The length of the IP Netmask for Reachability Address.
The values for the index objects isisIPRADest and
isisIPRADestPrefixLen must be consistent. When the value
of isisIPRADest (excluding the zone index, if one
is present) is x, then the bitwise logical-AND
of x with the value of the mask formed from the
corresponding index object isisIPRADestPrefixLen MUST be
equal to x. If not, then the index pair is not
consistent, and an inconsistentName error must be
returned on SET or CREATE requests.