IPSec forwarding

[Da Rock]

I'm having issues with pf firewall with a binat L2TP/IPSec VPN. From 
what I understand, no one can get IPSec to work through this firewall- 
it is unknown  what the actual problem is, but it looks like a rekeying 
problem: the connection is made but rekeying occurs immediately (alleged 
failure of phase 1/2?).

So I come to the folks here at IPFW with a general question: does IPSec 
have any known issues with IPFW? Including NAT? I've googled but haven't 
discovered any info on this. I would try testing this myself except for 
a severe lack of resources to attempt it, I would like some definitive 
proof that this works so I can try to narrow the problem down with pf 
(or change systems... :) ).

Cheers