mysql> CREATE TABLE _netbounds_test
    -> (
    ->   id INTEGER UNSIGNED NOT NULL,
    ->   netpoly GEOMETRY NOT NULL,
    ->   ip_from INTEGER UNSIGNED NOT NULL,
    ->   ip_to   INTEGER UNSIGNED NOT NULL,
    ->   PRIMARY KEY (id),
    ->   SPATIAL INDEX i_net (netpoly)
    -> );
Query OK, 0 rows affected (0.15 sec)

mysql> INSERT INTO _netbounds_test ( id, netpoly, ip_from, ip_to )
    -> SELECT id, GEOMFROMWKB(POLYGON(LINESTRING(
    ->   POINT(net, -1),
    ->   POINT(net + POWER(2,32-cidr)-1, -1),
    ->   POINT(net + POWER(2,32-cidr)-1,  1),
    ->   POINT(net,  1),
    ->   POINT(net, -1)
    -> ))),
    ->   net, net + POWER(2,32-cidr)-1
    -> FROM networks
    -> WHERE cidr != 0;
Query OK, 119663 rows affected (32.89 sec)
Records: 119663  Duplicates: 0  Warnings: 0



(1a)
mysql> EXPLAIN
    -> SELECT id, INET_NTOA(n.net) net, cidr, ASTEXT(netpoly) geom
    -> FROM _netbounds_test t FORCE INDEX (i_net)
    -> LEFT JOIN networks n USING (id)
    -> WHERE Contains( t.netpoly, GEOMFROMWKB( POINT( INET_ATON('10.1.68.47'), 0 ) ) ) =1;
+----+-------------+-------+--------+---------------+---------+---------+----------------+--------+-------------+
| id | select_type | table | type   | possible_keys | key     | key_len | ref            | rows   | Extra       |
+----+-------------+-------+--------+---------------+---------+---------+----------------+--------+-------------+
|  1 | SIMPLE      | t     | ALL    | NULL          | NULL    | NULL    | NULL           | 119663 | Using where | 
|  1 | SIMPLE      | n     | eq_ref | PRIMARY       | PRIMARY | 4       | inventory.t.id |      1 |             | 
+----+-------------+-------+--------+---------------+---------+---------+----------------+--------+-------------+
2 rows in set (0.01 sec)

(1b)
mysql> SELECT id, INET_NTOA(n.net) net, cidr, ASTEXT(netpoly) geom
    -> FROM _netbounds_test t FORCE INDEX (i_net)
    -> LEFT JOIN networks n USING (id)
    -> WHERE Contains( t.netpoly, GEOMFROMWKB( POINT( INET_ATON('10.1.68.47'), 0 ) ) ) =1;
+----+-----------+------+---------------------------------------------------------------------------+
| id | net       | cidr | geom                                                                      |
+----+-----------+------+---------------------------------------------------------------------------+
| 15 | 10.0.0.0  |   10 | POLYGON((167772160 -1,171966463 -1,171966463 1,167772160 1,167772160 -1)) | 
| 39 | 10.1.68.0 |   23 | POLYGON((167855104 -1,167855615 -1,167855615 1,167855104 1,167855104 -1)) | 
+----+-----------+------+---------------------------------------------------------------------------+
2 rows in set (1.46 sec)



(2a)
mysql> EXPLAIN
    -> SELECT id, INET_NTOA(n.net) net, cidr, ASTEXT(netpoly) geom
    -> FROM _netbounds_test t FORCE INDEX (i_net)
    -> LEFT JOIN networks n USING (id)
    -> WHERE Contains( t.netpoly, GEOMFROMWKB( POINT( INET_ATON('10.1.68.47'), 0 ) ) );
+----+-------------+-------+--------+---------------+---------+---------+----------------+------+-------------+
| id | select_type | table | type   | possible_keys | key     | key_len | ref            | rows | Extra       |
+----+-------------+-------+--------+---------------+---------+---------+----------------+------+-------------+
|  1 | SIMPLE      | t     | range  | i_net         | i_net   | 32      | NULL           |    1 | Using where | 
|  1 | SIMPLE      | n     | eq_ref | PRIMARY       | PRIMARY | 4       | inventory.t.id |    1 |             | 
+----+-------------+-------+--------+---------------+---------+---------+----------------+------+-------------+
2 rows in set (0.00 sec)

(2b)mysql> SELECT id, INET_NTOA(n.net) net, cidr, ASTEXT(netpoly) geom
    -> FROM _netbounds_test t FORCE INDEX (i_net)
    -> LEFT JOIN networks n USING (id)
    -> WHERE Contains( t.netpoly, GEOMFROMWKB( POINT( INET_ATON('10.1.68.47'), 0 ) ) );
Empty set (0.00 sec)