<s>
The	O
Discard	B-Protocol
Protocol	I-Protocol
is	O
a	O
service	O
in	O
the	O
Internet	B-Protocol
Protocol	I-Protocol
Suite	I-Protocol
defined	O
in	O
RFC	O
863	O
.	O
</s>
<s>
A	O
host	O
may	O
send	O
data	O
to	O
a	O
host	O
that	O
supports	O
the	O
Discard	B-Protocol
Protocol	I-Protocol
on	O
either	O
Transmission	B-Protocol
Control	I-Protocol
Protocol	I-Protocol
(	O
TCP	O
)	O
or	O
User	B-Protocol
Datagram	I-Protocol
Protocol	I-Protocol
(	O
UDP	O
)	O
port	B-Protocol
number	I-Protocol
9	O
.	O
</s>
<s>
For	O
this	O
reason	O
,	O
UDP	O
is	O
usually	O
used	O
,	O
but	O
TCP	O
allows	O
the	O
services	O
to	O
be	O
accessible	O
on	O
session-oriented	O
connections	O
(	O
for	O
example	O
via	O
HTTP	B-Protocol
proxies	O
or	O
some	O
virtual	B-Application
private	I-Application
network	I-Application
(	O
VPN	B-Application
)	O
)	O
.	O
</s>
<s>
On	O
most	O
Unix-like	B-Operating_System
operating	I-Operating_System
systems	I-Operating_System
a	O
discard	B-Protocol
server	O
is	O
built	O
into	O
the	O
inetd	B-Protocol
(	O
or	O
xinetd	B-Operating_System
)	O
daemon	B-Operating_System
.	O
</s>
<s>
The	O
discard	B-Protocol
service	O
is	O
usually	O
not	O
enabled	O
by	O
default	O
.	O
</s>
<s>
The	O
Discard	B-Protocol
Protocol	I-Protocol
is	O
the	O
TCP/UDP	O
equivalent	O
of	O
the	O
Unix	O
file-system	O
node	O
/dev/null	B-Operating_System
.	O
</s>
<s>
On	O
various	O
routers	O
,	O
this	O
TCP	O
or	O
UDP	O
port	O
9	O
for	O
the	O
Discard	B-Protocol
Protocol	I-Protocol
(	O
or	O
port	O
7	O
for	O
the	O
Echo	B-Protocol
Protocol	I-Protocol
relaying	O
ICMP	B-Protocol
datagrams	O
)	O
is	O
also	O
used	O
by	O
default	O
as	O
a	O
proxy	O
to	O
relay	O
Wake-on-LAN	O
(	O
WOL	O
)	O
magic	O
packets	O
from	O
the	O
Internet	O
to	O
hosts	O
on	O
the	O
local	O
network	O
in	O
order	O
to	O
wake	O
them	O
up	O
remotely	O
(	O
these	O
hosts	O
must	O
also	O
have	O
their	O
network	O
adapter	O
configured	O
to	O
accept	O
WOL	O
datagrams	O
and	O
the	O
router	O
must	O
have	O
this	O
proxy	O
setting	O
enabled	O
,	O
and	O
possibly	O
also	O
a	O
configuration	O
of	O
forwarding	O
rules	O
in	O
its	O
embedded	O
firewall	B-Application
to	O
open	O
these	O
ports	O
on	O
the	O
Internet	O
side	O
)	O
.	O
</s>
