I had quite trouble with this so i want to share and save time you and me when needing this.

If you are not expert, here is how to do it. How to register 2 sets of domain nameservers, point them to hosting.

So first you have a domain name registered somewhere.

1. What i would do first is looking into your domain registar control panel and looking up your domain name, enter it and look for Register nameservers, or nameservers or DNS hyperlinks.

2. register your nameservers like:
ns1.mydomain.com myhosting1firstIPhere
ns2.mydomain.com myhosting1secondIPhere
ns3.mydomain.com myhosting2firstIPhere
ns4.mydomain.com myhosting2secondIPhere

so for example when you have hosting company at mydomain.com and you have 2 different servers or two different reseller accounts with 2 companies. you can register ns1 and ns2 for one company and ns3 and ns4 for other. You always need to have 2 nameservers avaialble for your custommers domain names. Custommers then just enter your 2 namesers into their domain registar control panels. If you have only one IP you can also do as a second IP. This is not ideal solution and make your second nameserver not responding.

3. after you register nameservers with your hosting account/server IPs, you should modiffy your hosting account nameserver setting. Meaning instruct your hosting server to accept these connections. How to do it? Find DNS section or "Edit Zone" section in your hosting account. Select zone for proper domain name "mydomain.com" and then add this:

ns1 14400 in A yourhostingnameserverIPaddress
ns2 14400 in A yourhostingnameserverIPaddress
ns3 14400 in A yourhostingnameserverIPaddress
ns4 14400 in A yourhostingnameserverIPaddress

So there are always 5 fields you need to set. (nameserver name, 14400, in, A as a zone)

4. After this is done, im not sure if its necessary to restart network daemon or named on server (service named restart, service network restart), but you should be DONE and within some minutes, hours, you should be able to see your domain nameservers and its IPs when you lookup your nameserver at http://www.who.is/nameserver/ns3.mydomain.com/ You may try also http://network-tools.com, (select Non-cached DNS)

If you have anything to say to improve this guide, please share. Thank You