<s>
Trivial	B-Device
File	I-Device
Transfer	I-Device
Protocol	I-Device
(	O
TFTP	B-Device
)	O
is	O
a	O
simple	O
lockstep	B-General_Concept
File	B-Protocol
Transfer	I-Protocol
Protocol	I-Protocol
which	O
allows	O
a	O
client	B-Protocol
to	O
get	O
a	O
file	O
from	O
or	O
put	O
a	O
file	O
onto	O
a	O
remote	O
host	B-Device
.	O
</s>
<s>
One	O
of	O
its	O
primary	O
uses	O
is	O
in	O
the	O
early	O
stages	O
of	O
nodes	O
booting	O
from	O
a	O
local	B-General_Concept
area	I-General_Concept
network	I-General_Concept
.	O
</s>
<s>
TFTP	B-Device
has	O
been	O
used	O
for	O
this	O
application	O
because	O
it	O
is	O
very	O
simple	O
to	O
implement	O
.	O
</s>
<s>
TFTP	B-Device
was	O
first	O
standardized	O
in	O
1981	O
and	O
the	O
current	O
specification	O
for	O
the	O
protocol	O
can	O
be	O
found	O
in	O
.	O
</s>
<s>
Due	O
to	O
its	O
simple	O
design	O
,	O
TFTP	B-Device
can	O
be	O
easily	O
implemented	O
by	O
code	O
with	O
a	O
small	O
memory	O
footprint	O
.	O
</s>
<s>
It	O
is	O
therefore	O
the	O
protocol	O
of	O
choice	O
for	O
the	O
initial	O
stages	O
of	O
any	O
network	B-Device
booting	I-Device
strategy	O
like	O
BOOTP	B-Device
,	O
PXE	B-Device
,	O
BSDP	B-Device
,	O
etc.	O
,	O
when	O
targeting	O
from	O
highly	O
resourced	O
computers	O
to	O
very	O
low	O
resourced	O
Single-board	B-Device
computers	I-Device
(	O
SBC	O
)	O
and	O
System	B-Architecture
on	I-Architecture
a	I-Architecture
Chip	I-Architecture
(	O
SoC	O
)	O
.	O
</s>
<s>
It	O
is	O
also	O
used	O
to	O
transfer	O
firmware	B-Application
images	O
and	O
configuration	O
files	O
to	O
network	O
appliances	O
like	O
routers	B-Protocol
,	O
firewalls	B-Application
,	O
IP	B-Device
phones	I-Device
,	O
etc	O
.	O
</s>
<s>
Today	O
,	O
TFTP	B-Device
is	O
virtually	O
unused	O
for	O
Internet	O
transfers	O
.	O
</s>
<s>
TFTP	B-Device
's	O
design	O
was	O
influenced	O
from	O
the	O
earlier	O
protocol	O
EFTP	B-Protocol
,	O
which	O
was	O
part	O
of	O
the	O
PARC	B-Protocol
Universal	I-Protocol
Packet	I-Protocol
protocol	I-Protocol
suite	I-Protocol
.	O
</s>
<s>
TFTP	B-Device
was	O
first	O
defined	O
in	O
1980	O
by	O
IEN	O
133	O
.	O
</s>
<s>
In	O
June	O
1981	O
The	O
TFTP	B-Device
Protocol	O
(	O
Revision	O
2	O
)	O
was	O
published	O
as	O
RFC	O
783	O
and	O
later	O
updated	O
in	O
July	O
1992	O
by	O
RFC	O
1350	O
which	O
fixed	O
among	O
other	O
things	O
the	O
Sorcerer	B-Protocol
's	I-Protocol
Apprentice	I-Protocol
Syndrome	I-Protocol
.	O
</s>
<s>
In	O
March	O
1995	O
the	O
TFTP	B-Device
Option	O
Extension	O
RFC	O
1782	O
updated	O
later	O
in	O
May	O
1998	O
by	O
RFC	O
2347	O
,	O
defined	O
the	O
option	O
negotiation	O
mechanism	O
which	O
establishes	O
the	O
framework	O
for	O
file	O
transfer	O
options	O
to	O
be	O
negotiated	O
prior	O
to	O
the	O
transfer	O
using	O
a	O
mechanism	O
which	O
is	O
consistent	O
with	O
TFTP	B-Device
's	O
original	O
specification	O
.	O
</s>
<s>
TFTP	B-Device
is	O
a	O
simple	O
protocol	O
for	O
