SELECT * FROM t1;
       ip
----------------
  192 . 168 . 0 . 0 / 16 
  192 . 168 . 1 . 0 / 24 
( 2  rows)

SELECT * FROM t2;
     ip
-------------
  192 . 168 . 1 . 1 
( 1  row)

 EXPLAIN SELECT t1.ip FROM t2 LEFT OUTER JOIN t1 ON (t1.ip>>=t2.ip AND masklen(t1.ip)=(SELECT max(masklen(t1.ip)) FROM t1 WHERE t1.ip>>=t2.ip));
                                   QUERY PLAN
--------------------------------------------------------------------------------
 Merge Left Join  (cost= 181 . 86 .. 277555 . 26  rows= 4290  width= 64 )
   Merge Cond: (((subplan)) = (masklen(public.t1.ip)))
   Join Filter: (public.t1.ip >>= t2.ip)
   ->  Sort  (cost= 90 . 93 .. 94 . 20  rows= 1310  width= 32 )
         Sort Key: ((subplan))
         ->  Seq Scan on t2  (cost= 0 . 00 .. 23 . 10  rows= 1310  width= 32 )
               SubPlan
                 ->  Aggregate  (cost= 28 . 02 .. 28 . 03  rows= 1  width= 32 )
                       ->  Seq Scan on t1  (cost= 0 . 00 .. 26 . 38  rows= 655  width= 32 )
                             Filter: (ip >>= $ 0 )
   ->  Sort  (cost= 90 . 93 .. 94 . 20  rows= 1310  width= 32 )
         Sort Key: (masklen(public.t1.ip))
         ->  Seq Scan on t1  (cost= 0 . 00 .. 23 . 10  rows= 1310  width= 32 )
( 13  rows)