<s>
IP	B-Protocol
traceback	I-Protocol
is	O
any	O
method	O
for	O
reliably	O
determining	O
the	O
origin	O
of	O
a	O
packet	B-Protocol
on	O
the	O
Internet	O
.	O
</s>
<s>
The	O
IP	B-Protocol
protocol	I-Protocol
does	O
not	O
provide	O
for	O
the	O
authentication	O
of	O
the	O
source	O
IP	B-Protocol
address	I-Protocol
of	O
an	O
IP	B-Protocol
packet	B-Protocol
,	O
enabling	O
the	O
source	O
address	O
to	O
be	O
falsified	O
in	O
a	O
strategy	O
called	O
IP	B-Protocol
address	I-Protocol
spoofing	O
,	O
and	O
creating	O
potential	O
internet	O
security	O
and	O
stability	O
problems	O
.	O
</s>
<s>
Use	O
of	O
false	O
source	O
IP	B-Protocol
addresses	I-Protocol
allows	O
denial-of-service	O
attacks	O
(	O
DoS	O
)	O
or	O
one-way	O
attacks	O
(	O
where	O
the	O
response	O
from	O
the	O
victim	O
host	O
is	O
so	O
well	O
known	O
that	O
return	O
packets	B-Protocol
need	O
not	O
be	O
received	O
to	O
continue	O
the	O
attack	O
)	O
.	O
</s>
<s>
IP	B-Protocol
traceback	I-Protocol
is	O
critical	O
for	O
identifying	O
sources	O
of	O
attacks	O
and	O
instituting	O
protection	O
measures	O
for	O
the	O
Internet	O
.	O
</s>
<s>
Such	O
solutions	O
require	O
high	O
numbers	O
of	O
packets	B-Protocol
to	O
converge	O
on	O
the	O
attack	O
path(s )	O
.	O
</s>
<s>
suggested	O
probabilistically	O
marking	O
packets	B-Protocol
as	O
they	O
traverse	O
routers	O
through	O
the	O
Internet	O
.	O
</s>
<s>
They	O
propose	O
that	O
the	O
router	O
mark	O
the	O
packet	B-Protocol
with	O
either	O
the	O
router	O
’s	O
IP	B-Protocol
address	I-Protocol
or	O
the	O
edges	O
of	O
the	O
path	O
that	O
the	O
packet	B-Protocol
traversed	O
to	O
reach	O
the	O
router	O
.	O
</s>
<s>
For	O
the	O
first	O
alternative	O
,	O
marking	O
packets	B-Protocol
with	O
the	O
router	O
's	O
IP	B-Protocol
address	I-Protocol
,	O
analysis	O
shows	O
that	O
in	O
order	O
to	O
gain	O
the	O
correct	O
attack	O
path	O
with	O
95%	O
accuracy	O
as	O
many	O
as	O
294,000	O
packets	B-Protocol
are	O
required	O
.	O
</s>
<s>
The	O
second	O
approach	O
,	O
edge	O
marking	O
,	O
requires	O
that	O
the	O
two	O
nodes	O
that	O
make	O
up	O
an	O
edge	O
mark	O
the	O
path	O
with	O
their	O
IP	B-Protocol
addresses	I-Protocol
along	O
with	O
the	O
distance	O
between	O
them	O
.	O
</s>
<s>
This	O
approach	O
would	O
require	O
more	O
state	O
information	O
in	O
each	O
packet	B-Protocol
than	O
simple	O
node	O
marking	O
but	O
would	O
converge	O
much	O
faster	O
.	O
</s>
<s>
Node	O
a	O
inserts	O
its	O
IP	B-Protocol
address	I-Protocol
into	O
the	O
packet	B-Protocol
and	O
sends	O
it	O
to	O
b	O
.	O
</s>
<s>
When	O
enough	O
packets	B-Protocol
are	O
received	O
,	O
the	O
victim	O
can	O
reconstruct	O
all	O
of	O
the	O
edges	O
the	O
series	O
of	O
packets	B-Protocol
traversed	O
(	O
even	O
in	O
the	O
presence	O
of	O
multiple	O
