HUUUUUURRRRAAAAAAA... I GET IT
Finally, after a lot of testing, I get it.
I changed all my network, I set the nanostation as a router (before was a bridge) and that way, the DNS status has changed to OK, remoterig.com=193.202.xxx.xxx
Now is working either with fix IP or with DHCP (doesn't matter).
I hope tomorrow, when I'll get home, not to have problems with DMZ configuration.
Thanks Mitch, 73's