<s>
In	O
computer	B-Architecture
networking	I-Architecture
,	O
the	O
maximum	B-Protocol
transmission	I-Protocol
unit	I-Protocol
(	O
MTU	B-Protocol
)	O
is	O
the	O
size	O
of	O
the	O
largest	O
protocol	B-Protocol
data	I-Protocol
unit	I-Protocol
(	O
PDU	O
)	O
that	O
can	O
be	O
communicated	O
in	O
a	O
single	O
network	B-Application
layer	I-Application
transaction	O
.	O
</s>
<s>
The	O
MTU	B-Protocol
relates	O
to	O
,	O
but	O
is	O
not	O
identical	O
to	O
the	O
maximum	O
frame	B-Protocol
size	O
that	O
can	O
be	O
transported	O
on	O
the	O
data	B-Protocol
link	I-Protocol
layer	I-Protocol
,	O
e.g.	O
</s>
<s>
Ethernet	B-Protocol
frame	I-Protocol
.	O
</s>
<s>
Larger	O
MTU	B-Protocol
is	O
associated	O
with	O
reduced	O
overhead	O
.	O
</s>
<s>
Smaller	O
MTU	B-Protocol
values	O
can	O
reduce	O
network	B-Protocol
delay	I-Protocol
.	O
</s>
<s>
In	O
many	O
cases	O
,	O
MTU	B-Protocol
is	O
dependent	O
on	O
underlying	O
network	O
capabilities	O
and	O
must	O
be	O
adjusted	O
manually	O
or	O
automatically	O
so	O
as	O
to	O
not	O
exceed	O
these	O
capabilities	O
.	O
</s>
<s>
MTU	B-Protocol
parameters	O
may	O
appear	O
in	O
association	O
with	O
a	O
communications	O
interface	O
or	O
standard	O
.	O
</s>
<s>
Some	O
systems	O
may	O
decide	O
MTU	B-Protocol
at	O
connect	O
time	O
,	O
e.g.	O
</s>
<s>
using	O
Path	B-Protocol
MTU	I-Protocol
Discovery	I-Protocol
.	O
</s>
<s>
MTUs	B-Protocol
apply	O
to	O
communications	O
protocols	O
and	O
network	B-Application
layers	I-Application
.	O
</s>
<s>
The	O
MTU	B-Protocol
is	O
specified	O
in	O
terms	O
of	O
bytes	B-Application
or	O
octets	O
of	O
the	O
largest	O
PDU	O
that	O
the	O
layer	O
can	O
pass	O
onwards	O
.	O
</s>
<s>
MTU	B-Protocol
parameters	O
usually	O
appear	O
in	O
association	O
with	O
a	O
communications	O
interface	O
(	O
NIC	B-Protocol
,	O
serial	B-Protocol
port	I-Protocol
,	O
etc	O
.	O
)	O
.	O
</s>
<s>
Standards	O
(	O
Ethernet	O
,	O
for	O
example	O
)	O
can	O
fix	O
the	O
size	O
of	O
an	O
MTU	B-Protocol
;	O
or	O
systems	O
(	O
such	O
as	O
point-to-point	O
serial	O
links	O
)	O
may	O
decide	O
MTU	B-Protocol
at	O
connect	O
time	O
.	O
</s>
<s>
Underlying	O
data	B-Protocol
link	I-Protocol
and	O
physical	B-Application
layers	I-Application
usually	O
add	O
overhead	O
to	O
the	O
network	B-Application
layer	I-Application
data	O
to	O
be	O
transported	O
,	O
so	O
for	O
a	O
given	O
maximum	O
frame	B-Protocol
size	O
of	O
a	O
medium	O
,	O
one	O
needs	O
to	O
subtract	O
the	O
amount	O
of	O
overhead	O
to	O
calculate	O
that	O
medium	O
's	O
MTU	B-Protocol
.	O
</s>
<s>
For	O
example	O
,	O
with	O
