<s>
In	O
computer	B-Architecture
networking	I-Architecture
,	O
a	O
proxy	B-Application
server	I-Application
is	O
a	O
server	B-Application
application	I-Application
that	O
acts	O
as	O
an	O
intermediary	O
between	O
a	O
client	B-Protocol
requesting	O
a	O
resource	O
and	O
the	O
server	B-Application
providing	O
that	O
resource	O
.	O
</s>
<s>
Instead	O
of	O
connecting	O
directly	O
to	O
a	O
server	B-Application
that	O
can	O
fulfill	O
a	O
request	O
for	O
a	O
resource	O
,	O
such	O
as	O
a	O
file	O
or	O
web	O
page	O
,	O
the	O
client	B-Protocol
directs	O
the	O
request	O
to	O
the	O
proxy	B-Application
server	I-Application
,	O
which	O
evaluates	O
the	O
request	O
and	O
performs	O
the	O
required	O
network	O
transactions	O
.	O
</s>
<s>
This	O
serves	O
as	O
a	O
method	O
to	O
simplify	O
or	O
control	O
the	O
complexity	O
of	O
the	O
request	O
,	O
or	O
provide	O
additional	O
benefits	O
such	O
as	O
load	B-Application
balancing	I-Application
,	O
privacy	O
,	O
or	O
security	O
.	O
</s>
<s>
Proxies	O
were	O
devised	O
to	O
add	O
structure	O
and	O
encapsulation	B-Protocol
to	O
distributed	B-Architecture
systems	I-Architecture
.	O
</s>
<s>
A	O
proxy	B-Application
server	I-Application
thus	O
functions	O
on	O
behalf	O
of	O
the	O
client	B-Protocol
when	O
requesting	O
service	O
,	O
potentially	O
masking	O
the	O
true	O
origin	O
of	O
the	O
request	O
to	O
the	O
resource	O
server	B-Application
.	O
</s>
<s>
A	O
proxy	B-Application
server	I-Application
may	O
reside	O
on	O
the	O
user	O
's	O
local	O
computer	O
,	O
or	O
at	O
any	O
point	O
between	O
the	O
user	O
's	O
computer	O
and	O
destination	O
servers	O
on	O
the	O
Internet	O
.	O
</s>
<s>
A	O
proxy	B-Application
server	I-Application
that	O
passes	O
unmodified	O
requests	O
and	O
responses	O
is	O
usually	O
called	O
a	O
gateway	B-Application
or	O
sometimes	O
a	O
tunneling	O
proxy	O
.	O
</s>
<s>
A	O
reverse	B-General_Concept
proxy	I-General_Concept
is	O
usually	O
an	O
internal-facing	O
proxy	O
used	O
as	O
a	O
front-end	O
to	O
control	O
and	O
protect	O
access	O
to	O
a	O
server	B-Application
on	O
a	O
private	O
network	O
.	O
</s>
<s>
A	O
reverse	B-General_Concept
proxy	I-General_Concept
commonly	O
also	O
performs	O
tasks	O
such	O
as	O
load-balancing	B-Application
,	O
authentication	B-Protocol
,	O
decryption	O
and	O
caching	B-General_Concept
.	O
</s>
<s>
An	O
open	B-Protocol
proxy	I-Protocol
is	O
a	O
forwarding	B-Protocol
proxy	B-Application
server	I-Application
that	O
is	O
accessible	O
by	O
any	O
Internet	O
user	O
.	O
</s>
<s>
In	O
2008	O
,	O
network	O
security	O
expert	O
Gordon	O
Lyon	O
estimated	O
that	O
"	O
hundreds	O
of	O
thousands	O
"	O
of	O
open	B-Protocol
proxies	I-Protocol
are	O
operated	O
on	O
the	O
Internet	O
.	O
</s>
<s>
Anonymous	O
proxy	O
–	O
This	O
server	B-Application
reveals	O
its	O
identity	O
as	O
a	O
proxy	B-Application
