<s>
The	O
network	B-Protocol
interface	I-Protocol
layer	I-Protocol
,	O
also	O
commonly	O
referred	O
to	O
as	O
the	O
data	O
link	B-Protocol
layer	I-Protocol
or	O
link	B-Protocol
layer	I-Protocol
,	O
is	O
the	O
lowest	O
layer	O
in	O
the	O
TCP/IP	B-Protocol
model	I-Protocol
.	O
</s>
<s>
The	O
network	B-Protocol
interface	I-Protocol
layer	I-Protocol
,	O
commonly	O
referred	O
to	O
as	O
the	O
data	O
link	B-Protocol
layer	I-Protocol
,	O
is	O
the	O
physical	O
interface	O
between	O
the	O
host	O
system	O
and	O
the	O
network	O
hardware	O
.	O
</s>
<s>
Some	O
common	O
link	B-Protocol
layer	I-Protocol
protocols	O
include	O
IEEE	O
802.2	O
and	O
X.25	B-Protocol
.	O
</s>
<s>
The	O
data	O
link	B-Protocol
layer	I-Protocol
and	O
its	O
associated	O
protocols	O
govern	O
the	O
physical	O
interface	O
between	O
the	O
host	O
computer	O
and	O
the	O
network	O
hardware	O
.	O
</s>
<s>
Checksums	B-Algorithm
Sending	O
checksum	B-Algorithm
data	O
for	O
each	O
frame	O
to	O
enable	O
the	O
receiving	O
node	O
to	O
determine	O
whether	O
or	O
not	O
the	O
frame	O
was	O
received	O
error-free	O
.	O
</s>
<s>
The	O
data	O
link	B-Protocol
layer	I-Protocol
addresses	O
data	O
packets	O
based	O
on	O
the	O
destination	O
hardware	O
's	O
physical	O
Media	O
Access	O
Control	O
(	O
MAC	O
)	O
address	O
.	O
</s>
<s>
At	O
the	O
data	O
link	B-Protocol
layer	I-Protocol
a	O
logical	O
IP	B-Protocol
address	I-Protocol
assigned	O
by	O
the	O
network	O
layer	O
is	O
translated	O
into	O
a	O
physical	O
MAC	O
address	O
.	O
</s>
<s>
If	O
a	O
client	O
or	O
switch	O
is	O
unsure	O
of	O
the	O
IP-to-MAC	O
mapping	O
of	O
a	O
data	O
packet	O
it	O
receives	O
it	O
will	O
send	O
an	O
Address	O
Resolution	O
Protocol	O
(	O
ARP	O
)	O
message	O
to	O
the	O
nearest	O
switch	O
asking	O
for	O
the	O
MAC	O
address	O
associated	O
with	O
the	O
particular	O
IP	B-Protocol
address	I-Protocol
.	O
</s>
<s>
In	O
an	O
ARP	O
spoofing	O
attack	O
the	O
adversary	O
broadcasts	O
the	O
IP	B-Protocol
address	I-Protocol
of	O
the	O
machine	O
to	O
be	O
attacked	O
along	O
with	O
its	O
own	O
MAC	O
address	O
.	O
</s>
<s>
All	O
neighboring	O
switches	O
will	O
then	O
update	O
their	O
mapping	O
tables	O
and	O
begin	O
transmitting	O
data	O
destined	O
to	O
the	O
attacked	O
system	O
's	O
IP	B-Protocol
address	I-Protocol
to	O
the	O
attacker	O
's	O
MAC	O
address	O
.	O
</s>
<s>
These	O
techniques	O
may	O
be	O
integrated	O
with	O
the	O
Dynamic	B-Protocol
Host	I-Protocol
Configuration	I-Protocol
Protocol	I-Protocol
(	O
DHCP	B-Protocol
)	O
server	O
so	O
that	O
both	O
dynamic	O
and	O
static	O
IP	B-Protocol
addresses	I-Protocol
are	O
certified	O
.	O
</s>
<s>
When	O
a	O
client	O
system	O
without	O
an	O
IP	B-Protocol
address	I-Protocol
enters	O
a	O
network	O
it	O
will	O
request	O