Ethernet	O
,	O
the	O
maximum	O
frame	B-Protocol
size	O
is	O
1518	O
bytes	B-Application
,	O
18	O
bytes	B-Application
of	O
which	O
are	O
overhead	O
(	O
header	O
and	O
frame	B-Protocol
check	I-Protocol
sequence	I-Protocol
)	O
,	O
resulting	O
in	O
an	O
MTU	B-Protocol
of	O
1500	O
bytes	B-Application
.	O
</s>
<s>
A	O
larger	O
MTU	B-Protocol
brings	O
greater	O
efficiency	O
because	O
each	O
network	B-Protocol
packet	I-Protocol
carries	O
more	O
user	O
data	O
while	O
protocol	O
overheads	O
,	O
such	O
as	O
headers	O
or	O
underlying	O
per-packet	O
delays	O
,	O
remain	O
fixed	O
;	O
the	O
resulting	O
higher	O
efficiency	O
means	O
an	O
improvement	O
in	O
bulk	O
protocol	O
throughput	O
.	O
</s>
<s>
A	O
larger	O
MTU	B-Protocol
also	O
requires	O
processing	O
of	O
fewer	O
packets	B-Protocol
for	O
the	O
same	O
amount	O
of	O
data	O
.	O
</s>
<s>
In	O
some	O
systems	O
,	O
per-packet-processing	O
can	O
be	O
a	O
critical	O
performance	O
limitation	O
.	O
</s>
<s>
Large	O
packets	B-Protocol
occupy	O
a	O
slow	O
link	O
for	O
more	O
time	O
than	O
a	O
smaller	O
packet	B-Protocol
,	O
causing	O
greater	O
delays	O
to	O
subsequent	O
packets	B-Protocol
,	O
and	O
increasing	O
network	B-Protocol
delay	I-Protocol
and	O
delay	B-Architecture
variation	I-Architecture
.	O
</s>
<s>
For	O
example	O
,	O
a	O
1500-byte	O
packet	B-Protocol
,	O
the	O
largest	O
allowed	O
by	O
Ethernet	O
at	O
the	O
network	B-Application
layer	I-Application
,	O
ties	O
up	O
a	O
14.4k	O
modem	O
for	O
about	O
one	O
second	O
.	O
</s>
<s>
Large	O
packets	B-Protocol
are	O
also	O
problematic	O
in	O
the	O
presence	O
of	O
communications	O
errors	O
.	O
</s>
<s>
If	O
no	O
forward	B-Error_Name
error	I-Error_Name
correction	I-Error_Name
is	O
used	O
,	O
corruption	O
of	O
a	O
single	O
bit	O
in	O
a	O
packet	B-Protocol
requires	O
that	O
the	O
entire	O
packet	B-Protocol
be	O
retransmitted	O
,	O
which	O
can	O
be	O
costly	O
.	O
</s>
<s>
At	O
a	O
given	O
bit	O
error	O
rate	O
,	O
larger	O
packets	B-Protocol
are	O
more	O
susceptible	O
to	O
corruption	O
.	O
</s>
<s>
Their	O
greater	O
payload	O
makes	O
retransmissions	O
of	O
larger	O
packets	B-Protocol
take	O
longer	O
.	O
</s>
<s>
Despite	O
the	O
negative	O
effects	O
on	O
retransmission	O
duration	O
,	O
large	O
packets	B-Protocol
can	O
still	O
have	O
a	O
net	O
positive	O
effect	O
on	O
end-to-end	O
TCP	B-Protocol
performance	O
.	O
</s>
<s>
The	O
Internet	B-Protocol
protocol	I-Protocol
suite	I-Protocol
was	O
designed	O
to	O
work	O
over	O
many	O
different	O
networking	O
technologies	O
,	O
each	O
of	O
which	O
may	O
use	O
