[Openswan Users] VPN Client thru Alcatel Modem

[Leonard Tulipan]

Hi!

After a lot of debugging, I am finally stranded.
We have the followin setup

10.0.0.1 VPN Client
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Alcatel DSL Router Speedtouch 510
Changing IP's
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X.X.X.X Linux VPN Firewall
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192.168.118.* Private Net behind FW

Ok, nothing interesting.
Now, when I trace VPN Connections with tcpdump, I see

client:UDPPort500 -> server:Port500 ISAKMP Phase 1, 2, etc

So Packets ALWAYS come from Port 500 and go to Port 500
I also checked the VPN client it also behaves well and has Port 500 as 
src_port

But the Alcatel Router (after getting the firewall-config to let the 
corresponding traffic thru) changes all that, so that I get packets 
looking like
dslrouter:UDPPort(Random between 19000 and 20000) -> server:Port500

This does not work!
Is THIS the one reason I need the NAT-T Patch, or can I somehow get the 
server to accept packages, even though, the src_port isn't correct?

Cheers
Leonard