;;; If NAMESTR begins with a colon-terminated, defined, logical host,
;;; then return that host, otherwise return NIL.
(defun extract-logical-host-prefix (namestr start end)
;;; If NAMESTR begins with a colon-terminated, defined, logical host,
;;; then return that host, otherwise return NIL.
(defun extract-logical-host-prefix (namestr start end)