packets	B-Protocol
of	O
different	O
sizes	O
.	O
</s>
<s>
While	O
a	O
host	O
will	O
know	O
the	O
MTU	B-Protocol
of	O
its	O
own	O
interface	O
and	O
possibly	O
that	O
of	O
its	O
peers	O
(	O
from	O
initial	O
handshakes	O
)	O
,	O
it	O
will	O
not	O
initially	O
know	O
the	O
lowest	O
MTU	B-Protocol
in	O
a	O
chain	O
of	O
links	O
to	O
other	O
peers	O
.	O
</s>
<s>
Another	O
potential	O
problem	O
is	O
that	O
higher-level	O
protocols	O
may	O
create	O
packets	B-Protocol
larger	O
than	O
even	O
the	O
local	O
link	O
supports	O
.	O
</s>
<s>
IPv4	B-Protocol
allows	O
fragmentation	B-Protocol
which	O
divides	O
the	O
datagram	B-Protocol
into	O
pieces	O
,	O
each	O
small	O
enough	O
to	O
accommodate	O
a	O
specified	O
MTU	B-Protocol
limitation	O
.	O
</s>
<s>
This	O
fragmentation	B-Protocol
process	O
takes	O
place	O
at	O
the	O
internet	B-Protocol
layer	I-Protocol
.	O
</s>
<s>
The	O
fragmented	O
packets	B-Protocol
are	O
marked	O
so	O
that	O
the	O
IP	O
layer	O
of	O
the	O
destination	O
host	O
knows	O
it	O
should	O
reassemble	O
the	O
packets	B-Protocol
into	O
the	O
original	O
datagram	B-Protocol
.	O
</s>
<s>
All	O
fragments	O
of	O
a	O
packet	B-Protocol
must	O
arrive	O
for	O
the	O
packet	B-Protocol
to	O
be	O
considered	O
received	O
.	O
</s>
<s>
If	O
the	O
network	O
drops	O
any	O
fragment	O
,	O
the	O
entire	O
packet	B-Protocol
is	O
lost	O
.	O
</s>
<s>
When	O
the	O
number	O
of	O
packets	B-Protocol
that	O
must	O
be	O
fragmented	O
or	O
the	O
number	O
of	O
fragments	O
is	O
great	O
,	O
fragmentation	B-Protocol
can	O
cause	O
unreasonable	O
or	O
unnecessary	O
overhead	O
.	O
</s>
<s>
For	O
example	O
,	O
various	O
tunneling	O
situations	O
may	O
exceed	O
the	O
MTU	B-Protocol
by	O
very	O
little	O
as	O
they	O
add	O
just	O
a	O
header	O
's	O
worth	O
of	O
data	O
.	O
</s>
<s>
The	O
addition	O
is	O
small	O
,	O
but	O
each	O
packet	B-Protocol
now	O
has	O
to	O
be	O
sent	O
in	O
two	O
fragments	O
,	O
the	O
second	O
of	O
which	O
carries	O
very	O
little	O
payload	O
.	O
</s>
<s>
The	O
same	O
amount	O
of	O
payload	O
is	O
being	O
moved	O
,	O
but	O
every	O
intermediate	O
router	O
has	O
to	O
forward	O
twice	O
as	O
many	O
packets	B-Protocol
.	O
</s>
<s>
The	O
Internet	B-Protocol
Protocol	I-Protocol
requires	O
that	O
hosts	O
must	O
be	O
able	O
to	O
process	O
IP	O
datagrams	B-Protocol
of	O
at	O
least	O
576	O
bytes	B-Application
(	O
for	O
IPv4	B-Protocol
)	O
or	O
1280	O
bytes	B-Application
(	O
for	O
IPv6	B-Protocol
)	O
.	O
</s>
<s>
However	O
,	O
this	O
does	O
not	O
preclude	O
link	B-Protocol
layers	I-Protocol
with	O
an	O
MTU	B-Protocol
smaller	O
than	O