transferring	O
files	O
,	O
implemented	O
on	O
top	O
of	O
the	O
UDP/IP	B-Protocol
protocols	O
using	O
well-known	O
port	O
number	O
69	O
.	O
</s>
<s>
TFTP	B-Device
was	O
designed	O
to	O
be	O
small	O
and	O
easy	O
to	O
implement	O
,	O
and	O
therefore	O
it	O
lacks	O
most	O
of	O
the	O
advanced	O
features	O
offered	O
by	O
more	O
robust	O
file	B-Protocol
transfer	I-Protocol
protocols	I-Protocol
.	O
</s>
<s>
TFTP	B-Device
only	O
reads	O
and	O
writes	O
files	O
from	O
or	O
to	O
a	O
remote	O
server	O
.	O
</s>
<s>
Today	O
TFTP	B-Device
is	O
generally	O
only	O
used	O
on	O
local	B-General_Concept
area	I-General_Concept
networks	I-General_Concept
(	O
LAN	B-General_Concept
)	O
.	O
</s>
<s>
In	O
TFTP	B-Device
,	O
a	O
transfer	O
is	O
initiated	O
by	O
the	O
client	B-Protocol
issuing	O
a	O
request	O
to	O
read	O
or	O
write	O
a	O
particular	O
file	O
on	O
the	O
server	O
.	O
</s>
<s>
The	O
request	O
can	O
optionally	O
include	O
a	O
set	O
of	O
negotiated	O
transfer	O
parameters	O
proposed	O
by	O
the	O
client	B-Protocol
under	O
the	O
terms	O
specified	O
by	O
RFC	O
2347	O
.	O
</s>
<s>
Each	O
block	O
of	O
transferred	O
data	O
,	O
which	O
is	O
usually	O
carried	O
within	O
a	O
single	O
IP	O
packet	B-Protocol
in	O
order	O
to	O
avoid	O
IP	O
fragmentation	O
,	O
must	O
be	O
acknowledged	O
by	O
an	O
acknowledgment	O
packet	B-Protocol
before	O
the	O
next	O
block	O
can	O
be	O
sent	O
.	O
</s>
<s>
A	O
data	B-Protocol
packet	I-Protocol
of	O
less	O
than	O
512	O
bytes	O
or	O
the	O
agreed	O
blocksize	O
option	O
signals	O
termination	O
of	O
a	O
transfer	O
.	O
</s>
<s>
If	O
a	O
packet	B-Protocol
gets	O
lost	O
in	O
the	O
network	O
,	O
the	O
intended	O
recipient	O
will	O
timeout	O
and	O
may	O
retransmit	O
their	O
last	O
packet	B-Protocol
(	O
which	O
may	O
be	O
data	O
or	O
an	O
acknowledgment	O
)	O
,	O
thus	O
causing	O
the	O
sender	O
of	O
the	O
lost	O
packet	B-Protocol
to	O
retransmit	O
that	O
lost	O
packet	B-Protocol
.	O
</s>
<s>
The	O
sender	O
has	O
to	O
keep	O
just	O
one	O
packet	B-Protocol
on	O
hand	O
for	O
retransmission	O
,	O
since	O
the	O
lock	O
step	O
acknowledgment	O
guarantees	O
that	O
all	O
older	O
packets	B-Protocol
have	O
been	O
correctly	O
received	O
.	O
</s>
<s>
TFTP	B-Device
defines	O
three	O
modes	O
of	O
transfer	O
:	O
netascii	O
,	O
octet	O
,	O
and	O
mail	O
.	O
</s>
<s>
Netascii	O
is	O
a	O
modified	O
form	O
of	O
ASCII	B-Protocol
,	O
defined	O
in	O
RFC	O
764	O
.	O
</s>
<s>
It	O
consists	O
of	O
an	O
8-bit	O
extension	O
of	O
the	O
7-bit	B-Protocol
ASCII	I-Protocol
character	O
space	O
from	O
0x20	O
to	O
0x7F	O
(	O
the	O
printable	O
characters	O
and	O
the	O
space	O
)	O
and	O
eight	O
of	O
the	O
control	O
characters	O
.	O
</s>
<s>
Netascii	O
also	O
requires	O
that	O
the	O
end	O
of	O
line	O
marker	O
on	O
a	O
host	B-Device
be	O
translated	O
to	O
the	O
character	O
pair	O
CR	O
LF	O
for	O
transmission	O
,	O
and	O
that	O
any	O
CR	O
must	O
be	O
followed	O
