<s>
The	O
TCP	B-Protocol
Port	I-Protocol
Service	I-Protocol
Multiplexer	I-Protocol
(	O
TCPMUX	B-Protocol
)	O
is	O
a	O
little-used	O
Internet	O
protocol	O
defined	O
in	O
.	O
</s>
<s>
The	O
specification	O
describes	O
a	O
multiplexing	B-Architecture
service	O
that	O
may	O
be	O
accessed	O
with	O
a	O
network	O
protocol	O
to	O
contact	O
any	O
one	O
of	O
a	O
number	O
of	O
available	O
TCP	B-Protocol
services	O
of	O
a	O
host	O
on	O
a	O
single	O
,	O
well-known	O
port	B-Protocol
number	I-Protocol
.	O
</s>
<s>
The	O
specification	O
of	O
TCPMUX	B-Protocol
,	O
RFC	O
1078	O
,	O
was	O
deprecated	O
in	O
2016	O
by	O
for	O
technical	O
reasons	O
and	O
lack	O
of	O
use	O
in	O
the	O
Internet	O
.	O
</s>
<s>
A	O
host	O
may	O
connect	O
to	O
a	O
server	O
that	O
supports	O
the	O
TCPMUX	B-Protocol
protocol	O
on	O
TCP	B-Protocol
port	I-Protocol
1	O
.	O
</s>
<s>
Enabling	O
TCPMUX	B-Protocol
on	O
a	O
server	O
enables	O
an	O
attacker	O
to	O
easily	O
find	O
out	O
the	O
services	O
running	O
on	O
the	O
host	O
,	O
either	O
by	O
using	O
the	O
"	O
HELP	O
"	O
command	O
or	O
by	O
requesting	O
a	O
large	O
number	O
of	O
services	O
.	O
</s>
<s>
Because	O
TCPMUX	B-Protocol
allows	O
someone	O
to	O
use	O
any	O
service	O
only	O
by	O
accessing	O
port	B-Protocol
number	I-Protocol
1	O
,	O
the	O
protocol	O
makes	O
it	O
difficult	O
to	O
apply	O
traditional	O
port-based	O
firewall	O
rules	O
that	O
block	O
access	O
from	O
certain	O
or	O
all	O
hosts	O
to	O
specific	O
services	O
.	O
</s>
