<s>
Layer	B-Protocol
Four	I-Protocol
Traceroute	I-Protocol
(	O
LFT	O
)	O
is	O
a	O
fast	O
,	O
multi-protocol	O
traceroute	B-Protocol
engine	O
,	O
that	O
also	O
implements	O
numerous	O
other	O
features	O
including	O
AS	B-Architecture
number	I-Architecture
lookups	O
through	O
regional	O
Internet	O
registries	O
and	O
other	O
reliable	O
sources	O
,	O
Loose	O
Source	O
Routing	O
,	O
firewall	B-Application
and	O
load	O
balancer	O
detection	O
,	O
etc	O
.	O
</s>
<s>
LFT	O
is	O
best	O
known	O
for	O
its	O
use	O
by	O
network	O
security	O
practitioners	O
to	O
trace	O
a	O
route	O
to	O
a	O
destination	O
host	O
through	O
many	O
configurations	O
of	O
packet-filters	O
/	O
firewalls	B-Application
,	O
and	O
to	O
detect	O
network	O
connectivity	O
,	O
performance	O
or	O
latency	O
problems	O
.	O
</s>
<s>
LFT	O
sends	O
various	O
TCP	B-Protocol
SYN	O
and	O
FIN	O
probes	O
(	O
differing	O
from	O
Van	O
Jacobson	O
's	O
UDP-based	O
method	O
)	O
or	O
UDP	B-Protocol
probes	O
utilizing	O
the	O
IP	B-Protocol
protocol	I-Protocol
time	B-Protocol
to	I-Protocol
live	I-Protocol
field	O
and	O
attempts	O
to	O
elicit	O
an	O
ICMP	B-Protocol
TIME_EXCEEDED	O
response	O
from	O
each	O
gateway	B-Application
along	O
the	O
path	O
to	O
some	O
host	O
.	O
</s>
<s>
LFT	O
also	O
listens	O
for	O
various	O
TCP	B-Protocol
,	O
UDP	B-Protocol
,	O
and	O
ICMP	B-Protocol
messages	O
along	O
the	O
way	O
to	O
assist	O
network	O
managers	O
in	O
ascertaining	O
per-protocol	O
heuristic	B-Protocol
routing	I-Protocol
information	O
,	O
and	O
can	O
optionally	O
retrieve	O
various	O
information	O
about	O
the	O
networks	O
it	O
traverses	O
.	O
</s>
<s>
The	O
operation	O
of	O
layer	B-Protocol
four	I-Protocol
traceroute	I-Protocol
is	O
described	O
in	O
detail	O
in	O
several	O
prominent	O
security	O
books	O
.	O
</s>
<s>
Renamed	O
as	O
a	O
result	O
of	O
confusion	O
with	O
fast	O
Fourier	O
transforms	O
,	O
lft	O
stands	O
for	O
layer	B-Protocol
four	I-Protocol
traceroute	I-Protocol
.	O
</s>
<s>
Results	O
are	O
often	O
referred	O
to	O
as	O
a	O
layer	B-Protocol
four	I-Protocol
trace	I-Protocol
.	O
</s>
