Thanks.  That was definitely part of the problem. I've added the following to my iptables to fix the IP Masq problem and now I can see the packets coming in correctly in tcpdump but now I seem to be having a routing problem.  Could still be an iptables issue.  I'll post if I can figure it out.

iptables -t nat -I PREROUTING 1 -p 50 -j ACCEPT
iptables -t nat -I POSTROUTING 1 -p 50 -j ACCEPT

mjk <> wrote:
I think It has something to do with "IP Masquarade".
Try to disable "IP masquarade".

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