server	I-Application
but	O
does	O
not	O
disclose	O
the	O
originating	O
IP	B-Protocol
address	I-Protocol
of	O
the	O
client	B-Protocol
.	O
</s>
<s>
Although	O
this	O
type	O
of	O
server	B-Application
can	O
be	O
discovered	O
easily	O
,	O
it	O
can	O
be	O
beneficial	O
for	O
some	O
users	O
as	O
it	O
hides	O
the	O
originating	O
IP	B-Protocol
address	I-Protocol
.	O
</s>
<s>
Transparent	O
proxy	O
–	O
This	O
server	B-Application
not	O
only	O
identifies	O
itself	O
as	O
a	O
proxy	B-Application
server	I-Application
but	O
with	O
the	O
support	O
of	O
HTTP	B-Protocol
header	I-Protocol
fields	I-Protocol
such	O
as	O
X-Forwarded-For	O
,	O
the	O
originating	O
IP	B-Protocol
address	I-Protocol
can	O
be	O
retrieved	O
as	O
well	O
.	O
</s>
<s>
The	O
main	O
benefit	O
of	O
using	O
this	O
type	O
of	O
server	B-Application
is	O
its	O
ability	O
to	O
cache	B-Protocol
a	O
website	O
for	O
faster	O
retrieval	O
.	O
</s>
<s>
A	O
reverse	B-General_Concept
proxy	I-General_Concept
(	O
or	O
surrogate	O
)	O
is	O
a	O
proxy	B-Application
server	I-Application
that	O
appears	O
to	O
clients	O
to	O
be	O
an	O
ordinary	O
server	B-Application
.	O
</s>
<s>
Reverse	B-General_Concept
proxies	I-General_Concept
forward	O
requests	O
to	O
one	O
or	O
more	O
ordinary	O
servers	O
that	O
handle	O
the	O
request	O
.	O
</s>
<s>
The	O
response	O
from	O
the	O
proxy	B-Application
server	I-Application
is	O
returned	O
as	O
if	O
it	O
came	O
directly	O
from	O
the	O
original	O
server	B-Application
,	O
leaving	O
the	O
client	B-Protocol
with	O
no	O
knowledge	O
of	O
the	O
original	O
server	B-Application
.	O
</s>
<s>
Reverse	B-General_Concept
proxies	I-General_Concept
are	O
installed	O
in	O
the	O
neighborhood	O
of	O
one	O
or	O
more	O
web	O
servers	O
.	O
</s>
<s>
All	O
traffic	O
coming	O
from	O
the	O
Internet	O
and	O
with	O
a	O
destination	O
of	O
one	O
of	O
the	O
neighborhood	O
's	O
web	O
servers	O
goes	O
through	O
the	O
proxy	B-Application
server	I-Application
.	O
</s>
<s>
The	O
use	O
of	O
reverse	O
originates	O
in	O
its	O
counterpart	O
forward	O
proxy	O
since	O
the	O
reverse	B-General_Concept
proxy	I-General_Concept
sits	O
closer	O
to	O
the	O
web	O
server	B-Application
and	O
serves	O
only	O
a	O
restricted	O
set	O
of	O
websites	O
.	O
</s>
<s>
There	O
are	O
several	O
reasons	O
for	O
installing	O
reverse	B-General_Concept
proxy	I-General_Concept
servers	O
:	O
</s>
<s>
Encryption/SSL	O
acceleration	O
:	O
when	O
secure	O
websites	O
are	O
created	O
,	O
the	O
Secure	B-Protocol
Sockets	I-Protocol
Layer	I-Protocol
(	O
SSL	O
)	O
encryption	O
is	O
often	O
not	O
done	O
by	O
the	O
web	O
server	B-Application
itself	O
,	O
but	O
by	O
a	O
reverse	B-General_Concept
proxy	I-General_Concept
that	O
is	O
equipped	O
with	O
SSL	O
acceleration	O
hardware	O
.	O
</s>
<s>
Furthermore	O
,	O
a	O
host	O
can	O
provide	O
a	O
single	O
