<s>
In	O
computer	B-Architecture
networking	I-Architecture
,	O
the	O
ICMP	O
Internet	B-Protocol
Router	I-Protocol
Discovery	O
Protocol	O
(	O
IRDP	O
)	O
,	O
also	O
called	O
the	O
Internet	B-Protocol
Router	I-Protocol
Discovery	O
Protocol	O
,	O
is	O
a	O
protocol	O
for	O
computer	O
hosts	O
to	O
discover	O
the	O
presence	O
and	O
location	O
of	O
routers	B-Protocol
on	O
their	O
IPv4	B-Protocol
local	B-General_Concept
area	I-General_Concept
network	I-General_Concept
.	O
</s>
<s>
Router	B-Protocol
discovery	O
is	O
useful	O
for	O
accessing	O
computer	O
systems	O
on	O
other	O
nonlocal	O
area	O
networks	O
.	O
</s>
<s>
The	O
IRDP	O
is	O
defined	O
by	O
the	O
IETF	O
RFC	O
1256	O
standard	O
,	O
with	O
the	O
Internet	B-Protocol
Control	I-Protocol
Message	I-Protocol
Protocol	I-Protocol
(	O
ICMP	O
)	O
upon	O
which	O
it	O
is	O
based	O
defined	O
in	O
IETF	O
RFC	O
792	O
.	O
</s>
<s>
To	O
enable	O
router	B-Protocol
discovery	O
,	O
the	O
IRDP	O
defines	O
two	O
kinds	O
of	O
ICMP	O
messages	O
:	O
</s>
<s>
The	O
ICMP	O
Router	B-Protocol
Solicitation	O
message	O
is	O
sent	O
from	O
a	O
computer	O
host	O
to	O
any	O
routers	B-Protocol
on	O
the	O
local	B-General_Concept
area	I-General_Concept
network	I-General_Concept
to	O
request	O
that	O
they	O
advertise	O
their	O
presence	O
on	O
the	O
network	O
.	O
</s>
<s>
The	O
ICMP	O
Router	B-Protocol
Advertisement	O
message	O
is	O
sent	O
by	O
a	O
router	B-Protocol
on	O
the	O
local	B-General_Concept
area	I-General_Concept
network	I-General_Concept
to	O
announce	O
its	O
IP	O
address	O
as	O
available	O
for	O
routing	O
.	O
</s>
<s>
In	O
response	O
,	O
one	O
or	O
more	O
routers	B-Protocol
may	O
send	O
advertisement	O
messages	O
.	O
</s>
<s>
If	O
there	O
is	O
more	O
than	O
one	O
router	B-Protocol
,	O
the	O
host	O
usually	O
picks	O
the	O
first	O
message	O
it	O
gets	O
and	O
adds	O
that	O
router	B-Protocol
to	O
its	O
routing	B-Protocol
table	I-Protocol
.	O
</s>
<s>
Independently	O
of	O
a	O
solicitation	O
,	O
a	O
router	B-Protocol
may	O
periodically	O
send	O
out	O
advertisement	O
messages	O
.	O
</s>
<s>
The	O
IRDP	O
strategy	O
has	O
been	O
used	O
in	O
the	O
development	O
of	O
the	O
IPv6	B-Protocol
neighbor	O
discovery	O
protocol	O
.	O
</s>
<s>
These	O
use	O
ICMPv6	B-Protocol
messages	O
,	O
the	O
IPv6	B-Protocol
analog	O
of	O
ICMP	O
messages	O
.	O
</s>
