port 53 tcp/udp
communication can be tested by telnetting to port 53

host.subdomain.second-level domain.top-level domain.
entire name cannot exceed 255 characters
each subname cannot exceed 63 characters
allowed chracters: A-Z, a-z, 0-9, and "-"

example of reverse lookup zone: 1.168.192.in-addr.arpa (class c)
class a = one octet, class b = two octets

location of dns zone files:

types of records:
A records = hosts

round-robin DNS is achieved by having the same hostname for several different IP addresses.