"	O
SSL	B-Application
proxy	I-Application
"	O
to	O
provide	O
SSL	B-Protocol
encryption	I-Protocol
for	O
an	O
arbitrary	O
number	O
of	O
hosts	O
,	O
removing	O
the	O
need	O
for	O
a	O
separate	O
SSL	O
server	B-Application
certificate	O
for	O
each	O
host	O
,	O
with	O
the	O
downside	O
that	O
all	O
hosts	O
behind	O
the	O
SSL	B-Application
proxy	I-Application
have	O
to	O
share	O
a	O
common	O
DNS	B-Protocol
name	I-Protocol
or	O
IP	B-Protocol
address	I-Protocol
for	O
SSL	O
connections	O
.	O
</s>
<s>
This	O
problem	O
can	O
partly	O
be	O
overcome	O
by	O
using	O
the	O
SubjectAltName	O
feature	O
of	O
X.509	O
certificates	O
or	O
the	O
SNI	B-Protocol
extension	I-Protocol
of	O
TLS	B-Protocol
.	O
</s>
<s>
Load	B-Application
balancing	I-Application
:	O
the	O
reverse	B-General_Concept
proxy	I-General_Concept
can	O
distribute	O
the	O
load	O
to	O
several	O
web	O
servers	O
,	O
each	O
web	O
server	B-Application
serving	O
its	O
own	O
application	O
area	O
.	O
</s>
<s>
In	O
such	O
a	O
case	O
,	O
the	O
reverse	B-General_Concept
proxy	I-General_Concept
may	O
need	O
to	O
rewrite	O
the	O
URLs	O
in	O
each	O
web	O
page	O
(	O
translation	O
from	O
externally	O
known	O
URLs	O
to	O
the	O
internal	O
locations	O
)	O
.	O
</s>
<s>
Serve/cache	O
static	O
content	O
:	O
A	O
reverse	B-General_Concept
proxy	I-General_Concept
can	O
offload	O
the	O
web	O
servers	O
by	O
caching	B-General_Concept
static	O
content	O
like	O
pictures	O
and	O
other	O
static	O
graphical	O
content	O
.	O
</s>
<s>
Compression	B-General_Concept
:	O
the	O
proxy	B-Application
server	I-Application
can	O
optimize	O
and	O
compress	O
the	O
content	O
to	O
speed	O
up	O
the	O
load	O
time	O
.	O
</s>
<s>
Spoon	O
feeding	O
:	O
reduces	O
resource	O
usage	O
caused	O
by	O
slow	O
clients	O
on	O
the	O
web	O
servers	O
by	O
caching	B-General_Concept
the	O
content	O
the	O
web	O
server	B-Application
sent	O
and	O
slowly	O
"	O
spoon	O
feeding	O
"	O
it	O
to	O
the	O
client	B-Protocol
.	O
</s>
<s>
Security	O
:	O
the	O
proxy	B-Application
server	I-Application
is	O
an	O
additional	O
layer	O
of	O
defense	O
and	O
can	O
protect	O
against	O
some	O
OS	O
and	O
web-server-specific	O
attacks	O
.	O
</s>
<s>
Extranet	B-Architecture
publishing	O
:	O
a	O
reverse	B-General_Concept
proxy	I-General_Concept
server	B-Application
facing	O
the	O
Internet	O
can	O
be	O
used	O
to	O
communicate	O
to	O
a	O
firewall	B-Application
server	B-Application
internal	O
to	O
an	O
organization	O
,	O
providing	O
extranet	B-Architecture
access	O
to	O
some	O
functions	O
while	O
keeping	O
the	O
servers	O
behind	O
the	O
firewalls	B-Application
.	O
</s>
<s>
If	O
used	O
in	O
this	O
way	O
,	O
security	O
measures	O
should	O
be	O
considered	O
to	O
protect	O
the	O
rest	O
of	O
your	O
infrastructure	O
in	O
case	O
this	O
server	B-Application
is	O
compromised	O
,	O
as	O
its	O
