Aliases are useful in allowing service names eg www, ftp, smtp
etc to map onto a single host. This works through using a CNAME for
the alias name which points back to the canonical name of the host.
Disadvantages are:
Performance hit through the additional indirection
Adminstrative problems, since there is no backwards pointer
from the canonical host name entry to the aliases. Can be made
easier by decent tools.
Using the alias name where a reverse or PTR lookup is required
ensures that the names don't correspond
IP addresses have their own portion of the dns tree under
inaddr.arpa. This space is managed by ARIN, who keep the netnumbers
on the root servers, which have entries for all net numbers. Each
net number has an NS entry to point to the particular dns server
which maintains the tables for the individual hosts.