attackers	O
)	O
.	O
</s>
<s>
Accordingly	O
,	O
Song	O
and	O
Perrig	O
propose	O
the	O
following	O
traceback	O
scheme	O
:	O
instead	O
of	O
encoding	O
the	O
IP	B-Protocol
address	I-Protocol
interleaved	O
with	O
a	O
hash	B-Error_Name
,	O
they	O
suggest	O
encoding	O
the	O
IP	B-Protocol
address	I-Protocol
into	O
an	O
11	O
bit	O
hash	B-Error_Name
and	O
maintain	O
a	O
5	O
bit	O
hop	O
count	O
,	O
both	O
stored	O
in	O
the	O
16-bit	O
fragment	O
ID	O
field	O
.	O
</s>
<s>
Further	O
,	O
they	O
suggest	O
that	O
two	O
different	O
hashing	B-Error_Name
functions	I-Error_Name
be	O
used	O
so	O
that	O
the	O
order	O
of	O
the	O
routers	O
in	O
the	O
markings	O
can	O
be	O
determined	O
.	O
</s>
<s>
If	O
this	O
is	O
the	O
case	O
,	O
it	O
generates	O
an	O
11-bit	O
hash	B-Error_Name
of	O
its	O
own	O
IP	B-Protocol
address	I-Protocol
and	O
then	O
XORs	O
it	O
with	O
the	O
previous	O
hop	O
.	O
</s>
<s>
If	O
it	O
finds	O
a	O
non-zero	O
hop	O
count	O
it	O
inserts	O
its	O
IP	B-Protocol
hash	B-Error_Name
,	O
sets	O
the	O
hop	O
count	O
to	O
zero	O
and	O
forwards	O
the	O
packet	B-Protocol
on	O
.	O
</s>
<s>
If	O
a	O
router	O
decides	O
not	O
to	O
mark	O
the	O
packet	B-Protocol
it	O
merely	O
increments	O
the	O
hop	O
count	O
in	O
the	O
overloaded	O
fragment	O
id	O
field	O
.	O
</s>
<s>
Song	O
and	O
Perrig	O
identify	O
that	O
this	O
is	O
not	O
robust	O
enough	O
against	O
collisions	O
and	O
thus	O
suggest	O
using	O
a	O
set	O
of	O
independent	O
hash	B-Error_Name
functions	I-Error_Name
,	O
randomly	O
selecting	O
one	O
,	O
and	O
then	O
hashing	O
the	O
IP	B-Protocol
along	O
with	O
a	O
FID	O
or	O
function	O
id	O
and	O
then	O
encoding	O
this	O
.	O
</s>
<s>
Belenky	O
and	O
Ansari	O
,	O
outline	O
a	O
deterministic	O
packet	B-Protocol
marking	O
scheme	O
.	O
</s>
<s>
They	O
describe	O
a	O
more	O
realistic	O
topology	O
for	O
the	O
Internet	O
–	O
that	O
is	O
composed	O
of	O
LANs	O
and	O
ASs	O
with	O
a	O
connective	O
boundary	O
–	O
and	O
attempt	O
to	O
put	O
a	O
single	O
mark	O
on	O
inbound	O
packets	B-Protocol
at	O
the	O
point	O
of	O
network	O
ingress	O
.	O
</s>
<s>
Their	O
idea	O
is	O
to	O
put	O
,	O
with	O
random	O
probability	O
of	O
.5	O
,	O
the	O
upper	O
or	O
lower	O
half	O
of	O
the	O
IP	B-Protocol
address	I-Protocol
of	O
the	O
ingress	O
interface	O
into	O
the	O
fragment	O
id	O
field	O
of	O
the	O
packet	B-Protocol
,	O
and	O
then	O
set	O
a	O
reserve	O
bit	O
indicating	O
which	O
portion	O
of	O
the	O
address	O
is	O
contained	O
in	O
the	O
fragment	O
field	O
.	O
</s>
<s>
By	O
using	O
this	O
approach	O
they	O
claim	O
to	O
be	O
able	O
to	O
obtain	O
0	O
false	O
positives	O
with	O
.99	O
probability	O
after	O
only	O
7	O
packets	B-Protocol
.	O
</s>
<s>
Their	O
approach	O
is	O
similar	O
in	O
that	O
they	O
wish	O
to	O
use	O
and	O
