<s>
The	O
Internet	O
Group	O
Management	O
Protocol	O
(	O
IGMP	O
)	O
is	O
a	O
communications	O
protocol	O
used	O
by	O
hosts	B-Device
and	O
adjacent	O
routers	B-Protocol
on	O
IPv4	B-Protocol
networks	I-Protocol
to	O
establish	O
multicast	O
group	O
memberships	O
.	O
</s>
<s>
IGMP	O
is	O
an	O
integral	O
part	O
of	O
IP	B-Protocol
multicast	I-Protocol
and	O
allows	O
the	O
network	O
to	O
direct	O
multicast	O
transmissions	O
only	O
to	O
hosts	B-Device
that	O
have	O
requested	O
them	O
.	O
</s>
<s>
IGMP	O
can	O
be	O
used	O
for	O
one-to-many	O
networking	O
applications	O
such	O
as	O
online	O
streaming	B-Application
video	I-Application
and	O
gaming	B-Application
,	O
and	O
allows	O
more	O
efficient	O
use	O
of	O
resources	O
when	O
supporting	O
these	O
types	O
of	O
applications	O
.	O
</s>
<s>
IGMP	O
is	O
used	O
on	O
IPv4	B-Protocol
networks	I-Protocol
.	O
</s>
<s>
Multicast	O
management	O
on	O
IPv6	B-Protocol
networks	O
is	O
handled	O
by	O
Multicast	B-Protocol
Listener	I-Protocol
Discovery	I-Protocol
(	O
MLD	O
)	O
which	O
is	O
a	O
part	O
of	O
ICMPv6	B-Protocol
in	O
contrast	O
to	O
IGMP	O
's	O
bare	O
IP	O
encapsulation	O
.	O
</s>
<s>
IGMP	O
operates	O
between	O
a	O
host	O
and	O
a	O
local	O
multicast	O
router	B-Protocol
.	O
</s>
<s>
Switches	B-Protocol
featuring	O
IGMP	B-Protocol
snooping	I-Protocol
also	O
derive	O
useful	O
information	O
by	O
observing	O
these	O
IGMP	O
transactions	O
.	O
</s>
<s>
Protocol	B-Protocol
Independent	I-Protocol
Multicast	I-Protocol
(	O
PIM	O
)	O
is	O
then	O
used	O
between	O
the	O
local	O
and	O
remote	O
multicast	O
routers	B-Protocol
to	O
direct	O
multicast	O
traffic	O
from	O
hosts	B-Device
sending	O
multicasts	O
to	O
hosts	B-Device
that	O
have	O
registered	O
through	O
IGMP	O
to	O
receive	O
them	O
.	O
</s>
<s>
IGMP	O
operates	O
on	O
the	O
network	B-Application
layer	I-Application
(	O
layer	B-Application
3	I-Application
)	O
,	O
just	O
the	O
same	O
as	O
other	O
network	O
management	O
protocols	O
like	O
ICMP	B-Protocol
.	O
</s>
<s>
The	O
IGMP	O
protocol	O
is	O
implemented	O
on	O
hosts	B-Device
and	O
within	O
routers	B-Protocol
.	O
</s>
<s>
A	O
host	B-Device
requests	I-Device
membership	O
to	O
a	O
group	O
through	O
its	O
local	O
router	B-Protocol
while	O
a	O
router	B-Protocol
listens	O
for	O
these	O
requests	O
and	O
periodically	O
sends	O
out	O
subscription	O
queries	O
.	O
</s>
<s>
A	O
single	O
router	B-Protocol
per	O
subnet	O
is	O
elected	O
to	O
perform	O
this	O
querying	O
function	O
.	O
</s>
<s>
Some	O
multilayer	B-Application
switches	I-Application
include	O
an	O
IGMP	O
querier	O
capability	O
to	O
allow	O
their	O
IGMP	B-Protocol
snooping	I-Protocol
features	O
to	O
work	O
in	O
the	O
absence	O
of	O
an	O
IGMP-capable	O
router	B-Protocol
in	O
the	O
layer	O
2	O
network	O
.	O
</s>
<s>
updates	O
both	O
IGMPv3	O
and	O
MLDv2	B-Protocol
to	O
better	O
support	O
source-specific	B-Protocol
multicast	I-Protocol
.	O
</s>
<s>
IGMPv3	O
improves	O
IGMPv2	O
by	O
supporting	O
source-specific	B-Protocol
multicast	I-Protocol
and	O
introduces	O
membership	O
report	O
aggregation	O
.	O
</s>
<s>
A	O
router	B-Protocol
supporting	O
IGMPv3	O
can	O
support	O
clients	O
running	O
IGMPv1	O
,	O
IGMPv2	O
and	O
IGMPv3	O
.	O
</s>
<s>
A	O
means	O
for	O
routers	B-Protocol
to	O
select	O
an	O
IGMP	O
querier	O
for	O
the	O
network	O
is	O
introduced	O
.	O
</s>
<s>
IGMPv3	O
introduces	O
source-specific	B-Protocol
multicast	I-Protocol
capability	O
.	O
</s>
<s>
Membership	O
reports	O
are	O
sent	O
to	O
224.0.0.22	B-Protocol
.	O
</s>
<s>
Sent	O
by	O
multicast	O
routers	B-Protocol
to	O
determine	O
which	O
multicast	O
addresses	O
are	O
of	O
interest	O
to	O
systems	O
attached	O
to	O
the	O
network(s )	O
they	O
serve	O
to	O
refresh	O
the	O
group	O
membership	O
state	O
for	O
all	O
systems	O
on	O
its	O
network	O
.	O
</s>
<s>
IGMP	O
messages	O
are	O
carried	O
in	O
bare	O
IP	O
packets	O
with	O
IP	B-Protocol
protocol	I-Protocol
number	I-Protocol
2	O
.	O
</s>
<s>
Similar	O
to	O
the	O
Internet	B-Protocol
Control	I-Protocol
Message	I-Protocol
Protocol	I-Protocol
,	O
there	O
is	O
no	O
transport	B-Architecture
layer	I-Architecture
used	O
with	O
IGMP	O
messaging	O
.	O
</s>
<s>
S	O
(	O
Suppress	O
Router-side	O
Processing	O
)	O
Flag	O
When	O
this	O
flag	O
is	O
set	O
,	O
it	O
indicates	O
to	O
receiving	O
routers	B-Protocol
that	O
they	O
are	O
to	O
suppress	O
the	O
normal	O
timer	O
updates	O
.	O
</s>
<s>
Routers	B-Protocol
should	O
update	O
their	O
Robustness	O
Variable	O
to	O
match	O
the	O
most	O
recently	O
received	O
query	O
unless	O
the	O
value	O
is	O
zero	O
.	O
</s>
<s>
The	O
FreeBSD	B-Operating_System
,	O
Linux	B-Application
and	O
Windows	B-Application
operating	I-Application
systems	I-Application
support	O
IGMP	O
at	O
the	O
host	O
side	O
.	O
</s>
