Hello,

I have 1 domain on one server but need to use subdomains over 2 servers like:

server 1
ns3.domain.com
ns4.domain.com

server 2
ns5.domain.com
ns6.domain.com

How can i do it?

Go to your domain registrar and set up subdomains with the ip addresses of the specific servers.

I think you could just out it all across like private nameservers. Just put the IP for 3 and 4 on server 2’s IP and redirect it to a subdomain.

Yes, I think this setting is going to be under your domain registrar. Check it out with them if you can make several sub domains under your main domain account. Else, you may need to simply share the servers used by your main domain.