<s>
6over4	B-Protocol
is	O
an	O
IPv6	B-Protocol
transition	O
mechanism	O
meant	O
to	O
transmit	O
IPv6	B-Protocol
packets	B-Protocol
between	O
dual-stack	O
nodes	O
on	O
top	O
of	O
a	O
multicast-enabled	O
IPv4	B-Protocol
network	I-Protocol
.	O
</s>
<s>
IPv4	B-Protocol
is	O
used	O
as	O
a	O
virtual	O
data	B-Protocol
link	I-Protocol
layer	I-Protocol
(	O
virtual	O
Ethernet	O
)	O
on	O
which	O
IPv6	B-Protocol
can	O
be	O
run	O
.	O
</s>
<s>
6over4	B-Protocol
defines	O
a	O
trivial	O
method	O
for	O
generating	O
a	O
link-local	O
IPv6	B-Protocol
address	O
from	O
an	O
IPv4	B-Protocol
address	O
,	O
and	O
a	O
mechanism	O
to	O
perform	O
Neighbor	B-Protocol
Discovery	I-Protocol
on	O
top	O
of	O
IPv4	B-Protocol
.	O
</s>
<s>
Any	O
host	O
wishing	O
to	O
participate	O
in	O
6over4	B-Protocol
over	O
a	O
given	O
IPv4	B-Protocol
network	I-Protocol
can	O
set	O
up	O
a	O
virtual	O
IPv6	B-Protocol
network	O
interface	O
.	O
</s>
<s>
the	O
lower-order	O
32	O
bits	O
to	O
the	O
binary	O
value	O
must	O
be	O
that	O
of	O
the	O
IPv4	B-Protocol
address	O
of	O
the	O
host	O
.	O
</s>
<s>
For	O
example	O
,	O
host	O
192.0.2.142	O
would	O
use	O
fe80:0000:0000:0000:0000:0000:c000:028e	O
as	O
its	O
link-local	O
IPv6	B-Protocol
address	O
(	O
192.0.2.142	O
is	O
c000028e	O
in	O
hexadecimal	O
notation	O
)	O
.	O
</s>
<s>
To	O
perform	O
ICMPv6	B-Protocol
Neighbor	B-Protocol
Discovery	I-Protocol
,	O
multicast	O
must	O
be	O
used	O
.	O
</s>
<s>
Any	O
IPv6	B-Protocol
multicast	O
packet	B-Protocol
gets	O
encapsulated	O
in	O
an	O
IPv4	B-Protocol
multicast	O
packet	B-Protocol
with	O
destination	O
239.192.x.y	O
,	O
where	O
x	O
and	O
y	O
are	O
the	O
penultimate	O
and	O
last	O
bytes	O
of	O
the	O
IPv6	B-Protocol
multicast	O
address	O
respectively	O
.	O
</s>
<s>
Given	O
a	O
link-local	O
address	O
and	O
a	O
multicast	O
addresses	O
mapping	O
,	O
a	O
host	O
can	O
use	O
ICMPv6	B-Protocol
to	O
discover	O
its	O
on-link	O
neighbors	O
and	O
routers	O
,	O
and	O
usually	O
perform	O
stateless	O
autoconfiguration	O
,	O
as	O
it	O
would	O
do	O
on	O
top	O
of	O
,	O
e.g.	O
</s>
<s>
6over4	B-Protocol
relies	O
on	O
IPv4	B-Protocol
multicast	O
availability	O
which	O
is	O
not	O
very	O
widely	O
supported	O
by	O
IPv4	B-Protocol
networking	O
infrastructure	O
.	O
</s>
<s>
6over4	B-Protocol
is	O
of	O
limited	O
practical	O
use	O
,	O
and	O
is	O
not	O
supported	O
by	O
the	O
most	O
common	O
operating	B-General_Concept
systems	I-General_Concept
.	O
</s>
<s>
To	O
connect	O
IPv6	B-Protocol
hosts	O
on	O
different	O
physical	O
links	O
,	O
IPv4	B-Protocol
multicast	O
routing	O
must	O
be	O
enabled	O
on	O
the	O
routers	O
connecting	O
the	O
links	O
.	O
</s>
<s>
ISATAP	B-Protocol
is	O
a	O
more	O
complex	O
alternative	O
to	O
6over4	B-Protocol
which	O
does	O
not	O
rely	O
on	O
IPv4	B-Protocol
multicast	O
.	O
</s>
