From the NannyMUD documentation

LAST CHANGE

2000-12-19

FUNCTION

NAME
        query_ip_name - Get the host name for an object.


SYNTAX
  string query_ip_name(mixed arg)

DESCRIPTION
  This sfun will give you a string with the result of a DNS lookup
  for the argument. Valid arguments might be a string, an object
  or nothing at all. In the latter case previous_object() is used.