<s>
In	O
computing	O
,	O
traceroute	B-Protocol
and	O
tracert	B-Protocol
are	O
computer	B-Architecture
network	I-Architecture
diagnostic	O
commands	B-Application
for	O
displaying	O
possible	O
routes	O
(	O
paths	O
)	O
and	O
measuring	O
transit	O
delays	O
of	O
packets	B-Protocol
across	O
an	O
Internet	B-Protocol
Protocol	I-Protocol
(	O
IP	O
)	O
network	O
.	O
</s>
<s>
The	O
history	O
of	O
the	O
route	O
is	O
recorded	O
as	O
the	O
round-trip	O
times	O
of	O
the	O
packets	B-Protocol
received	O
from	O
each	O
successive	O
host	O
(	O
remote	O
node	O
)	O
in	O
the	O
route	O
(	O
path	O
)	O
;	O
the	O
sum	O
of	O
the	O
mean	O
times	O
in	O
each	O
hop	B-Protocol
is	O
a	O
measure	O
of	O
the	O
total	O
time	O
spent	O
to	O
establish	O
the	O
connection	O
.	O
</s>
<s>
Traceroute	B-Protocol
proceeds	O
unless	O
all	O
(	O
usually	O
three	O
)	O
sent	O
packets	B-Protocol
are	O
lost	O
more	O
than	O
twice	O
;	O
then	O
the	O
connection	O
is	O
lost	O
and	O
the	O
route	O
cannot	O
be	O
evaluated	O
.	O
</s>
<s>
Ping	B-Protocol
,	O
on	O
the	O
other	O
hand	O
,	O
only	O
computes	O
the	O
final	O
round-trip	O
times	O
from	O
the	O
destination	O
point	O
.	O
</s>
<s>
For	O
Internet	B-Protocol
Protocol	I-Protocol
Version	I-Protocol
6	I-Protocol
(	O
IPv6	B-Protocol
)	O
the	O
tool	O
sometimes	O
has	O
the	O
name	O
traceroute6	B-Protocol
and	O
tracert6	B-Protocol
.	O
</s>
<s>
The	O
command	B-Application
traceroute	B-Protocol
is	O
available	O
on	O
many	O
modern	O
operating	B-General_Concept
systems	I-General_Concept
.	O
</s>
<s>
On	O
Unix-like	B-Operating_System
systems	I-Operating_System
such	O
as	O
FreeBSD	B-Operating_System
,	O
macOS	B-Application
,	O
and	O
Linux	B-Application
it	O
is	O
available	O
as	O
a	O
command	B-Application
line	O
tool	O
.	O
</s>
<s>
Traceroute	B-Protocol
is	O
also	O
graphically	O
accessible	O
in	O
macOS	B-Application
within	O
the	O
Network	O
Utilities	O
suite	O
;	O
these	O
utilities	O
have	O
been	O
deprecated	O
since	O
the	O
release	O
of	O
macOS	B-Operating_System
Big	I-Operating_System
Sur	I-Operating_System
.	O
</s>
<s>
Microsoft	B-Application
Windows	I-Application
and	O
ReactOS	B-Application
provide	O
a	O
program	O
named	O
tracert	B-Protocol
that	O
performs	O
the	O
same	O
route-tracing	O
function	O
.	O
</s>
<s>
Windows	O
NT-based	O
operating	B-General_Concept
systems	I-General_Concept
also	O
provide	O
PathPing	B-Protocol
,	O
which	O
combines	O
the	O
functionality	O
of	O
ping	B-Protocol
with	O
that	O
of	O
tracert	B-Protocol
.	O
</s>
<s>
The	O
ReactOS	B-Application
version	O
was	O
developed	O
by	O
Ged	O
Murphy	O
and	O
is	O
licensed	O
under	O
the	O
GPL	B-License
.	O
</s>
<s>
On	O
Unix-like	B-Operating_System
operating	I-Operating_System
systems	I-Operating_System
,	O
traceroute	B-Protocol
sends	O
,	O
by	O
default	O
,	O
a	O
sequence	O
of	O
User	B-Protocol
Datagram	I-Protocol
Protocol	I-Protocol