web	O
application	O
is	O
exposed	O
to	O
attack	O
from	O
the	O
Internet	O
.	O
</s>
<s>
A	O
content-filtering	B-Protocol
web	O
proxy	B-Application
server	I-Application
provides	O
administrative	O
control	O
over	O
the	O
content	O
that	O
may	O
be	O
relayed	O
in	O
one	O
or	O
both	O
directions	O
through	O
the	O
proxy	O
.	O
</s>
<s>
It	O
is	O
commonly	O
used	O
in	O
both	O
commercial	O
and	O
non-commercial	O
organizations	O
(	O
especially	O
schools	O
)	O
to	O
ensure	O
that	O
Internet	O
usage	O
conforms	O
to	O
acceptable	B-Application
use	I-Application
policy	I-Application
.	O
</s>
<s>
Content	B-Protocol
filtering	I-Protocol
proxy	B-Application
servers	I-Application
will	O
often	O
support	O
user	O
authentication	B-Protocol
to	O
control	O
web	O
access	O
.	O
</s>
<s>
It	O
also	O
usually	O
produces	O
logs	B-Application
,	O
either	O
to	O
give	O
detailed	O
information	O
about	O
the	O
URLs	O
accessed	O
by	O
specific	O
users	O
or	O
to	O
monitor	O
bandwidth	O
usage	O
statistics	O
.	O
</s>
<s>
It	O
may	O
also	O
communicate	O
to	O
daemon-based	O
and/or	O
ICAP-based	O
antivirus	O
software	O
to	O
provide	O
security	O
against	O
viruses	O
and	O
other	O
malware	O
by	O
scanning	O
incoming	O
content	O
in	O
real-time	O
before	O
it	O
enters	O
the	O
network	O
.	O
</s>
<s>
This	O
is	O
done	O
either	O
with	O
a	O
specialized	O
proxy	O
,	O
called	O
a	O
content	B-Protocol
filter	I-Protocol
(	O
both	O
commercial	O
and	O
free	O
products	O
are	O
available	O
)	O
,	O
or	O
by	O
using	O
a	O
cache-extension	O
protocol	O
such	O
as	O
ICAP	B-Protocol
,	O
that	O
allows	O
plug-in	O
extensions	O
to	O
an	O
open	O
caching	B-General_Concept
architecture	O
.	O
</s>
<s>
Requests	O
may	O
be	O
filtered	O
by	O
several	O
methods	O
,	O
such	O
as	O
a	O
URL	O
or	O
DNS	B-Protocol
blacklists	O
,	O
URL	O
regex	O
filtering	O
,	O
MIME	B-Protocol
filtering	O
,	O
or	O
content	O
keyword	O
filtering	O
.	O
</s>
<s>
If	O
the	O
content	O
is	O
rejected	O
then	O
an	O
HTTP	B-Protocol
fetch	O
error	O
may	O
be	O
returned	O
to	O
the	O
requester	O
.	O
</s>
<s>
Most	O
web	B-Protocol
filtering	I-Protocol
companies	O
use	O
an	O
internet-wide	O
crawling	O
robot	O
that	O
assesses	O
the	O
likelihood	O
that	O
content	O
is	O
a	O
certain	O
type	O
.	O
</s>
<s>
Web	B-Protocol
filtering	I-Protocol
proxies	O
are	O
not	O
able	O
to	O
peer	O
inside	O
secure	B-Protocol
sockets	I-Protocol
HTTP	B-Protocol
transactions	O
,	O
assuming	O
the	O
chain-of-trust	O
of	O
SSL/TLS	B-Protocol
(	O
Transport	B-Protocol
Layer	I-Protocol
Security	I-Protocol
)	O
has	O
not	O
been	O
tampered	O
with	O
.	O
</s>
<s>
The	O
SSL/TLS	B-Protocol
chain-of-trust	O
relies	O
on	O
trusted	O
root	O
certificate	B-Architecture
authorities	I-Architecture
.	O
</s>
<s>
In	O
a	O
workplace	O
setting	O
where	O
the	O
client	B-Protocol
is	O
managed	O
by	O
the	O
organization	O
