A host has registered nameservers as ns1.thedomain.com and ns2.thedomain.com. Two more nameservers are required for a separate hosting account. Is it sensible to register these as ns3.thedomain.com and ns4.thedomain.com or is it wiser to have ns1.newdomain.com and ns2.newdomain.com with a different Registrar?

thanks,

Tom

If it's something that you need, it'll be find to register both sets of nameservers using the same domain. You won't have any problems doing that.