<s>
Iftop	B-Application
is	O
a	O
free	B-Application
software	I-Application
command-line	O
system	B-Application
monitor	I-Application
tool	O
that	O
produces	O
a	O
frequently	O
updated	O
list	O
of	O
network	O
connections	O
.	O
</s>
<s>
By	O
default	O
,	O
the	O
connections	O
are	O
ordered	O
by	O
bandwidth	O
usage	O
,	O
with	O
only	O
the	O
"	O
top	B-Device
"	O
bandwidth	O
consumers	O
shown	O
.	O
</s>
<s>
It	O
is	O
analogous	O
to	O
top	B-Device
,	O
but	O
instead	O
of	O
system-wide	O
resource	O
monitoring	O
,	O
it	O
focuses	O
on	O
displaying	O
network	O
usage	O
and	O
statistics	O
.	O
</s>
<s>
iftop	B-Application
monitors	O
network	O
traffic	O
and	O
displays	O
a	O
table	O
of	O
current	O
bandwidth	O
usage	O
.	O
</s>
<s>
If	O
not	O
,	O
it	O
will	O
listen	O
on	O
the	O
first	O
interface	O
it	O
finds	O
that	O
appears	O
to	O
be	O
external	O
(	O
with	O
libpcap	B-Language
and	O
libncurses	B-Language
)	O
.	O
</s>
<s>
iftop	B-Application
must	O
be	O
run	O
with	O
sufficient	O
permissions	O
to	O
monitor	O
all	O
network	O
traffic	O
:	O
on	O
most	O
systems	O
this	O
means	O
that	O
it	O
must	O
be	O
run	O
as	O
a	O
root	B-Application
user	I-Application
using	O
the	O
sudo	B-Device
command	O
.	O
</s>
<s>
By	O
default	O
,	O
iftop	B-Application
will	O
look	O
up	O
hostnames	O
associated	O
with	O
addresses	O
and	O
counts	O
all	O
IP	O
packets	O
that	O
pass	O
through	O
the	O
filter	O
.	O
</s>
<s>
A	O
feature	O
of	O
iftop	B-Application
is	O
that	O
it	O
can	O
suppress	O
display	O
of	O
DNS	B-Protocol
traffic	O
by	O
using	O
a	O
filter	O
code	O
such	O
as	O
"	O
not	O
port	O
domain	O
"	O
,	O
or	O
switch	O
it	O
off	O
entirely	O
,	O
by	O
using	O
the	O
-n	O
option	O
or	O
by	O
pressing	O
"	O
n	O
"	O
when	O
the	O
program	O
is	O
running	O
.	O
</s>