encoded	O
IP	B-Protocol
address	I-Protocol
of	O
the	O
input	O
interface	O
in	O
the	O
fragment	O
id	O
field	O
of	O
the	O
packet	B-Protocol
.	O
</s>
<s>
Where	O
they	O
differ	O
from	O
Belenky	O
and	O
Ansari	O
is	O
that	O
they	O
wish	O
to	O
encode	O
the	O
IP	B-Protocol
address	I-Protocol
as	O
a	O
16-bit	O
hash	B-Error_Name
of	O
that	O
IP	B-Protocol
address	I-Protocol
.	O
</s>
<s>
Initially	O
they	O
choose	O
a	O
known	O
hashing	B-Error_Name
function	I-Error_Name
.	O
</s>
<s>
They	O
attempt	O
to	O
mitigate	O
the	O
collision	O
problem	O
by	O
introducing	O
a	O
random	O
distributed	O
selection	O
of	O
a	O
hash	B-Error_Name
function	I-Error_Name
from	O
the	O
universal	O
set	O
,	O
and	O
then	O
applying	O
it	O
to	O
the	O
IP	B-Protocol
address	I-Protocol
.	O
</s>
<s>
In	O
either	O
hashing	O
scenario	O
,	O
the	O
source	O
address	O
and	O
the	O
hash	B-Error_Name
are	O
mapped	O
together	O
in	O
a	O
table	O
for	O
later	O
look-up	O
along	O
with	O
a	O
bit	O
indicating	O
which	O
portion	O
of	O
the	O
address	O
they	O
have	O
received	O
.	O
</s>
<s>
Through	O
a	O
complicated	O
procedure	O
and	O
a	O
random	O
hash	B-Error_Name
selection	O
,	O
they	O
are	O
capable	O
of	O
reducing	O
address	O
collision	O
.	O
</s>
<s>
By	O
using	O
a	O
deterministic	O
approach	O
they	O
reduce	O
the	O
time	O
for	O
their	O
reconstruction	O
procedure	O
for	O
their	O
mark	O
(	O
the	O
16-bit	O
hash	B-Error_Name
)	O
.	O
</s>
<s>
Shokri	O
and	O
Varshovi	O
introduced	O
the	O
concepts	O
of	O
Dynamic	O
Marking	O
and	O
Mark-based	O
Detection	O
with	O
"	O
Dynamic	O
Deterministic	O
Packet	B-Protocol
Marking	O
,	O
"	O
(	O
DDPM	O
)	O
.	O
</s>
<s>
In	O
the	O
case	O
of	O
a	O
DRDoS	O
it	O
enables	O
the	O
victim	O
to	O
trace	O
the	O
attack	O
one	O
step	O
further	O
back	O
to	O
the	O
source	O
,	O
to	O
find	O
a	O
master	O
machine	O
or	O
the	O
real	O
attacker	O
with	O
only	O
a	O
few	O
numbers	O
of	O
packets	B-Protocol
.	O
</s>
<s>
In	O
the	O
mark-based	O
method	O
,	O
the	O
detection	O
engine	O
takes	O
into	O
account	O
the	O
marks	O
of	O
the	O
packets	B-Protocol
to	O
identify	O
varying	O
sources	O
of	O
a	O
single	O
site	O
involved	O
in	O
a	O
DDoS	O
attack	O
.	O
</s>
<s>
In	O
order	O
to	O
satisfy	O
the	O
end-to-end	O
arguments	O
approach	O
,	O
fate-sharing	B-Application
and	O
also	O
respect	O
to	O
the	O
need	O
for	O
scalable	O
and	O
applicable	O
schemes	O
,	O
only	O
edge	O
routers	O
implement	O
a	O
simple	O
marking	O
procedure	O
.	O
</s>
<s>
S	O
.	O
Majumdar	O
,	O
D	O
.	O
Kulkarni	O
and	O
C	O
.	O
Ravishankar	O
proposes	O
a	O
new	O
method	O
to	O
traceback	O
the	O
origin	O
of	O
DHCP	B-Protocol
packets	B-Protocol
in	O
ICDCN	O
2011	O
.	O
</s>
<s>
Their	O
method	O
adds	O
a	O
new	O
DHCP	B-Protocol
option	O
that	O
contains	O
the	O
MAC	O
address	O
