[the_common_man]

$ host -t NS digitalocean.com

digitalocean.com name server walt.ns.cloudflare.com.

digitalocean.com name server kim.ns.cloudflare.com.

[cancancan]

That may not necessarily work. Example:

  $ host -t NS okcupid.com
  okcupid.com name server nameserver2.okcupid.com.
  okcupid.com name server nameserver1.okcupid.com.

But if you check the response headers you'll see 'CF-RAY:...' and 'Server: cloudflare-nginx'