this	O
minimum	O
MTU	B-Protocol
from	O
conveying	O
IP	O
data	O
.	O
</s>
<s>
For	O
example	O
,	O
according	O
to	O
IPv6	B-Protocol
's	O
specification	O
,	O
if	O
a	O
particular	O
link	B-Protocol
layer	I-Protocol
cannot	O
deliver	O
an	O
IP	O
datagram	B-Protocol
of	O
1280	O
bytes	B-Application
in	O
a	O
single	O
frame	B-Protocol
,	O
then	O
the	O
link	B-Protocol
layer	I-Protocol
must	O
provide	O
its	O
own	O
fragmentation	B-Protocol
and	O
reassembly	O
mechanism	O
,	O
separate	O
from	O
the	O
IP	B-Protocol
fragmentation	I-Protocol
mechanism	O
,	O
to	O
ensure	O
that	O
a	O
1280-byte	O
IP	O
datagram	B-Protocol
can	O
be	O
delivered	O
,	O
intact	O
,	O
to	O
the	O
IP	O
layer	O
.	O
</s>
<s>
In	O
the	O
context	O
of	O
Internet	B-Protocol
Protocol	I-Protocol
,	O
MTU	B-Protocol
refers	O
to	O
the	O
maximum	O
size	O
of	O
an	O
IP	O
packet	B-Protocol
that	O
can	O
be	O
transmitted	O
without	O
fragmentation	B-Protocol
over	O
a	O
given	O
medium	O
.	O
</s>
<s>
The	O
size	O
of	O
an	O
IP	O
packet	B-Protocol
includes	O
IP	O
headers	O
but	O
excludes	O
headers	O
from	O
the	O
link	B-Protocol
layer	I-Protocol
.	O
</s>
<s>
In	O
the	O
case	O
of	O
an	O
Ethernet	B-Protocol
frame	I-Protocol
this	O
adds	O
an	O
overhead	O
of	O
18	O
bytes	B-Application
,	O
or	O
22	O
bytes	B-Application
with	O
an	O
IEEE	O
802.1Q	O
tag	O
for	O
VLAN	O
tagging	O
or	O
class	B-Device
of	I-Device
service	I-Device
.	O
</s>
<s>
The	O
MTU	B-Protocol
should	O
not	O
be	O
confused	O
with	O
the	O
minimum	O
datagram	B-Protocol
size	O
that	O
all	O
hosts	O
must	O
be	O
prepared	O
to	O
accept	O
.	O
</s>
<s>
This	O
is	O
576	O
bytes	B-Application
for	O
IPv4	B-Protocol
and	O
of	O
1280	O
bytes	B-Application
for	O
IPv6	B-Protocol
.	O
</s>
<s>
Media	O
for	O
IP	O
transport	O
Maximum	B-Protocol
transmission	I-Protocol
unit	I-Protocol
(	O
bytes	B-Application
)	O
Notes	O
Internet	O
IPv4	B-Protocol
path	B-Protocol
MTU	I-Protocol
At	O
least	O
68	O
,	O
max	O
of	O
64	O
KiB	O
Systems	O
may	O
use	O
Path	B-Protocol
MTU	I-Protocol
Discovery	I-Protocol
to	O
find	O
the	O
actual	O
path	B-Protocol
MTU	I-Protocol
.	O
</s>
<s>
Routing	O
from	O
larger	O
MTU	B-Protocol
to	O
smaller	O
MTU	B-Protocol
causes	O
IP	B-Protocol
fragmentation	I-Protocol
.	O
</s>
<s>
Internet	O
IPv6	B-Protocol
path	B-Protocol
MTU	I-Protocol
At	O
least	O
1280	O
,	O
max	O
of	O
64	O
KiB	O
,	O
but	O
up	O
to	O
4	O
GiB	O
with	O
optional	O
jumbogram	B-Protocol
,	O
p	O
.	O
1	O
,	O
"	O
The	O
IPv6	B-Protocol
header	O
 [ IPv6 ] 	O
has	O
a	O
16-bit	O
Payload	O
Length	O
field	O
and	O
,	O
therefore	O
,	O
supports	O
payloads	O