by	O
either	O
a	O
LF	O
or	O
the	O
null	O
.	O
</s>
<s>
More	O
correctly	O
,	O
if	O
a	O
host	B-Device
receives	O
an	O
octet	O
file	O
and	O
then	O
returns	O
it	O
,	O
the	O
returned	O
file	O
must	O
be	O
identical	O
to	O
the	O
original	O
.	O
</s>
<s>
TFTP	B-Device
uses	O
UDP	B-Protocol
as	O
its	O
transport	B-Architecture
protocol	I-Architecture
.	O
</s>
<s>
The	O
ports	O
are	O
chosen	O
at	O
random	O
according	O
to	O
the	O
parameters	O
of	O
the	O
networking	B-Protocol
stack	I-Protocol
,	O
typically	O
from	O
the	O
range	O
of	O
ephemeral	B-Protocol
ports	I-Protocol
.	O
</s>
<s>
The	O
initiating	O
host	B-Device
A	O
sends	O
an	O
RRQ	O
(	O
read	O
request	O
)	O
or	O
WRQ	O
(	O
write	O
request	O
)	O
packet	B-Protocol
to	O
host	B-Device
S	O
at	O
port	O
number	O
69	O
,	O
containing	O
the	O
filename	O
,	O
transfer	O
mode	O
,	O
and	O
optionally	O
any	O
negotiated	O
option	O
under	O
the	O
terms	O
of	O
RFC	O
2347	O
.	O
</s>
<s>
S	O
replies	O
with	O
an	O
option	O
ACK	O
if	O
options	O
were	O
used	O
,	O
and	O
an	O
ACK	O
(	O
acknowledgement	O
)	O
packet	B-Protocol
to	O
WRQ	O
and	O
directly	O
with	O
a	O
DATA	B-Protocol
packet	I-Protocol
to	O
RRQ	O
.	O
</s>
<s>
Packet	B-Protocol
is	O
sent	O
from	O
a	O
randomly	O
allocated	O
ephemeral	B-Protocol
port	I-Protocol
,	O
and	O
all	O
future	O
packets	B-Protocol
to	O
host	B-Device
S	O
should	O
be	O
directed	O
to	O
this	O
port	O
.	O
</s>
<s>
The	O
source	O
host	B-Device
sends	O
numbered	O
DATA	B-Protocol
packets	I-Protocol
to	O
the	O
destination	O
host	B-Device
,	O
all	O
but	O
the	O
last	O
containing	O
a	O
full-sized	O
block	O
of	O
data	O
(	O
512	O
bytes	O
default	O
)	O
.	O
</s>
<s>
The	O
destination	O
host	B-Device
replies	O
with	O
numbered	O
ACK	O
packets	B-Protocol
for	O
all	O
DATA	B-Protocol
packets	I-Protocol
.	O
</s>
<s>
The	O
final	O
DATA	B-Protocol
packet	I-Protocol
must	O
contain	O
less	O
than	O
a	O
full-sized	O
block	O
of	O
data	O
to	O
signal	O
that	O
it	O
is	O
the	O
last	O
.	O
</s>
<s>
If	O
the	O
size	O
of	O
the	O
transferred	O
file	O
is	O
an	O
exact	O
multiple	O
of	O
the	O
block-size	O
,	O
the	O
source	O
sends	O
a	O
final	O
DATA	B-Protocol
packet	I-Protocol
containing	O
0	O
bytes	O
of	O
data	O
.	O
</s>
<s>
If	O
an	O
ACK	O
is	O
not	O
eventually	O
received	O
,	O
a	O
retransmit	O
timer	O
re-sends	O
DATA	B-Protocol
packet	I-Protocol
.	O
</s>
<s>
TFTP	B-Device
has	O
always	O
been	O
associated	O
to	O
network	B-Device
booting	I-Device
.	O
</s>
<s>
One	O
of	O
the	O
first	O
attempts	O
in	O
this	O
regard	O
was	O
the	O
Bootstrap	O
Loading	O
using	O
TFTP	B-Device
standard	O
RFC	O
906	O
,	O
published	O
in	O
1984	O
,	O
which	O
established	O
the	O
1981	O
published	O
Trivial	B-Device
File	I-Device
Transfer	I-Device
Protocol	I-Device
standard	O
RFC	O
783	O
to	O
be	O
used	O
as	O
the	O
standard	O
file	B-Protocol
transfer	I-Protocol
protocol	I-Protocol
for	O
bootstrap	O
loading	O
.	O
</s>
