Sprint maintains two sets of DNS servers. The first functions as Authoritative (non-recursive), and the second functions as Cache-Only (recursive). The Cache Only servers can be used by customer host machines to perform general DNS. You can put the IP addresses in the client machines on your network if you do not have your own Internet nameserver. I committed one of these three addresses to memory a decade ago (you never know when you might need it!). Google Public DNS server addresses are alot easier to memorize (18.104.22.168 and 22.214.171.124), but I like the stability of these Sprintlink servers.
NS1.SPRINTLINK.NET, 126.96.36.199, USA/Europe/Asia
NS2.SPRINTLINK.NET, 188.8.131.52, USA/Europe/Asia
NS3.SPRINTLINK.NET, 184.108.40.206, USA/Europe/Asia