<s>
The	O
port	B-Protocol
mapper	I-Protocol
(	O
rpc.portmap	O
or	O
just	O
portmap	B-Protocol
,	O
or	O
rpcbind	B-Protocol
)	O
is	O
an	O
Open	B-Protocol
Network	I-Protocol
Computing	I-Protocol
Remote	I-Protocol
Procedure	I-Protocol
Call	I-Protocol
(	O
ONC	B-Protocol
RPC	I-Protocol
)	O
service	O
that	O
runs	O
on	O
network	O
nodes	O
that	O
provide	O
other	O
ONC	B-Protocol
RPC	I-Protocol
services	O
.	O
</s>
<s>
Version	O
2	O
of	O
the	O
port	B-Protocol
mapper	I-Protocol
protocol	O
maps	O
ONC	B-Protocol
RPC	I-Protocol
program	O
number/version	O
number	O
pairs	O
to	O
the	O
network	O
port	O
number	O
for	O
that	O
version	O
of	O
that	O
program	O
.	O
</s>
<s>
When	O
an	O
ONC	B-Protocol
RPC	I-Protocol
server	O
is	O
started	O
,	O
it	O
will	O
tell	O
the	O
port	B-Protocol
mapper	I-Protocol
,	O
for	O
each	O
particular	O
program	O
number/version	O
number	O
pair	O
it	O
implements	O
for	O
a	O
particular	O
transport	O
protocol	O
(	O
TCP	B-Protocol
or	O
UDP	B-Protocol
)	O
,	O
what	O
port	O
number	O
it	O
is	O
using	O
for	O
that	O
particular	O
program	O
number/version	O
number	O
pair	O
on	O
that	O
transport	O
protocol	O
.	O
</s>
<s>
Clients	O
wishing	O
to	O
make	O
an	O
ONC	B-Protocol
RPC	I-Protocol
call	O
to	O
a	O
particular	O
version	O
of	O
a	O
particular	O
ONC	B-Protocol
RPC	I-Protocol
service	O
must	O
first	O
contact	O
the	O
port	B-Protocol
mapper	I-Protocol
on	O
the	O
server	O
machine	O
to	O
determine	O
the	O
actual	O
TCP	B-Protocol
or	O
UDP	B-Protocol
port	O
to	O
use	O
.	O
</s>
<s>
Versions	O
3	O
and	O
4	O
of	O
the	O
protocol	O
,	O
called	O
the	O
rpcbind	B-Protocol
protocol	O
,	O
map	O
a	O
program	O
number/version	O
number	O
pair	O
,	O
and	O
an	O
indicator	O
that	O
specifies	O
a	O
transport	O
protocol	O
,	O
to	O
a	O
transport-layer	O
endpoint	O
address	O
for	O
that	O
program	O
number/version	O
number	O
pair	O
on	O
that	O
transport	O
protocol	O
.	O
</s>
<s>
The	O
port	B-Protocol
mapper	I-Protocol
service	O
always	O
uses	O
TCP	B-Protocol
or	O
UDP	B-Protocol
port	O
111	O
;	O
a	O
fixed	O
port	O
is	O
required	O
for	O
it	O
,	O
as	O
a	O
client	O
would	O
not	O
be	O
able	O
to	O
get	O
the	O
port	O
number	O
for	O
the	O
port	B-Protocol
mapper	I-Protocol
service	O
from	O
the	O
port	B-Protocol
mapper	I-Protocol
itself	O
.	O
</s>
<s>
The	O
port	B-Protocol
mapper	I-Protocol
must	O
be	O
started	O
before	O
any	O
other	O
RPC	O
servers	O
are	O
started	O
.	O
</s>
<s>
The	O
port	B-Protocol
mapper	I-Protocol
service	O
first	O
appeared	O
in	O
SunOS	B-Operating_System
2.0	O
.	O
</s>
<s>
For	O
example	O
,	O
it	O
shows	O
that	O
NFS	B-Protocol
is	O
running	O
,	O
both	O
version	O
2	O
and	O
3	O
,	O
and	O
can	O
be	O
reached	O
at	O
TCP	B-Protocol
port	O
2049	O
or	O
UDP	B-Protocol
port	O
2049	O
,	O
depending	O
on	O
what	O
transport	O
protocol	O
the	O
client	O
wants	O
to	O
use	O
,	O
and	O
that	O
the	O
mount	O
protocol	O
,	O
both	O
version	O
1	O
and	O
2	O
,	O
is	O
running	O
,	O
and	O
can	O
be	O
reached	O
at	O
UDP	B-Protocol
port	O
644	O
or	O
TCP	B-Protocol
port	O
645	O
,	O
depending	O
on	O
what	O
transport	O
protocol	O
the	O
client	O
wants	O
to	O
use	O
.	O
</s>
<s>
The	O
port	B-Protocol
mapper	I-Protocol
service	O
was	O
discovered	O
to	O
be	O
used	O
in	O
Distributed	O
Denial	O
of	O
Service	O
(	O
DDoS	O
)	O
attacks	O
and	O
Distributed	O
Reflective	O
Denial	O
of	O
Service	O
(	O
DRDoS	O
)	O
attacks	O
in	O
2015	O
.	O
</s>
<s>
By	O
using	O
a	O
spoofed	O
port	B-Protocol
mapper	I-Protocol
request	O
,	O
an	O
attacker	O
can	O
amplify	O
the	O
effects	O
on	O
a	O
target	O
because	O
a	O
portmap	B-Protocol
query	O
will	O
return	O
many	O
times	O
more	O
data	O
than	O
in	O
the	O
original	O
request	O
.	O
</s>
