HP ProCurve 6200yl Multicast And Routing Manual page 131

group-prefix < group-addr/mask >: Specifies the multicast
group(s) to advertise as supported by the RP candidate. Use
this option when you want to enable the Candidate-RP and
simultaneously configure it to support a subset of multicast
addresses or ranges of addresses instead of all possible
multicast addresses.
A group prefix can specify all multicast groups (224.0.0.0 -
239.255.255.255), a range (subset) of groups, or a single
group. A given address is defined by its nonzero octets and
mask. The mask is applied from the high end (leftmost) bits
of the address and must extend to the last nonzero bit in the
lowest-order, nonzero octet. Any intervening zero or nonzero
octet requires eight mask bits. For example:
228.0.0.64/26: Defines a multicast address range of 228.0.0.64
through 228.0.0.127. (The last six bits of the rightmost octet
are wildcards.)
228.0.0.64/30: Defines a multicast address range of 228.0.0.64
through 228.0.0.67. (The last two bits of the rightmost octet
are wildcards.)
228.0.0.64/32: Defines a single multicast address of 228.0.0.64.
(There are no wildcards in this group prefix.)
228.0.0.64/25: Creates an error condition due to the mask failing
to include the last (rightmost) nonzero bit in the lowest-order,
nonzero octet. (That is, this mask supports an address of
228.0.0.128, but not 228.0.0.64.)
Note that the larger the mask, the smaller the range of
multicast addresses supported. A mask of 32 bits always
specifies a single multicast address. For example:
230.0.15.240/32: Defines a single multicast address of
230.0.15.240.
PIM-SM (Sparse Mode)
Configuring PIM-SM on the Router
4-39