and	O
the	O
ingress	O
port	O
of	O
the	O
edge	O
switch	O
which	O
had	O
received	O
the	O
DHCP	B-Protocol
packet	B-Protocol
.	O
</s>
<s>
This	O
new	O
option	O
will	O
be	O
added	O
to	O
the	O
DHCP	B-Protocol
packet	B-Protocol
by	O
the	O
edge	O
switch	O
.	O
</s>
<s>
This	O
solution	O
follows	O
DHCP	B-Protocol
RFCs	O
.	O
</s>
<s>
Previous	O
IP	B-Protocol
traceback	I-Protocol
mechanisms	O
have	O
overloaded	O
IP	B-Protocol
header	O
fields	O
with	O
traceback	O
information	O
and	O
thus	O
are	O
violating	O
IP	B-Protocol
RFCs	O
.	O
</s>
<s>
However	O
,	O
this	O
approach	O
is	O
not	O
applicable	O
to	O
any	O
general	O
IP	B-Protocol
packet	B-Protocol
.	O
</s>
<s>
With	O
router-based	O
approaches	O
,	O
the	O
router	O
is	O
charged	O
with	O
maintaining	O
information	O
regarding	O
packets	B-Protocol
that	O
pass	O
through	O
it	O
.	O
</s>
<s>
For	O
example	O
,	O
Sager	O
proposes	O
to	O
log	O
packets	B-Protocol
and	O
then	O
data	O
mine	O
them	O
later	O
.	O
</s>
<s>
The	O
idea	O
proposed	O
in	O
their	O
paper	O
is	O
to	O
generate	O
a	O
fingerprint	O
of	O
the	O
packet	B-Protocol
,	O
based	O
upon	O
the	O
invariant	O
portions	O
of	O
the	O
packet	B-Protocol
(	O
source	O
,	O
destination	O
,	O
etc	O
.	O
)	O
</s>
<s>
More	O
specifically	O
,	O
m	O
independent	O
simple	O
hash	B-Error_Name
functions	I-Error_Name
each	O
generate	O
an	O
output	O
in	O
the	O
range	O
of	O
2n-1	O
.	O
</s>
<s>
A	O
bit	O
is	O
then	O
set	O
at	O
the	O
index	O
generated	O
to	O
create	O
a	O
fingerprint	O
when	O
combined	O
with	O
the	O
output	O
of	O
all	O
other	O
hash	B-Error_Name
functions	I-Error_Name
.	O
</s>
<s>
The	O
paper	O
shows	O
a	O
simple	O
family	O
of	O
hash	B-Error_Name
functions	I-Error_Name
suitable	O
for	O
this	O
purpose	O
and	O
present	O
a	O
hardware	O
implementation	O
of	O
it	O
.	O
</s>
<s>
A	O
small	O
n	O
makes	O
the	O
probability	O
of	O
collision	O
of	O
packet	B-Protocol
hashes	B-Error_Name
(	O
and	O
false	O
identification	O
)	O
higher	O
.	O
</s>
<s>
When	O
a	O
packet	B-Protocol
is	O
to	O
be	O
traced	O
back	O
,	O
it	O
is	O
forwarded	O
to	O
originating	O
routers	O
where	O
fingerprint	O
matches	O
are	O
checked	O
.	O
</s>
<s>
As	O
time	O
passes	O
,	O
the	O
fingerprint	O
information	O
is	O
“	O
clobbered	O
”	O
by	O
hashes	B-Error_Name
generated	O
by	O
other	O
packets	B-Protocol
.	O
</s>
<s>
Thus	O
,	O
the	O
selectivity	O
of	O
this	O
approach	O
degrades	O
with	O
the	O
time	O
that	O
has	O
passed	O
between	O
the	O
passage	O
of	O
the	O
packet	B-Protocol
and	O
the	O
traceback	O
interrogation	O
.	O
</s>
<s>
In	O
their	O
approach	O
,	O
they	O
wish	O
to	O
integrate	O
the	O
SPIE	O
approach	O
as	O
outlined	O
by	O
Snoeren	O
,	O
with	O
their	O
approach	O
of	O
recording	O
the	O
layer	O
2	O
link-id	O
along	O
with	O
the	O
network	O