(	O
UDP	B-Protocol
)	O
packets	B-Protocol
,	O
with	O
destination	O
port	B-Protocol
numbers	I-Protocol
ranging	O
from	O
33434	O
to	O
33534	O
;	O
the	O
implementations	O
of	O
traceroute	B-Protocol
shipped	O
with	O
Linux	B-Application
,	O
FreeBSD	B-Operating_System
,	O
NetBSD	B-Device
,	O
OpenBSD	B-Operating_System
,	O
DragonFly	B-Application
BSD	I-Application
,	O
and	O
macOS	B-Application
include	O
an	O
option	O
to	O
use	O
ICMP	B-Protocol
Echo	I-Protocol
Request	I-Protocol
packets	B-Protocol
(	O
-I	O
)	O
,	O
or	O
any	O
arbitrary	O
protocol	O
(	O
-P	O
)	O
such	O
as	O
UDP	B-Protocol
,	O
TCP	O
using	O
TCP	O
SYN	O
packets	B-Protocol
,	O
or	O
ICMP	O
.	O
</s>
<s>
On	O
Windows	B-Application
,	O
tracert	B-Protocol
sends	O
ICMP	B-Protocol
Echo	I-Protocol
Request	I-Protocol
packets	B-Protocol
,	O
rather	O
than	O
the	O
UDP	B-Protocol
packets	I-Protocol
traceroute	B-Protocol
sends	O
by	O
default	O
.	O
</s>
<s>
The	O
time-to-live	B-Protocol
(	O
TTL	B-Protocol
)	O
value	O
,	O
also	O
known	O
as	O
hop	B-Protocol
limit	I-Protocol
,	O
is	O
used	O
in	O
determining	O
the	O
intermediate	O
routers	O
being	O
traversed	O
towards	O
the	O
destination	O
.	O
</s>
<s>
Traceroute	B-Protocol
sends	O
packets	B-Protocol
with	O
TTL	B-Protocol
values	O
that	O
gradually	O
increase	O
from	O
packet	B-Protocol
to	O
packet	B-Protocol
,	O
starting	O
with	O
TTL	B-Protocol
value	O
of	O
one	O
.	O
</s>
<s>
Routers	O
decrement	O
TTL	B-Protocol
values	O
of	O
packets	B-Protocol
by	O
one	O
when	O
routing	O
and	O
discard	O
packets	B-Protocol
whose	O
TTL	B-Protocol
value	O
has	O
reached	O
zero	O
,	O
returning	O
the	O
ICMP	O
error	O
message	O
ICMP	O
Time	O
Exceeded	O
.	O
</s>
<s>
For	O
the	O
first	O
set	O
of	O
packets	B-Protocol
,	O
the	O
first	O
router	O
receives	O
the	O
packet	B-Protocol
,	O
decrements	O
the	O
TTL	B-Protocol
value	O
and	O
drops	O
the	O
packet	B-Protocol
because	O
it	O
then	O
has	O
TTL	B-Protocol
value	O
zero	O
.	O
</s>
<s>
The	O
next	O
set	O
of	O
packets	B-Protocol
are	O
given	O
a	O
TTL	B-Protocol
value	O
of	O
two	O
,	O
so	O
the	O
first	O
router	O
forwards	O
the	O
packets	B-Protocol
,	O
but	O
the	O
second	O
router	O
drops	O
them	O
and	O
replies	O
with	O
ICMP	O
Time	O
Exceeded	O
.	O
</s>
<s>
Proceeding	O
in	O
this	O
way	O
,	O
traceroute	B-Protocol
uses	O
the	O
returned	O
ICMP	O
Time	O
Exceeded	O
messages	O
to	O
build	O
a	O
list	O
of	O
routers	O
that	O
packets	B-Protocol
traverse	O
,	O
until	O
the	O
destination	O
is	O
reached	O
and	O
returns	O
an	O
ICMP	O
Destination	O
Unreachable	O
message	O
if	O
UDP	B-Protocol
packets	I-Protocol
are	O
being	O
used	O
or	O
an	O
ICMP	B-Protocol
Echo	I-Protocol
Reply	I-Protocol
message	O
if	O
ICMP	B-Protocol
Echo	I-Protocol
messages	O
are	O
being	O
used	O
.	O
</s>
<s>
The	O
timestamp	O
values	O
returned	O
for	O
each	O
router	O
along	O
the	O
path	O
are	O
the	O
