WordPress at a glance
filter is not described

pre_comment_user_ip filter-hook . WP 1.5.0

Filters the comment author's IP address before it is set.

Usage

add_filter( 'pre_comment_user_ip', 'filter_function_name_6820' );
function filter_function_name_6820( $comment_author_ip ){
	// filter...

	return $comment_author_ip;
}
$comment_author_ip(string)
The comment author's IP address.

Where the hook is called

wp_filter_comment()
wp-includes/comment.php 1859
$commentdata['comment_author_IP'] = apply_filters( 'pre_comment_user_ip', $commentdata['comment_author_IP'] );

Where the hook is used (in WP core)

Does not used.