So what is the firewall using as the "outside" IP address? (I'm assuming you have control over the firewall, of course...). That should probably be the source IP you use.
__________________
L++ Se+++ GdY $++ Fr C+++ Csc Sf Ai AuO M+ MpTM S Ss RRSHP+ Pw- Fq->Fq+ Nd+++ Rp G++ Mm++ Bb---