetime=8h
    keylife=1h
    type=transport
    left=my.servers.external.ip
    leftprotoport=17/1701
    right=%any
    rightprotoport=17/0

IPSEC starts fine and listens to UDP 500 and 4500. These two ports are opened in the firewall and are forwarded fine to the server.

In my /etc/ipsec.secrets file I have

my.servers.external.ip %any: "LongAndDifficultPassword"

And finally in my sysctl.conf (the redirect-entries are there because OpenSwan was strongly protesting about send/accept_redirects being active) I have

net.ipv4.ip_forward = 1
net.ipv4.conf.all.send_redirects = 0
net.ipv4.conf.all.accept_redirects = 0

Running "ipsec verify" gives me "all greens" (except Opportunistic Encryption Support, which is DISABLED), however, when trying to connect my Mac gives me following in the logs:

Nov  1 19:30:28 macbook pppd[4904]: pppd 2.4.2 (Apple version 412.3) started by user, uid 1011
Nov  1 19:30:28 macbook pppd[4904]: L2TP connecting to server 'my.servers.ip.address' (my.servers.ip.address)...
Nov  1 19:30:28 macbook pppd[4904]: IPSec connection started
Nov  1 19:30:28 macbook racoon[4905]: Connecting.
Nov  1 19:30:28 macbook racoon[4905]: IKE Packet: transmit success. (Initiator, Main-Mode message 1).
Nov  1 19:30:31 macbook racoon[4905]: IKE Packet: transmit success. (Phase1 Retransmit).
Nov  1 19:30:38: --- last message repeated 2 times ---
Nov  1 19:30:38 macbook pppd[4904]: IPSec connection failed

Any ideas at all?