an	O
IP	B-Protocol
address	I-Protocol
from	O
the	O
resident	O
DHCP	B-Protocol
server	I-Protocol
.	O
</s>
<s>
The	O
DHCP	B-Protocol
server	I-Protocol
will	O
reserve	O
an	O
IP	B-Protocol
address	I-Protocol
(	O
so	O
anyone	O
else	O
asking	O
for	O
one	O
is	O
not	O
granted	O
this	O
one	O
)	O
and	O
it	O
will	O
send	O
that	O
IP	B-Protocol
address	I-Protocol
to	O
the	O
device	O
along	O
with	O
a	O
lease	O
identifying	O
how	O
long	O
the	O
address	O
will	O
be	O
valid	O
.	O
</s>
<s>
Normally	O
,	O
from	O
this	O
point	O
,	O
the	O
device	O
will	O
respond	O
by	O
confirming	O
the	O
IP	B-Protocol
address	I-Protocol
with	O
the	O
DHCP	B-Protocol
server	I-Protocol
and	O
the	O
DHCP	B-Protocol
server	I-Protocol
finally	O
responds	O
with	O
an	O
acknowledgement	O
.	O
</s>
<s>
In	O
a	O
DHCP	B-Protocol
starvation	O
attack	O
,	O
once	O
the	O
adversary	O
receives	O
the	O
IP	B-Protocol
address	I-Protocol
and	O
the	O
lease	O
period	O
from	O
the	O
DHCP	B-Protocol
server	I-Protocol
,	O
the	O
adversary	O
does	O
not	O
respond	O
with	O
the	O
confirmation	O
.	O
</s>
<s>
Instead	O
,	O
the	O
adversary	O
floods	O
the	O
DHCP	B-Protocol
server	I-Protocol
with	O
IP	B-Protocol
address	I-Protocol
requests	O
until	O
all	O
addresses	O
within	O
the	O
server	O
's	O
address	O
space	O
have	O
been	O
reserved	O
(	O
exhausted	O
)	O
.	O
</s>
<s>
The	O
adversary	O
can	O
then	O
set	O
up	O
a	O
rogue	O
DHCP	B-Protocol
server	I-Protocol
so	O
that	O
clients	O
receive	O
incorrect	O
network	O
settings	O
and	O
as	O
a	O
result	O
transmit	O
data	O
to	O
an	O
attacker	O
's	O
machine	O
.	O
</s>
<s>
The	O
IP	O
guard	O
initially	O
blocks	O
all	O
traffic	O
except	O
DHCP	B-Protocol
packets	O
.	O
</s>
<s>
When	O
a	O
client	O
receives	O
a	O
valid	O
IP	B-Protocol
address	I-Protocol
from	O
the	O
DHCP	B-Protocol
server	I-Protocol
the	O
IP	B-Protocol
address	I-Protocol
and	O
switch	O
port	O
relationship	O
are	O
bound	O
in	O
an	O
Access	O
Control	O
List	O
(	O
ACL	O
)	O
.	O
</s>
<s>
The	O
ACL	O
then	O
restricts	O
traffic	O
only	O
to	O
those	O
IP	B-Protocol
addresses	I-Protocol
configured	O
in	O
the	O
binding	O
.	O
</s>
<s>
If	O
nodes	O
A	O
and	O
B	O
are	O
both	O
wireless	O
laptop	O
computers	O
communicating	O
in	O
an	O
office	O
environment	O
their	O
physical	O
separation	O
may	O
require	O
that	O
they	O
communicate	O
through	O
a	O
wireless	B-Device
access	I-Device
point	I-Device
.	O
</s>
<s>
An	O
attacker	O
can	O
send	O
deauth	O
messages	O
to	O
an	O
access	O
point	O
tied	O
to	O
client	O
IP	B-Protocol
addresses	I-Protocol
thereby	O
knocking	O
the	O
users	O
off-line	O
and	O
requiring	O
continued	O
re-authenticate	O
,	O
giving	O
the	O
attacker	O
valuable	O
insight	O
into	O
the	O
reauthentication	O
handshaking	O
that	O
occurs	O
.	O
</s>
