These functions require an internet connection. Before processing the input
vector, we first check that a known hostname can be resolved. If this fails,
an error is raised.
If DNS lookup cannot resolve an input, then NA
is returned for that input.
If an error occurs during DNS lookup, then a warning is emitted and NA
is
returned for that input.
DNS resolution performs a many-to-many mapping between IP addresses and
hostnames. For this reason, there are two versions of each function. The
regular version returns just the first value and the _all()
suffix version
returns all values.