Multiple 360s - Open NATs, but cannot connect to each other

[sternn]

I've got a block of 5 IPs from my ISP.  I've got two Xbox 360s, each using one of those IPs on a 1:1 NAT with IP Aliases with UPnP disabled.  Whenever I do a connection test, they both come back as open NAT.  I can join the same game/party with both simultaneously if someone else is the host.  However, if one of mine is the host, the other cannot connect.  I've noticed this with GFWL games on my PCs as well.  I've looked around and tried various settings, but to no avail.  I'm just stumped.  Is a missing setting keeping these from talking to each other?

[sternn]

Fixed.  Turns out I didn't have NAT reflection turned on.  Once I turned that on, they could talk to each other.