<s>
Internet	B-Protocol
Control	I-Protocol
Message	I-Protocol
Protocol	I-Protocol
version	I-Protocol
6	I-Protocol
(	O
ICMPv6	B-Protocol
)	O
is	O
the	O
implementation	O
of	O
the	O
Internet	B-Protocol
Control	I-Protocol
Message	I-Protocol
Protocol	I-Protocol
(	O
ICMP	B-Protocol
)	O
for	O
Internet	B-Protocol
Protocol	I-Protocol
version	I-Protocol
6	I-Protocol
(	O
IPv6	B-Protocol
)	O
.	O
</s>
<s>
ICMPv6	B-Protocol
is	O
an	O
integral	O
part	O
of	O
IPv6	B-Protocol
and	O
performs	O
error	O
reporting	O
and	O
diagnostic	O
functions	O
.	O
</s>
<s>
ICMPv6	B-Protocol
has	O
a	O
framework	O
for	O
extensions	O
to	O
implement	O
new	O
features	O
.	O
</s>
<s>
Several	O
extensions	O
have	O
been	O
published	O
,	O
defining	O
new	O
ICMPv6	B-Protocol
message	O
types	O
as	O
well	O
as	O
new	O
options	O
for	O
existing	O
ICMPv6	B-Protocol
message	O
types	O
.	O
</s>
<s>
For	O
example	O
,	O
Neighbor	B-Protocol
Discovery	I-Protocol
Protocol	I-Protocol
(	O
NDP	B-Protocol
)	O
is	O
a	O
node	O
discovery	O
protocol	O
based	O
on	O
ICMPv6	B-Protocol
which	O
replaces	O
and	O
enhances	O
functions	O
of	O
ARP	O
.	O
</s>
<s>
Secure	B-Protocol
Neighbor	I-Protocol
Discovery	I-Protocol
(	O
SEND	B-Protocol
)	O
is	O
an	O
extension	O
of	O
NDP	B-Protocol
with	O
extra	O
security	O
.	O
</s>
<s>
Multicast	B-Protocol
Listener	I-Protocol
Discovery	I-Protocol
(	O
MLD	B-Protocol
)	O
is	O
used	O
by	O
IPv6	B-Protocol
routers	O
for	O
discovering	O
multicast	O
listeners	O
on	O
a	O
directly	O
attached	O
link	O
,	O
much	O
like	O
Internet	B-Protocol
Group	I-Protocol
Management	I-Protocol
Protocol	I-Protocol
(	O
IGMP	B-Protocol
)	O
is	O
used	O
in	O
IPv4	B-Protocol
.	O
</s>
<s>
Multicast	B-Protocol
Router	I-Protocol
Discovery	I-Protocol
(	O
MRD	B-Protocol
)	O
allows	O
the	O
discovery	O
of	O
multicast	O
routers	O
.	O
</s>
<s>
ICMPv6	B-Protocol
messages	O
may	O
be	O
classified	O
as	O
error	O
messages	O
and	O
information	O
messages	O
.	O
</s>
<s>
ICMPv6	B-Protocol
messages	O
are	O
transported	O
by	O
IPv6	B-Protocol
packets	O
in	O
which	O
the	O
IPv6	B-Protocol
Next	O
Header	O
value	O
for	O
ICMPv6	B-Protocol
is	O
set	O
to	O
the	O
value	O
58	O
.	O
</s>
<s>
The	O
ICMPv6	B-Protocol
message	O
consists	O
of	O
a	O
header	O
and	O
the	O
protocol	O
payload	O
.	O
</s>
<s>
The	O
header	O
contains	O
only	O
three	O
fields	O
:	O
type	O
(	O
8	O
bits	O
)	O
,	O
code	O
(	O
8	O
bits	O
)	O
,	O
and	O
checksum	B-Algorithm
(	O
16	O
bits	O
)	O
.	O
</s>
<s>
The	O
checksum	B-Algorithm
field	O
provides	O
a	O
minimal	O
level	O
of	O
integrity	O
verification	O
for	O
the	O
ICMP	B-Protocol
message	O
.	O
</s>
<s>
Some	O
messages	O
serve	O
the	O
same	O
purpose	O
as	O
the	O
correspondingly	O
named	O
ICMP	B-Protocol
message	O
types	O
.	O
</s>
<s>
Type	O
Code	O
Value	O
Meaning	O
Value	O
Meaning	O
ICMPv6	B-Protocol
Error	O
Messages	O
1	O
Destination	O
unreachable	O
0	O
no	O
route	O
to	O
destination	O
1	O
communication	O
with	O
destination	O
administratively	O
prohibited	O
2	O
beyond	O
scope	O
of	O
source	O
address	O
3	O
address	O
unreachable	O
4	O
port	O
unreachable	O
5	O
source	O
address	O
failed	O
ingress/egress	O
policy	O
6	O
reject	O
route	O
to	O
destination	O
7	O
Error	O
in	O
Source	O
Routing	O
Header	O
2	O
Packet	O
too	O
big	O
0	O
3	O
Time	O
exceeded	O
0	O
hop	O
limit	O
exceeded	O
in	O
transit	O
1	O
fragment	O
reassembly	O
time	O
exceeded	O
4	O
Parameter	O
problem	O
0	O
erroneous	O
header	O
field	O
encountered	O
1	O
unrecognized	O
Next	O
Header	O
type	O
encountered	O
2	O
unrecognized	O
IPv6	B-Protocol
option	O
encountered	O
100	O
Private	O
experimentation	O
101	O
Private	O
experimentation	O
127	O
Reserved	O
for	O
expansion	O
of	O
ICMPv6	B-Protocol
error	O