delay	O
(	O
latency	O
)	O
values	O
,	O
typically	O
measured	O
in	O
milliseconds	O
for	O
each	O
packet	B-Protocol
.	O
</s>
<s>
If	O
a	O
packet	B-Protocol
is	O
not	O
acknowledged	O
within	O
the	O
expected	O
interval	O
,	O
an	O
asterisk	O
is	O
displayed	O
.	O
</s>
<s>
The	O
Internet	B-Protocol
Protocol	I-Protocol
does	O
not	O
require	O
packets	B-Protocol
to	O
take	O
the	O
same	O
route	O
towards	O
a	O
particular	O
destination	O
,	O
thus	O
hosts	O
listed	O
might	O
be	O
hosts	O
that	O
other	O
packets	B-Protocol
have	O
traversed	O
.	O
</s>
<s>
If	O
the	O
host	O
at	O
hop	B-Protocol
#N	O
does	O
not	O
reply	O
,	O
the	O
hop	B-Protocol
is	O
skipped	O
in	O
the	O
output	O
.	O
</s>
<s>
If	O
a	O
network	O
has	O
a	O
firewall	O
and	O
operates	O
both	O
Windows	B-Application
and	O
Unix-like	B-Operating_System
systems	I-Operating_System
,	O
more	O
than	O
one	O
protocol	O
must	O
be	O
enabled	O
inbound	O
through	O
the	O
firewall	O
for	O
traceroute	B-Protocol
to	O
work	O
and	O
receive	O
replies	O
.	O
</s>
<s>
Some	O
traceroute	B-Protocol
implementations	O
use	O
TCP	O
packets	B-Protocol
,	O
such	O
as	O
tcptraceroute	O
and	O
layer	B-Protocol
four	I-Protocol
traceroute	I-Protocol
(	O
lft	O
)	O
.	O
</s>
<s>
PathPing	B-Protocol
is	O
a	O
utility	O
introduced	O
with	O
Windows	B-Device
NT	I-Device
that	O
combines	O
ping	B-Protocol
and	O
traceroute	B-Protocol
functionality	O
.	O
</s>
<s>
MTR	B-Protocol
is	O
an	O
enhanced	O
version	O
of	O
ICMP	O
traceroute	B-Protocol
available	O
for	O
Unix-like	B-Operating_System
and	O
Windows	B-Application
systems	O
.	O
</s>
<s>
The	O
various	O
implementations	O
of	O
traceroute	B-Protocol
all	O
rely	O
on	O
ICMP	O
Time	O
Exceeded	O
(	O
type	O
11	O
)	O
packets	B-Protocol
being	O
sent	O
to	O
the	O
source	O
.	O
</s>
<s>
On	O
Linux	B-Application
,	O
tracepath	O
is	O
a	O
utility	O
similar	O
to	O
traceroute	B-Protocol
,	O
with	O
the	O
primary	O
difference	O
of	O
not	O
requiring	O
superuser	B-Application
privileges	O
.	O
</s>
<s>
Cisco	O
's	O
implementation	O
of	O
traceroute	B-Protocol
also	O
uses	O
a	O
sequence	O
of	O
UDP	B-Protocol
datagrams	O
,	O
each	O
with	O
incrementing	O
TTL	B-Protocol
values	O
,	O
to	O
an	O
invalid	O
port	B-Protocol
number	I-Protocol
at	O
the	O
remote	O
host	O
;	O
by	O
default	O
,	O
UDP	B-Protocol
port	O
33434	O
is	O
used	O
.	O
</s>
<s>
An	O
extended	O
version	O
of	O
this	O
command	B-Application
(	O
known	O
as	O
the	O
extended	O
traceroute	B-Protocol
command	B-Application
)	O
can	O
change	O
the	O
destination	O
port	B-Protocol
number	I-Protocol
used	O
by	O
the	O
UDP	B-Protocol
probe	O
messages	O
.	O
</s>
<s>
Most	O
implementations	O
include	O
at	O
least	O
options	O
to	O
specify	O
the	O
number	O
of	O
queries	O
to	O
send	O
per	O
hop	B-Protocol
,	O
time	O
to	O
wait	O
for	O
a	O
response	O
,	O
the	O
hop	B-Protocol
limit	I-Protocol
and	O
port	O
to	O
