I use no-ip for as registar and I got this reply :
You must have the hosts defined in DNS. Since you have the Basic service for xxx.com you won't be able to create ns1. and ns2.xxx.com with different IP addresses.
That means I have to pay for their plus package to just setup the ns1&ns2 ? Every register doesn't offer that for free ? There was an option to specify two name servers and two ip addreses.