<s>
Source-specific	B-Protocol
multicast	I-Protocol
(	O
SSM	O
)	O
is	O
a	O
method	O
of	O
delivering	O
multicast	O
packets	O
in	O
which	O
the	O
only	O
packets	O
that	O
are	O
delivered	O
to	O
a	O
receiver	O
are	O
those	O
originating	O
from	O
a	O
specific	O
source	O
address	O
requested	O
by	O
the	O
receiver	O
.	O
</s>
<s>
SSM	O
requires	O
that	O
the	O
receiver	O
specify	O
the	O
source	O
address	O
and	O
explicitly	O
excludes	O
the	O
use	O
of	O
the	O
( *	O
,	O
G	O
)	O
join	O
for	O
all	O
multicast	O
groups	O
in	O
RFC	O
3376	O
,	O
which	O
is	O
possible	O
only	O
in	O
IPv4	B-Protocol
's	O
IGMPv3	B-Protocol
and	O
IPv6	B-Protocol
's	O
MLDv2	B-Protocol
.	O
</s>
<s>
Source-specific	B-Protocol
multicast	I-Protocol
is	O
best	O
understood	O
in	O
contrast	O
to	O
any-source	B-Protocol
multicast	I-Protocol
(	O
ASM	O
)	O
.	O
</s>
<s>
In	O
the	O
ASM	O
service	O
model	O
a	O
receiver	O
expresses	O
interest	O
in	O
traffic	O
to	O
a	O
multicast	B-Protocol
address	I-Protocol
.	O
</s>
<s>
In	O
the	O
SSM	O
service	O
model	O
,	O
in	O
addition	O
to	O
the	O
receiver	O
expressing	O
interest	O
in	O
traffic	O
to	O
a	O
multicast	B-Protocol
address	I-Protocol
,	O
the	O
receiver	O
expresses	O
interest	O
in	O
receiving	O
traffic	O
from	O
only	O
one	O
specific	O
source	O
sending	O
to	O
that	O
multicast	B-Protocol
address	I-Protocol
.	O
</s>
<s>
SSM	O
requires	O
support	O
in	O
last-hop	O
routers	O
and	O
in	O
the	O
receiver	O
's	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
Interest	O
in	O
multicast	O
traffic	O
from	O
a	O
specific	O
source	O
is	O
conveyed	O
from	O
hosts	O
to	O
routers	O
using	O
IGMPv3	B-Protocol
as	O
specified	O
in	O
RFC	O
4607	O
.	O
</s>
<s>
SSM	O
destination	O
addresses	O
must	O
be	O
in	O
the	O
ranges	O
232.0.0.0/8	O
for	O
IPv4	B-Protocol
.	O
</s>
<s>
For	O
IPv6	B-Protocol
current	O
allowed	O
SSM	O
destination	O
addresses	O
are	O
specified	O
by	O
ff3x::/96	O
,	O
where	O
the	O
hexadecimal	O
digit	O
x	O
represents	O
the	O
scope	O
.	O
</s>