,	O
devices	O
may	O
be	O
configured	O
to	O
trust	O
a	O
root	O
certificate	O
whose	O
private	O
key	O
is	O
known	O
to	O
the	O
proxy	O
.	O
</s>
<s>
In	O
such	O
situations	O
,	O
proxy	O
analysis	O
of	O
the	O
contents	O
of	O
an	O
SSL/TLS	B-Protocol
transaction	O
becomes	O
possible	O
.	O
</s>
<s>
The	O
proxy	O
is	O
effectively	O
operating	O
a	O
man-in-the-middle	O
attack	O
,	O
allowed	O
by	O
the	O
client	B-Protocol
's	O
trust	O
of	O
a	O
root	O
certificate	O
the	O
proxy	O
owns	O
.	O
</s>
<s>
If	O
the	O
destination	O
server	B-Application
filters	O
content	O
based	O
on	O
the	O
origin	O
of	O
the	O
request	O
,	O
the	O
use	O
of	O
a	O
proxy	O
can	O
circumvent	O
this	O
filter	O
.	O
</s>
<s>
For	O
example	O
,	O
a	O
server	B-Application
using	O
IP-based	O
geolocation	O
to	O
restrict	O
its	O
service	O
to	O
a	O
certain	O
country	O
can	O
be	O
accessed	O
using	O
a	O
proxy	O
located	O
in	O
that	O
country	O
to	O
access	O
the	O
service	O
.	O
</s>
<s>
Proxies	O
can	O
be	O
installed	O
in	O
order	O
to	O
eavesdrop	O
upon	O
the	O
data-flow	O
between	O
client	B-Protocol
machines	I-Protocol
and	O
the	O
web	O
.	O
</s>
<s>
All	O
content	O
sent	O
or	O
accessed	O
–	O
including	O
passwords	O
submitted	O
and	O
cookies	B-Application
used	O
–	O
can	O
be	O
captured	O
and	O
analyzed	O
by	O
the	O
proxy	O
operator	O
.	O
</s>
<s>
In	O
what	O
is	O
more	O
of	O
an	O
inconvenience	O
than	O
a	O
risk	O
,	O
proxy	O
users	O
may	O
find	O
themselves	O
being	O
blocked	O
from	O
certain	O
Web	O
sites	O
,	O
as	O
numerous	O
forums	O
and	O
Web	O
sites	O
block	O
IP	B-Protocol
addresses	I-Protocol
from	O
proxies	O
known	O
to	O
have	O
spammed	O
or	O
trolled	O
the	O
site	O
.	O
</s>
<s>
Proxy	B-Application
bouncing	I-Application
can	O
be	O
used	O
to	O
maintain	O
privacy	O
.	O
</s>
<s>
A	O
caching	B-General_Concept
proxy	B-Application
server	I-Application
accelerates	O
service	O
requests	O
by	O
retrieving	O
the	O
content	O
saved	O
from	O
a	O
previous	O
request	O
made	O
by	O
the	O
same	O
client	B-Protocol
or	O
even	O
other	O
clients	O
.	O
</s>
<s>
Caching	B-General_Concept
proxies	O
keep	O
local	O
copies	O
of	O
frequently	O
requested	O
resources	O
,	O
allowing	O
large	O
organizations	O
to	O
significantly	O
reduce	O
their	O
upstream	O
bandwidth	O
usage	O
and	O
costs	O
,	O
while	O
significantly	O
increasing	O
performance	O
.	O
</s>
<s>
Most	O
ISPs	O
and	O
large	O
businesses	O
have	O
a	O
caching	B-General_Concept
proxy	O
.	O
</s>
<s>
Caching	B-General_Concept
proxies	O
were	O
the	O
first	O
kind	O
of	O
proxy	B-Application
server	I-Application
.	O
</s>
<s>
Web	O
proxies	O
are	O
commonly	O
used	O
to	O
cache	B-Protocol
web	O
pages	O
from	O
a	O
web	O
server	B-Application
.	O
</s>
<s>
Poorly	O
implemented	O
caching	B-General_Concept
proxies	O
can	O
cause	O
problems	O
,	O
such	O
as	O
an	O
inability	O