ID	O
(	O
VLAN	B-General_Concept
or	O
true	O
ID	O
)	O
,	O
the	O
MAC	O
address	O
of	O
the	O
layer	O
2	O
switch	O
that	O
received	O
the	O
packet	B-Protocol
and	O
the	O
link	O
id	O
it	O
came	O
in	O
on	O
.	O
</s>
<s>
They	O
rely	O
on	O
the	O
MAC:port	O
tuple	O
as	O
a	O
method	O
of	O
tracing	O
a	O
packet	B-Protocol
back	O
(	O
even	O
if	O
the	O
MAC	O
address	O
has	O
been	O
spoofed	O
)	O
.	O
</s>
<s>
They	O
admit	O
their	O
algorithm	O
is	O
slow	O
(O(N2 )	O
)	O
and	O
with	O
only	O
3.3	O
million	O
packet	B-Protocol
hashes	B-Error_Name
being	O
stored	O
the	O
approximate	O
time	O
before	O
the	O
digest	O
tables	O
are	O
invalid	O
is	O
1	O
minute	O
.	O
</s>
<s>
The	O
ICMP	O
traceback	O
scheme	O
Steven	O
M	O
.	O
Bellovin	O
proposes	O
probabilistically	O
sending	O
an	O
ICMP	O
traceback	O
packet	B-Protocol
forward	O
to	O
the	O
destination	O
host	O
of	O
an	O
IP	B-Protocol
packet	B-Protocol
with	O
some	O
low	O
probability	O
.	O
</s>
<s>
Thus	O
,	O
the	O
need	O
to	O
maintain	O
state	O
in	O
either	O
the	O
packet	B-Protocol
or	O
the	O
router	O
is	O
obviated	O
.	O
</s>
<s>
To	O
bypass	O
this	O
restriction	O
and	O
automate	O
this	O
process	O
,	O
Stone	O
proposes	O
routing	O
suspicious	O
packets	B-Protocol
on	O
an	O
overlay	B-Architecture
network	I-Architecture
using	O
ISP	O
edge	O
routers	O
.	O
</s>
<s>
By	O
simplifying	O
the	O
topology	O
,	O
suspicious	O
packets	B-Protocol
can	O
easily	O
be	O
re-routed	O
to	O
a	O
specialized	O
network	O
for	O
further	O
analysis	O
.	O
</s>
<s>
Flooding	O
a	O
link	O
will	O
cause	O
all	O
packets	B-Protocol
,	O
including	O
packets	B-Protocol
from	O
the	O
attacker	O
,	O
to	O
be	O
dropped	O
with	O
the	O
same	O
probability	O
.	O
</s>
<s>
We	O
can	O
conclude	O
from	O
this	O
that	O
if	O
a	O
given	O
link	O
were	O
flooded	O
,	O
and	O
packets	B-Protocol
from	O
the	O
attacker	O
slowed	O
,	O
then	O
this	O
link	O
must	O
be	O
part	O
of	O
the	O
attack	O
path	O
.	O
</s>
<s>
The	O
traceback	O
problem	O
is	O
complicated	O
because	O
of	O
spoofed	O
packets	B-Protocol
.	O
</s>
<s>
Thus	O
,	O
a	O
related	O
effort	O
is	O
targeted	O
towards	O
preventing	O
spoofed	O
packets	B-Protocol
;	O
known	O
as	O
ingress	O
filtering	O
.	O
</s>
<s>
Ingress	O
Filtering	O
restricts	O
spoofed	O
packets	B-Protocol
at	O
ingress	O
points	O
to	O
the	O
network	O
by	O
tracking	O
the	O
set	O
of	O
legitimate	O
source	O
networks	O
that	O
can	O
use	O
this	O
router	O
.	O
</s>
<s>
They	O
present	O
a	O
means	O
of	O
detecting	O
false	O
packets	B-Protocol
,	O
at	O
least	O
to	O
the	O
subnet	O
,	O
by	O
essentially	O
making	O
use	O
of	O
existing	O
OSPF	B-Protocol
routing	O
state	O
to	O
have	O
routers	O
make	O
intelligent	O
decisions	O
about	O
whether	O
or	O
not	O
a	O
packet	B-Protocol
should	O
be	O
routed	O
.	O
</s>