<s>
It	O
was	O
followed	O
shortly	O
after	O
by	O
the	O
Bootstrap	B-Device
Protocol	I-Device
standard	O
RFC	O
951	O
(	O
BOOTP	B-Device
)	O
,	O
published	O
in	O
1985	O
,	O
which	O
allowed	O
a	O
disk-less	O
client	B-Protocol
machine	I-Protocol
to	O
discover	O
its	O
own	O
IP	O
address	O
,	O
the	O
address	O
of	O
a	O
TFTP	B-Device
server	O
,	O
and	O
the	O
name	O
of	O
a	O
Network	O
Bootstrap	O
Program	O
(	O
NBP	O
)	O
to	O
be	O
TFTP	B-Device
transferred	O
,	O
loaded	O
into	O
memory	O
,	O
and	O
executed	O
.	O
</s>
<s>
Dynamic	B-Protocol
Host	I-Protocol
Configuration	I-Protocol
Protocol	I-Protocol
standard	O
RFC	O
2131	O
(	O
DHCP	B-Protocol
)	O
published	O
in	O
1997	O
improved	O
BOOTP	B-Device
capabilities	O
.	O
</s>
<s>
Finally	O
,	O
the	O
Preboot	B-Device
Execution	I-Device
Environment	I-Device
(	O
PXE	B-Device
)	O
version	O
2.0	O
was	O
released	O
in	O
December	O
1998	O
,	O
and	O
the	O
update	O
2.1	O
was	O
made	O
public	O
in	O
September	O
1999	O
counting	O
on	O
TFTP	B-Device
as	O
its	O
file	B-Protocol
transfer	I-Protocol
protocol	I-Protocol
.	O
</s>
<s>
Intel	O
has	O
recently	O
decided	O
to	O
widely	O
support	O
PXE	B-Device
within	O
the	O
new	O
UEFI	B-Architecture
specification	O
extending	O
the	O
TFTP	B-Device
support	O
to	O
all	O
EFI/UEFI	O
environments	O
.	O
</s>
<s>
In	O
1998	O
this	O
limit	O
was	O
extended	O
to	O
65535	O
bytes/block	O
x	O
65535	O
blocks	O
=	O
4GB	O
by	O
TFTP	B-Device
Blocksize	O
Option	O
RFC	O
2348	O
.	O
</s>
<s>
If	O
the	O
defined	O
blocksize	O
produces	O
an	O
IP	O
packet	B-Protocol
size	O
that	O
exceeds	O
the	O
minimum	O
MTU	B-Protocol
at	O
any	O
point	O
of	O
the	O
network	O
path	O
,	O
IP	O
fragmentation	O
and	O
reassembly	O
will	O
occur	O
not	O
only	O
adding	O
more	O
overhead	O
but	O
also	O
leading	O
to	O
total	O
transfer	O
failure	O
when	O
the	O
minimalist	O
IP	B-Protocol
stack	I-Protocol
implementation	O
in	O
a	O
host	B-Device
's	O
BOOTP	B-Device
or	O
PXE	B-Device
ROM	O
does	O
not	O
(	O
or	O
fails	O
to	O
properly	O
)	O
implement	O
IP	O
fragmentation	O
and	O
reassembly	O
.	O
</s>
<s>
If	O
TFTP	B-Device
packets	B-Protocol
should	O
be	O
kept	O
within	O
the	O
standard	O
Ethernet	O
MTU	B-Protocol
(	O
1500	O
)	O
,	O
the	O
blocksize	O
value	O
is	O
calculated	O
as	O
1500	O
minus	O
headers	O
of	O
TFTP	B-Device
(	O
4	O
bytes	O
)	O
,	O
UDP	B-Protocol
(	O
8	O
bytes	O
)	O
and	O
IP	O
(	O
20	O
bytes	O
)	O
=	O
1468	O
bytes/block	O
,	O
this	O
gives	O
a	O
limit	O
of	O
1468	O
bytes/block	O
x	O
65535	O
blocks	O
=	O
92MB	O
.	O
</s>
<s>
Since	O
TFTP	B-Device
utilizes	O
UDP	B-Protocol
,	O
it	O
has	O
to	O
supply	O
its	O
own	O
transport	O
and	O
session	O
support	O
.	O
</s>
<s>
Each	O
file	O
transferred	O
via	O
TFTP	B-Device
constitutes	O
an	O
independent	O
exchange	O
.	O
</s>
<s>
Classically	O
,	O
this	O
transfer	O
is	O
performed	O
in	O
lock-step	O
,	O
with	O
only	O
one	O
packet	B-Protocol
(	O
either	O
a	O
