Unicast is a DNS routing scheme and is how most DNS networks work. An easy
way to think of Unicast networks is one-to-one. Unicast is taking an IP address
and assigning it to ONE unique nameserver. If you have the following
nameservers: ns1, ns2, ns3, each one of those nameservers will be responsible
for answering certain queries. If ns2 goes down due to power outage or severe
weather, the server will move on to the next available unicast server. If the
second server goes down due to being overloaded, your domain will be fully
inaccessible.