Hello ! I buy SEO shared hosting on this website : http://www.cclassiphosting.com/ to have many differents IP adress. I tried to have custom DNS like ns1.domain.com and ns2.domain.com for each domain but that dont work. I did all the support say me and they stop to help me 2 days ago. It's first time i have problem with DNS because usually i use default DNS provide by the Hoster. If someone know how to create custom DNS with cclassiphosting.com or know better (more easy) hoster with many differents IP (Class C), i will be happy
Well, if they won't help you? Get another host company! Or you just can not understand what they told you.
To create name servers for a domain you need to point sub-domains ot child name servers to the IP address/s of your server. This means that ns1.yourdomain.com could have an 'A record' to your ip and this would then work as an name server. Previous poster is right, your hosting provider should help with such questions.