In PgSQL 7.4.12,
foodb=# SELECT '255.255.255.255/24'::cidr;
ERROR: invalid cidr value: "255.255.255.255/24"
DETAIL: Value has bits set to right of mask.
foodb=#
SELECT '255.255.255.255/25'::cidr; cidr
--------------------255.255.255.255/25
(1 row)
foodb=#
in this case
11111111.11111111.11111111.11111111
has no bits set to right of 8 LSB ^
??
--
-Achilleus