messages	O
ICMPv6	B-Protocol
Informational	O
Messages	O
128	O
Echo	B-Protocol
Request	I-Protocol
0	O
129	O
Echo	B-Protocol
Reply	I-Protocol
0	O
130	O
Multicast	O
Listener	O
Query	O
(	O
MLD	B-Protocol
)	O
0	O
There	O
are	O
two	O
subtypes	O
of	O
Multicast	O
Listener	O
Query	O
messages	O
:	O
</s>
<s>
These	O
two	O
subtypes	O
are	O
differentiated	O
by	O
the	O
contents	O
of	O
the	O
Multicast	O
Address	O
field	O
,	O
as	O
described	O
in	O
section	O
3.6	O
of	O
RFC	O
2710	O
131	O
Multicast	O
Listener	O
Report	O
(	O
MLD	B-Protocol
)	O
0	O
132	O
Multicast	O
Listener	O
Done	O
(	O
MLD	B-Protocol
)	O
0	O
133	O
Router	O
Solicitation	O
(	O
NDP	B-Protocol
)	O
0	O
134	O
Router	O
Advertisement	O
(	O
NDP	B-Protocol
)	O
0	O
135	O
Neighbor	O
Solicitation	O
(	O
NDP	B-Protocol
)	O
0	O
136	O
Neighbor	O
Advertisement	O
(	O
NDP	B-Protocol
)	O
0	O
137	O
Redirect	O
Message	O
(	O
NDP	B-Protocol
)	O
0	O
138	O
Router	O
Renumbering	O
0	O
Router	O
Renumbering	O
Command	O
1	O
Router	O
Renumbering	O
Result	O
255	O
Sequence	B-Protocol
Number	I-Protocol
Reset	O
139	O
ICMP	B-Protocol
Node	O
Information	O
Query	O
0	O
The	O
Data	O
field	O
contains	O
an	O
IPv6	B-Protocol
address	O
which	O
is	O
the	O
Subject	O
of	O
this	O
Query	O
.	O
</s>
<s>
2	O
The	O
Data	O
field	O
contains	O
an	O
IPv4	B-Protocol
address	O
which	O
is	O
the	O
Subject	O
of	O
this	O
Query	O
.	O
</s>
<s>
140	O
ICMP	B-Protocol
Node	O
Information	O
Response	O
0	O
A	O
successful	O
reply	O
.	O
</s>
<s>
The	O
current	O
complete	O
list	O
of	O
assigned	O
ICMPv6	B-Protocol
types	O
can	O
be	O
found	O
at	O
this	O
link	O
:	O
.	O
</s>
<s>
ICMPv6	B-Protocol
provides	O
a	O
minimal	O
level	O
of	O
message	O
integrity	O
verification	O
by	O
the	O
inclusion	O
of	O
a	O
16-bit	O
checksum	B-Algorithm
in	O
its	O
header	O
.	O
</s>
<s>
The	O
checksum	B-Algorithm
is	O
calculated	O
starting	O
with	O
a	O
pseudo-header	O
of	O
IPv6	B-Protocol
header	O
fields	O
according	O
to	O
the	O
IPv6	B-Protocol
standard	O
,	O
which	O
consists	O
of	O
the	O
source	O
and	O
destination	O
addresses	O
,	O
the	O
packet	O
length	O
and	O
the	O
next	O
header	O
field	O
,	O
the	O
latter	O
of	O
which	O
is	O
set	O
to	O
the	O
value	O
58	O
.	O
</s>
<s>
Following	O
this	O
pseudo	O
header	O
,	O
the	O
checksum	B-Algorithm
is	O
continued	O
with	O
the	O
ICMPv6	B-Protocol
message	O
.	O
</s>
<s>
The	O
checksum	B-Algorithm
computation	O
is	O
performed	O
according	O
to	O
Internet	O
protocol	O
standards	O
using	O
16-bit	O
ones	O
 '	O
complement	O
summation	O
,	O
followed	O
by	O
a	O
final	O
ones	O
 '	O
complement	O
of	O
the	O
checksum	B-Algorithm
itself	O
and	O
inserting	O
it	O
into	O
the	O
checksum	B-Algorithm
field	O
.	O
</s>
<s>
Note	O
that	O
this	O
differs	O
from	O
the	O
way	O
it	O
is	O
calculated	O
for	O
IPv4	B-Protocol
in	O
ICMP	B-Protocol
,	O
but	O
is	O
similar	O
to	O
the	O
calculation	O
done	O
in	O
TCP	B-Protocol
.	O
</s>
<s>
When	O
an	O
ICMPv6	B-Protocol
node	O
receives	O
a	O
packet	O
,	O
it	O
must	O
undertake	O
actions	O
that	O
depend	O
on	O
the	O
type	O
of	O
message	O
.	O
</s>
<s>
The	O
ICMPv6	B-Protocol
protocol	O
must	O
limit	O
the	O
number	O
of	O
error	O
messages	O
sent	O
to	O
the	O
same	O
destination	O
to	O
avoid	O
network	O
overloading	O
.	O
</s>
<s>
For	O
example	O
,	O
if	O
a	O
node	O
continues	O
to	O
forward	O
erroneous	O
packets	O
,	O
ICMP	B-Protocol
will	O
signal	O
the	O
error	O
to	O
the	O
first	O
packet	O
and	O
then	O
do	O
so	O
periodically	O
,	O
with	O
a	O
fixed	O
minimum	O
period	O
or	O
with	O
a	O
fixed	O
network	O
maximum	O
load	O
.	O
</s>
<s>
An	O
ICMP	B-Protocol
error	O
message	O
must	O
never	O
be	O
sent	O
in	O
response	O
to	O
another	O
ICMP	B-Protocol
error	O
message	O
.	O
</s>
