Difference between REMOTE_HOST and REMOTE_ADDR

Question

What is the difference between these two variables?

REMOTE_HOST and REMOTE_ADDR.

Answer 1

REMOTE_HOST pertains to the hostname of the client (i.e. the computer making the request). REMOTE_ADDR refers to the IP address of the client.

There would be times when the hostname is unresolvable so the REMOTE_HOST will return the REMOTE_ADDR or the IP address instead.