up	O
to	O
65,535	O
octets	O
long	O
.	O
</s>
<s>
This	O
document	O
specifies	O
an	O
IPv6	B-Protocol
hop-by-hop	O
option	O
,	O
called	O
the	O
Jumbo	B-Protocol
Payload	I-Protocol
option	O
,	O
that	O
carries	O
a	O
32-bit	O
length	O
field	O
in	O
order	O
to	O
allow	O
transmission	O
of	O
IPv6	B-Protocol
packets	B-Protocol
with	O
payloads	O
between	O
65,536	O
and	O
4,294,967,295	O
octets	O
in	O
length	O
.	O
</s>
<s>
Packets	B-Protocol
with	O
such	O
long	O
payloads	O
are	O
referred	O
to	O
as	O
'	O
jumbograms	B-Protocol
 '	O
.	O
"	O
</s>
<s>
Systems	O
must	O
use	O
Path	B-Protocol
MTU	I-Protocol
Discovery	I-Protocol
to	O
find	O
the	O
actual	O
path	B-Protocol
MTU	I-Protocol
.	O
</s>
<s>
X.25	B-Protocol
Minimal	O
576	O
(	O
sending	O
)	O
or	O
1600	O
(	O
receiving	O
)	O
Ethernet	B-Protocol
v2	I-Protocol
1500	O
Network	O
Working	O
Group	O
of	O
the	O
IETF	O
,	O
</s>
<s>
:	O
A	O
Standard	O
for	O
the	O
Transmission	O
of	O
IP	O
Datagrams	B-Protocol
over	O
Ethernet	O
Networks	O
,	O
</s>
<s>
"	O
The	O
maximum	O
length	O
of	O
the	O
data	O
field	O
of	O
a	O
packet	B-Protocol
sent	O
over	O
an	O
Ethernet	O
is	O
1500	O
octets	O
,	O
thus	O
the	O
maximum	O
length	O
of	O
an	O
IP	O
datagram	B-Protocol
sent	O
over	O
an	O
Ethernet	O
is	O
1500	O
octets	O
.	O
</s>
<s>
ERRATA	O
Nearly	O
all	O
IP	O
over	O
Ethernet	O
implementations	O
use	O
the	O
Ethernet	O
II	O
frame	B-Protocol
format	O
.	O
</s>
<s>
Ethernet	O
with	O
LLC	O
and	O
SNAP	B-Protocol
1492IEEE	O
802.3	O
Ethernet	O
jumbo	B-Protocol
frames	I-Protocol
1501	O
–	O
9202	O
or	O
more	O
The	O
limit	O
varies	O
by	O
vendor	O
.	O
</s>
<s>
For	O
correct	O
interoperation	O
,	O
frames	O
should	O
be	O
no	O
larger	O
than	O
the	O
maximum	O
frame	B-Protocol
size	O
supported	O
by	O
any	O
device	O
on	O
the	O
network	B-Protocol
segment	I-Protocol
.	O
</s>
<s>
Jumbo	B-Protocol
frames	I-Protocol
are	O
usually	O
only	O
seen	O
in	O
special-purpose	O
networks	O
.	O
</s>
<s>
PPPoE	B-Protocol
v2	I-Protocol
1492	O
with	O
the	O
standard	O
Ethernet	O
MTU	B-Protocol
of	O
1500	O
bytes	B-Application
;	O
extensions	O
exist	O
Ethernet	O
II	O
MTU	B-Protocol
(	O
1500	O
)	O
less	O
PPPoE	B-Protocol
header	O
(	O
8	O
)	O
DS-Lite	O
over	O
PPPoE	B-Protocol
1452	O
Ethernet	O
II	O
MTU	B-Protocol
(	O
1500	O
)	O
less	O
PPPoE	B-Protocol
header	O
(	O
8	O
)	O
and	O
IPv6	B-Protocol
header	O
(	O
40	O
)	O
PPPoE	B-Protocol
jumbo	B-Protocol
frames	I-Protocol
1493	O
–	O
9190	O
or	O
more	O
Ethernet	O
Jumbo	B-Protocol
Frame	I-Protocol
MTU	B-Protocol
(	O
1501	O
-	O
9198	O
)	O
less	O
PPPoE	B-Protocol
header	O
(	O
8	O