to	O
use	O
user	O
authentication	B-Protocol
.	O
</s>
<s>
These	O
are	O
typically	O
used	O
to	O
improve	O
TCP	B-Protocol
performance	O
in	O
the	O
presence	O
of	O
high	O
round-trip	O
times	O
or	O
high	O
packet	B-Protocol
loss	O
(	O
such	O
as	O
wireless	O
or	O
mobile	O
phone	O
networks	O
)	O
;	O
or	O
highly	O
asymmetric	O
links	O
featuring	O
very	O
different	O
upload	O
and	O
download	O
rates	O
.	O
</s>
<s>
PEPs	O
can	O
make	O
more	O
efficient	O
use	O
of	O
the	O
network	O
,	O
for	O
example	O
,	O
by	O
merging	O
TCP	B-Protocol
ACKs	B-Protocol
(	O
acknowledgements	B-Protocol
)	O
or	O
compressing	O
data	O
sent	O
at	O
the	O
application	B-Application
layer	I-Application
.	O
</s>
<s>
A	O
translation	O
proxy	O
is	O
a	O
proxy	B-Application
server	I-Application
that	O
is	O
used	O
to	O
localize	O
a	O
website	O
experience	O
for	O
different	O
markets	O
.	O
</s>
<s>
An	O
anonymous	B-Application
proxy	I-Application
server	I-Application
(	O
sometimes	O
called	O
a	O
web	O
proxy	O
)	O
generally	O
attempts	O
to	O
anonymize	O
web	O
surfing	O
.	O
</s>
<s>
The	O
destination	O
server	B-Application
(	O
the	O
server	B-Application
that	O
ultimately	O
satisfies	O
the	O
web	O
request	O
)	O
receives	O
requests	O
from	O
the	O
anonymizing	O
proxy	B-Application
server	I-Application
and	O
thus	O
does	O
not	O
receive	O
information	O
about	O
the	O
end	O
user	O
's	O
address	O
.	O
</s>
<s>
The	O
requests	O
are	O
not	O
anonymous	O
to	O
the	O
anonymizing	O
proxy	B-Application
server	I-Application
,	O
however	O
,	O
and	O
so	O
a	O
degree	O
of	O
trust	O
is	O
present	O
between	O
the	O
proxy	B-Application
server	I-Application
and	O
the	O
user	O
.	O
</s>
<s>
Many	O
proxy	B-Application
servers	I-Application
are	O
funded	O
through	O
a	O
continued	O
advertising	O
link	O
to	O
the	O
user	O
.	O
</s>
<s>
Access	O
control	O
:	O
Some	O
proxy	B-Application
servers	I-Application
implement	O
a	O
logon	O
requirement	O
.	O
</s>
<s>
Some	O
anonymizing	O
proxy	B-Application
servers	I-Application
may	O
forward	O
data	B-Protocol
packets	I-Protocol
with	O
header	O
lines	O
such	O
as	O
HTTP_VIA	O
,	O
HTTP_X_FORWARDED_FOR	O
,	O
or	O
HTTP_FORWARDED	O
,	O
which	O
may	O
reveal	O
the	O
IP	B-Protocol
address	I-Protocol
of	O
the	O
client	B-Protocol
.	O
</s>
<s>
Other	O
anonymizing	O
proxy	B-Application
servers	I-Application
,	O
known	O
as	O
elite	O
or	O
high-anonymity	O
proxies	O
,	O
make	O
it	O
appear	O
that	O
the	O
proxy	B-Application
server	I-Application
is	O
the	O
client	B-Protocol
.	O
</s>
<s>
A	O
website	O
could	O
still	O
suspect	O
a	O
proxy	O
is	O
being	O
used	O
if	O
the	O
client	B-Protocol
sends	O
packets	B-Protocol
that	O
include	O
a	O
cookie	B-Application
from	O
a	O
previous	O
visit	O
that	O
did	O
not	O
use	O
the	O
high-anonymity	O
proxy	B-Application
server	I-Application
.	O
</s>
<s>
Clearing	O
