<s>
The	O
Echo	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
862	O
.	O
</s>
<s>
It	O
was	O
originally	O
proposed	O
for	O
testing	O
and	O
measurement	O
of	O
round-trip	O
times	O
in	O
IP	B-Protocol
networks	I-Protocol
.	O
</s>
<s>
A	O
host	O
may	O
connect	O
to	O
a	O
server	O
that	O
supports	O
the	O
Echo	B-Protocol
Protocol	I-Protocol
using	O
the	O
Transmission	B-Protocol
Control	I-Protocol
Protocol	I-Protocol
(	O
TCP	O
)	O
or	O
the	O
User	B-Protocol
Datagram	I-Protocol
Protocol	I-Protocol
(	O
UDP	O
)	O
on	O
the	O
well-known	O
port	B-Protocol
number	I-Protocol
7	O
.	O
</s>
<s>
On	O
UNIX-like	B-Operating_System
operating	I-Operating_System
systems	I-Operating_System
an	O
echo	B-Protocol
server	I-Protocol
is	O
built	O
into	O
the	O
inetd	B-Protocol
family	O
of	O
daemons	B-Operating_System
.	O
</s>
<s>
It	O
may	O
be	O
enabled	O
by	O
adding	O
the	O
following	O
lines	O
to	O
the	O
file	O
and	O
telling	O
inetd	B-Protocol
to	O
reload	O
its	O
configuration	O
:	O
</s>
<s>
On	O
various	O
routers	O
,	O
this	O
TCP	O
or	O
UDP	O
port	O
7	O
for	O
the	O
Echo	B-Protocol
Protocol	I-Protocol
for	O
relaying	O
ICMP	B-Protocol
datagrams	O
(	O
or	O
port	O
9	O
for	O
the	O
Discard	B-Protocol
Protocol	I-Protocol
)	O
is	O
also	O
configured	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>