)	O
IEEE	O
802.11	O
Wi-Fi	O
(	O
WLAN	O
)	O
2304802.11-2012	O
,	O
page	O
413	O
,	O
section	O
8.3.2.1The	O
maximum	O
MSDU	O
size	O
is	O
2304	O
before	O
encryption	O
.	O
</s>
<s>
WEP	O
will	O
add	O
8	O
bytes	B-Application
,	O
WPA-TKIP	O
20	O
bytes	B-Application
,	O
and	O
WPA2-CCMP	O
16	O
bytes	B-Application
.	O
</s>
<s>
The	O
IP	O
MTU	B-Protocol
and	O
Ethernet	O
maximum	O
frame	B-Protocol
size	O
are	O
configured	O
separately	O
.	O
</s>
<s>
In	O
Ethernet	B-Protocol
switch	I-Protocol
configuration	O
,	O
MTU	B-Protocol
may	O
refer	O
to	O
Ethernet	O
maximum	O
frame	B-Protocol
size	O
.	O
</s>
<s>
In	O
Ethernet-based	O
routers	O
,	O
MTU	B-Protocol
normally	O
refers	O
to	O
the	O
IP	O
MTU	B-Protocol
.	O
</s>
<s>
If	O
jumbo	B-Protocol
frames	I-Protocol
are	O
allowed	O
in	O
a	O
network	O
,	O
the	O
IP	O
MTU	B-Protocol
should	O
also	O
be	O
adjusted	O
upwards	O
to	O
take	O
advantage	O
of	O
this	O
.	O
</s>
<s>
Since	O
the	O
IP	O
packet	B-Protocol
is	O
carried	O
by	O
an	O
Ethernet	B-Protocol
frame	I-Protocol
,	O
the	O
Ethernet	B-Protocol
frame	I-Protocol
has	O
to	O
be	O
larger	O
than	O
the	O
IP	O
packet	B-Protocol
.	O
</s>
<s>
With	O
the	O
normal	O
untagged	O
Ethernet	B-Protocol
frame	I-Protocol
overhead	O
of	O
18	O
bytes	B-Application
,	O
the	O
Ethernet	O
maximum	O
frame	B-Protocol
size	O
is	O
1518	O
bytes	B-Application
.	O
</s>
<s>
If	O
a	O
1500	O
byte	B-Application
IP	O
packet	B-Protocol
is	O
to	O
be	O
carried	O
over	O
a	O
tagged	O
Ethernet	O
connection	O
,	O
the	O
Ethernet	B-Protocol
frame	I-Protocol
maximum	O
size	O
needs	O
to	O
be	O
1522	O
due	O
to	O
the	O
larger	O
size	O
of	O
an	O
802.1Q	O
tagged	O
frame	B-Protocol
.	O
</s>
<s>
802.3ac	O
increases	O
the	O
standard	O
Ethernet	O
maximum	O
frame	B-Protocol
size	O
to	O
accommodate	O
this	O
.	O
</s>
<s>
The	O
Internet	B-Protocol
Protocol	I-Protocol
defines	O
the	O
path	B-Protocol
MTU	I-Protocol
of	O
an	O
Internet	O
transmission	O
path	O
as	O
the	O
smallest	O
MTU	B-Protocol
supported	O
by	O
any	O
of	O
the	O
hops	O
on	O
the	O
path	O
between	O
a	O
source	O
and	O
destination	O
.	O
</s>
<s>
Put	O
another	O
way	O
,	O
the	O
path	B-Protocol
MTU	I-Protocol
is	O
the	O
largest	O
packet	B-Protocol
size	O
that	O
can	O
traverse	O
this	O
path	O
without	O
suffering	O
fragmentation	B-Protocol
.	O
</s>
<s>
Path	B-Protocol
MTU	I-Protocol
Discovery	I-Protocol
is	O
a	O
technique	O
for	O
determining	O
the	O
path	B-Protocol
MTU	I-Protocol
between	O
two	O
IP	O
hosts	O
,	O
defined	O
for	O
both	O
IPv4	B-Protocol
and	O
IPv6	B-Protocol
.	O
</s>
<s>
It	O
works	O
by	O
sending	O