block	O
of	O
data	O
,	O
or	O
an	O
'	O
acknowledgement	O
 '	O
)	O
alternatively	O
in	O
flight	O
on	O
the	O
network	O
at	O
any	O
time	O
.	O
</s>
<s>
Due	O
to	O
this	O
single	O
data	O
block	O
strategy	O
instead	O
of	O
sending	O
a	O
larger	O
amount	O
of	O
uninterrupted	O
data	O
blocks	O
before	O
pausing	O
the	O
transfer	O
to	O
wait	O
for	O
the	O
corresponding	O
acknowledge	O
(	O
windowing	O
)	O
,	O
TFTP	B-Device
provides	O
low	O
throughput	O
especially	O
over	O
high	O
latency	O
links	O
.	O
</s>
<s>
Microsoft	O
introduced	O
windowed	O
TFTP	B-Device
in	O
Windows	O
2008	O
as	O
part	O
of	O
their	O
Windows	O
Deployment	O
Services	O
(	O
WDS	O
)	O
,	O
in	O
January	O
2015	O
TFTP	B-Device
Windowsize	O
Option	O
RFC	O
7440	O
was	O
published	O
.	O
</s>
<s>
TFTP	B-Device
includes	O
no	O
login	O
or	O
access	O
control	O
mechanisms	O
.	O
</s>
<s>
Care	O
must	O
be	O
taken	O
when	O
using	O
TFTP	B-Device
for	O
file	O
transfers	O
where	O
authentication	O
,	O
access	O
control	O
,	O
confidentiality	O
,	O
or	O
integrity	O
checking	O
are	O
needed	O
.	O
</s>
<s>
Note	O
that	O
those	O
security	O
services	O
could	O
be	O
supplied	O
above	O
or	O
below	O
the	O
layer	O
at	O
which	O
TFTP	B-Device
runs	O
.	O
</s>
<s>
Care	O
must	O
also	O
be	O
taken	O
in	O
the	O
rights	O
granted	O
to	O
a	O
TFTP	B-Device
server	O
process	O
so	O
as	O
not	O
to	O
violate	O
the	O
security	O
of	O
the	O
server	O
's	O
file	O
system	O
.	O
</s>
<s>
TFTP	B-Device
is	O
often	O
installed	O
with	O
controls	O
such	O
that	O
only	O
files	O
that	O
have	O
public	O
read	O
access	O
are	O
available	O
via	O
TFTP	B-Device
.	O
</s>
<s>
Also	O
listing	O
,	O
deleting	O
,	O
renaming	O
,	O
and	O
writing	O
files	O
via	O
TFTP	B-Device
are	O
typically	O
disallowed	O
.	O
</s>
<s>
TFTP	B-Device
file	O
transfers	O
are	O
not	O
recommended	O
where	O
the	O
inherent	O
protocol	O
limitations	O
could	O
raise	O
insurmountable	O
liability	O
concerns	O
.	O
</s>
<s>
RFC	O
Number	O
Title	O
Published	O
Author	O
Obsolete	O
and	O
Update	O
InformationThe	O
TFTP	B-Device
Protocol	O
(	O
Revision	O
1	O
)	O
June	O
1981K	O
.	O
</s>
<s>
Sollins	O
Bootstrap	O
Loading	O
using	O
TFTPJune	O
1984Ross	O
Finlayson	O
Bootstrap	O
ProtocolSep.1985Bill	O
CroftUpdated	O
by	O
The	O
TFTP	B-Device
Protocol	O
(	O
Revision	O
2	O
)	O
July	O
1992K	O
.	O
</s>
<s>
SollinsUpdated	O
by	O
TFTP	B-Device
Option	O
ExtensionMarch	O
1995G	O
.	O
</s>
<s>
Malkin	O
Dynamic	O
Host	B-Device
Configuration	O
ProtocolMarch	O
1997R	O
.	O
</s>
<s>
DromsUpdated	O
by	O
TFTP	B-Device
Option	O
ExtensionMay	O
1998G	O
.	O
</s>
<s>
Malkin	O
TFTP	B-Device
Blocksize	O
OptionMay	O
1998G	O
.	O
</s>
<s>
Malkin	O
TFTP	B-Device
Timeout	O
Interval	O
and	O
Transfer	O
Size	O
OptionsMay	O
1998G	O
.	O
</s>
<s>
Malkin	O
Principles	O
of	O
Internet	B-Device
Host	I-Device
ConfigurationMay	O
2009B	O
.	O
</s>
<s>
Aboba	O
TFTP	B-Device
Windowsize	O
OptionJan	O
2015P	O
.	O
</s>