use	O
.	O
</s>
<s>
Invoking	O
traceroute	B-Protocol
with	O
no	O
specified	O
options	O
displays	O
the	O
list	O
of	O
available	O
options	O
,	O
while	O
man	O
traceroute	B-Protocol
presents	O
more	O
details	O
,	O
including	O
the	O
displayed	O
error	O
flags	O
.	O
</s>
<s>
An	O
example	O
on	O
Linux	B-Application
:	O
</s>
<s>
In	O
the	O
example	O
above	O
,	O
selected	O
options	O
are	O
to	O
wait	O
for	O
three	O
seconds	O
(	O
instead	O
of	O
five	O
)	O
,	O
send	O
out	O
only	O
one	O
query	O
to	O
each	O
hop	B-Protocol
(	O
instead	O
of	O
three	O
)	O
,	O
limit	O
the	O
maximum	O
number	O
of	O
hops	B-Protocol
to	O
16	O
before	O
giving	O
up	O
(	O
instead	O
of	O
30	O
)	O
,	O
with	O
example.com	O
as	O
the	O
final	O
host	O
.	O
</s>
<s>
Traceroute	B-Protocol
can	O
be	O
used	O
to	O
help	O
identify	O
incorrect	O
routing	O
table	O
definitions	O
or	O
firewalls	O
that	O
may	O
be	O
blocking	O
ICMP	O
traffic	O
,	O
A	O
correct	O
traceroute	B-Protocol
response	O
does	O
not	O
guarantee	O
connectivity	O
for	O
applications	O
as	O
a	O
firewall	O
may	O
permit	O
ICMP	O
packets	B-Protocol
but	O
not	O
permit	O
packets	B-Protocol
of	O
other	O
protocols	O
.	O
</s>
<s>
Traceroute	B-Protocol
is	O
also	O
used	O
by	O
penetration	O
testers	O
to	O
gather	O
information	O
about	O
network	B-Architecture
infrastructure	I-Architecture
and	O
IP	O
address	O
ranges	O
around	O
a	O
given	O
host	O
.	O
</s>
<s>
The	O
traceroute	B-Protocol
manual	B-Protocol
page	I-Protocol
states	O
that	O
the	O
original	O
traceroute	B-Protocol
program	I-Protocol
was	O
written	O
by	O
Van	O
Jacobson	O
in	O
1987	O
from	O
a	O
suggestion	O
by	O
Steve	O
Deering	O
,	O
with	O
particularly	O
cogent	O
suggestions	O
or	O
fixes	O
from	O
C	O
.	O
Philip	O
Wood	O
,	O
Tim	O
Seaver	O
and	O
Ken	O
Adelman	O
.	O
</s>
<s>
The	O
author	O
of	O
the	O
ping	B-Protocol
program	O
,	O
Mike	O
Muuss	O
,	O
states	O
on	O
his	O
website	O
that	O
traceroute	B-Protocol
was	O
written	O
using	O
kernel	O
ICMP	O
support	O
that	O
he	O
had	O
earlier	O
coded	O
to	O
enable	O
raw	O
ICMP	O
sockets	O
when	O
he	O
first	O
wrote	O
the	O
ping	B-Protocol
program	O
.	O
</s>
<s>
Traceroute	B-Protocol
limitations	O
are	O
well	O
known	O
and	O
should	O
be	O
taken	O
into	O
account	O
when	O
using	O
the	O
tool	O
.	O
</s>
<s>
For	O
example	O
,	O
traceroute	B-Protocol
does	O
not	O
discover	O
paths	O
at	O
the	O
router	O
level	O
,	O
but	O
at	O
the	O
interface	O
level	O
.	O
</s>
<s>
In	O
the	O
presence	O
of	O
traffic	O
load	B-Application
balancing	I-Application
,	O
traceroute	B-Protocol
may	O
indicate	O
a	O
path	O
that	O
does	O
not	O
actually	O
exist	O
;	O
to	O
minimize	O
this	O
problem	O
there	O
is	O
a	O
traceroute	B-Protocol
modification	O
called	O
Paris-traceroute	O
,	O
which	O
maintains	O
the	O
flow	O
identifier	O
of	O
the	O
probes	O
to	O
avoid	O
load	B-Application
balancing	I-Application
.	O
</s>