packets	B-Protocol
with	O
the	O
DF	O
(	O
do	O
n't	O
fragment	O
)	O
option	O
in	O
the	O
IP	O
header	O
set	O
.	O
</s>
<s>
Any	O
device	O
along	O
the	O
path	O
whose	O
MTU	B-Protocol
is	O
smaller	O
than	O
the	O
packet	B-Protocol
will	O
drop	O
such	O
packets	B-Protocol
and	O
send	O
back	O
an	O
ICMP	O
Destination	O
Unreachable	O
(	O
Datagram	B-Protocol
Too	O
Big	O
)	O
message	O
which	O
indicates	O
its	O
MTU	B-Protocol
.	O
</s>
<s>
This	O
information	O
allows	O
the	O
source	O
host	O
to	O
reduce	O
its	O
assumed	O
path	B-Protocol
MTU	I-Protocol
appropriately	O
.	O
</s>
<s>
The	O
process	O
repeats	O
until	O
the	O
MTU	B-Protocol
becomes	O
small	O
enough	O
to	O
traverse	O
the	O
entire	O
path	O
without	O
fragmentation	B-Protocol
.	O
</s>
<s>
Standard	O
Ethernet	O
supports	O
an	O
MTU	B-Protocol
of	O
1500	O
bytes	B-Application
and	O
Ethernet	O
implementation	O
supporting	O
jumbo	B-Protocol
frames	I-Protocol
,	O
allow	O
for	O
an	O
MTU	B-Protocol
up	O
to	O
9000	O
bytes	B-Application
.	O
</s>
<s>
However	O
,	O
border	O
protocols	O
like	O
PPPoE	B-Protocol
will	O
reduce	O
this	O
.	O
</s>
<s>
Path	B-Protocol
MTU	I-Protocol
Discovery	I-Protocol
exposes	O
the	O
difference	O
between	O
the	O
MTU	B-Protocol
seen	O
by	O
Ethernet	O
end-nodes	O
and	O
the	O
Path	B-Protocol
MTU	I-Protocol
.	O
</s>
<s>
Unfortunately	O
,	O
increasing	O
numbers	O
of	O
networks	O
drop	B-Protocol
ICMP	I-Protocol
traffic	I-Protocol
(	O
for	O
example	O
,	O
to	O
prevent	O
denial-of-service	O
attacks	O
)	O
,	O
which	O
prevents	O
path	B-Protocol
MTU	I-Protocol
discovery	I-Protocol
from	O
working	O
.	O
</s>
<s>
Packetization	O
Layer	O
Path	B-Protocol
MTU	I-Protocol
Discovery	I-Protocol
is	O
a	O
Path	B-Protocol
MTU	I-Protocol
Discovery	I-Protocol
technique	O
which	O
responds	O
more	O
robustly	O
to	O
ICMP	O
filtering	O
.	O
</s>
<s>
In	O
an	O
IP	B-Protocol
network	I-Protocol
,	O
the	O
path	O
from	O
the	O
source	O
address	O
to	O
the	O
destination	O
address	O
may	O
change	O
in	O
response	O
to	O
various	O
events	O
(	O
load-balancing	B-Application
,	O
congestion	B-Protocol
,	O
outages	O
,	O
etc	O
.	O
)	O
</s>
<s>
and	O
this	O
could	O
result	O
in	O
the	O
path	B-Protocol
MTU	I-Protocol
changing	O
(	O
sometimes	O
repeatedly	O
)	O
during	O
a	O
transmission	O
,	O
which	O
may	O
introduce	O
further	O
packet	B-Protocol
drops	O
before	O
the	O
host	O
finds	O
a	O
new	O
reliable	O
MTU	B-Protocol
.	O
</s>
<s>
A	O
failure	O
of	O
Path	B-Protocol
MTU	I-Protocol
Discovery	I-Protocol
carries	O
the	O
possible	O
result	O
of	O
making	O
some	O
sites	O
behind	O
badly	O
configured	O
firewalls	B-Application
unreachable	O
.	O
</s>
<s>
A	O
connection	O
with	O
mismatched	O
MTU	B-Protocol
may	O
work	O
for	O
low-volume	O
data	O
but	O
fail	O
as	O
soon	O
as	O
a	O
host	O
sends	O
a	O
large	O
block	O
of	O
data	O
.	O
</s>
<s>
For	O
example	O
,	O
with	O
Internet	B-Protocol
Relay	I-Protocol
Chat	I-Protocol
a	O
connecting	O
client	O
might	O
see	O
the	O
initial	O
messages	O
up	O
to	O
and	O
including	O
the	O
initial	O
ping	B-Protocol
(	O
sent	O
by	O
the	O
server	O
as	O
an	O
anti-spoofing	O
measure	O
)	O
,	O
but	O
get	O
no	O
response	O
after	O
that	O
.	O
</s>
<s>
This	O
is	O
because	O
the	O
large	O
set	O
of	O
welcome	O
messages	O
sent	O
at	O
that	O
point	O
are	O
packets	B-Protocol
that	O
exceed	O
the	O
path	B-Protocol
MTU	I-Protocol
.	O
</s>
<s>
One	O
can	O
possibly	O
work	O
around	O
this	O
,	O
depending	O
on	O
which	O
part	O
of	O
the	O
network	O
one	O
controls	O
;	O
for	O
example	O
one	O
can	O
change	O
the	O
MSS	O
(	O
maximum	B-Protocol
segment	I-Protocol
size	I-Protocol
)	O
in	O
the	O
initial	O
packet	B-Protocol
that	O
sets	O
up	O
the	O
TCP	B-Protocol
connection	O
at	O
one	O
's	O
firewall	B-Application
.	O
</s>
<s>
MTU	B-Protocol
is	O
sometimes	O
used	O
to	O
describe	O
the	O
maximum	O
PDU	O
sizes	O
in	O
communication	O
layers	O
other	O
than	O
the	O
network	B-Application
layer	I-Application
.	O
</s>
<s>
Cisco	O
Systems	O
and	O
MikroTik	O
use	O
L2	O
MTU	B-Protocol
for	O
the	O
maximum	O
frame	B-Protocol
size	O
.	O
</s>
<s>
Dell/Force10	O
use	O
MTU	B-Protocol
for	O
the	O
maximum	O
frame	B-Protocol
size	O
.	O
</s>
<s>
Hewlett-Packard	O
used	O
just	O
MTU	B-Protocol
for	O
the	O
maximum	O
frame	B-Protocol
size	O
including	O
the	O
optional	O
IEEE	O
802.1Q	O
tag	O
.	O
</s>
<s>
Juniper	O
Networks	O
use	O
several	O
MTU	B-Protocol
terms	O
:	O
Physical	O
Interface	O
MTU	B-Protocol
(	O
L3	O
MTU	B-Protocol
plus	O
some	O
unspecified	O
protocol	O
overhead	O
)	O
,	O
Logical	O
Interface	O
MTU	B-Protocol
(	O
consistent	O
with	O
IETF	O
MTU	B-Protocol
)	O
and	O
Maximum	O
MTU	B-Protocol
(	O
maximum	O
configurable	O
frame	B-Protocol
size	O
for	O
jumbo	B-Protocol
frames	I-Protocol
)	O
.	O
</s>
<s>
The	O
transmission	O
of	O
a	O
packet	B-Protocol
on	O
a	O
physical	O
network	B-Protocol
segment	I-Protocol
that	O
is	O
larger	O
than	O
the	O
segment	O
's	O
MTU	B-Protocol
is	O
known	O
as	O
jabber	O
.	O
</s>
<s>
Network	B-Protocol
switches	I-Protocol
and	O
some	O
repeater	B-Protocol
hubs	I-Protocol
have	O
a	O
built-in	O
capability	O
to	O
detect	O
when	O
a	O
device	O
is	O
jabbering	O
.	O
</s>