cookies	B-Application
,	O
and	O
possibly	O
the	O
cache	B-Protocol
,	O
would	O
solve	O
this	O
problem	O
.	O
</s>
<s>
Advertisers	O
use	O
proxy	B-Application
servers	I-Application
for	O
validating	O
,	O
checking	O
and	O
quality	O
assurance	O
of	O
geotargeted	O
ads	O
.	O
</s>
<s>
A	O
geotargeting	O
ad	O
server	B-Application
checks	O
the	O
request	O
source	O
IP	B-Protocol
address	I-Protocol
and	O
uses	O
a	O
geo-IP	B-Application
database	I-Application
to	O
determine	O
the	O
geographic	O
source	O
of	O
requests	O
.	O
</s>
<s>
Using	O
a	O
proxy	B-Application
server	I-Application
that	O
is	O
physically	O
located	O
inside	O
a	O
specific	O
country	O
or	O
a	O
city	O
gives	O
advertisers	O
the	O
ability	O
to	O
test	O
geotargeted	O
ads	O
.	O
</s>
<s>
A	O
proxy	O
can	O
keep	O
the	O
internal	O
network	O
structure	O
of	O
a	O
company	O
secret	O
by	O
using	O
network	B-Protocol
address	I-Protocol
translation	I-Protocol
,	O
which	O
can	O
help	O
the	O
security	O
of	O
the	O
internal	O
network	O
.	O
</s>
<s>
Proxies	O
can	O
also	O
be	O
combined	O
with	O
firewalls	B-Application
.	O
</s>
<s>
when	O
cross-domain	B-Protocol
restrictions	I-Protocol
prohibit	O
the	O
web	O
site	O
from	O
linking	O
directly	O
to	O
the	O
outside	O
domains	O
.	O
</s>
<s>
Proxies	O
also	O
allow	O
the	O
browser	O
to	O
make	O
web	O
requests	O
to	O
externally	O
hosted	O
content	O
on	O
behalf	O
of	O
a	O
website	O
when	O
cross-domain	B-Protocol
restrictions	I-Protocol
(	O
in	O
place	O
to	O
protect	O
websites	O
from	O
the	O
likes	O
of	O
data	O
theft	O
)	O
prohibit	O
the	O
browser	O
from	O
directly	O
accessing	O
the	O
outside	O
domains	O
.	O
</s>
<s>
Secondary	O
market	O
brokers	O
use	O
web	O
proxy	B-Application
servers	I-Application
to	O
circumvent	O
restrictions	O
on	O
online	O
purchase	O
of	O
limited	O
products	O
such	O
as	O
limited	O
sneakers	O
or	O
tickets	O
.	O
</s>
<s>
Web	O
proxies	O
forward	O
HTTP	B-Protocol
requests	I-Protocol
.	O
</s>
<s>
The	O
request	O
from	O
the	O
client	B-Protocol
is	O
the	O
same	O
as	O
a	O
regular	O
HTTP	B-Protocol
request	O
except	O
the	O
full	O
URL	O
is	O
passed	O
,	O
instead	O
of	O
just	O
the	O
path	O
.	O
</s>
<s>
This	O
request	O
is	O
sent	O
to	O
the	O
proxy	B-Application
server	I-Application
,	O
the	O
proxy	O
makes	O
the	O
request	O
specified	O
and	O
returns	O
the	O
response	O
.	O
</s>
<s>
Some	O
web	O
proxies	O
allow	O
the	O
HTTP	B-Protocol
CONNECT	O
method	O
to	O
set	O
up	O
forwarding	B-Protocol
of	O
arbitrary	O
data	O
through	O
the	O
connection	O
;	O
a	O
common	O
policy	O
is	O
to	O
only	O
forward	O
port	O
443	O
to	O
allow	O
HTTPS	B-Protocol
traffic	O
.	O
</s>
<s>
Examples	O
of	O
web	O
proxy	B-Application
servers	I-Application
include	O
Apache	B-Application
(	O
with	O
mod_proxy	O
or	O
Traffic	B-Language
Server	I-Language
)	O
,	O
HAProxy	B-Language
,	O
IIS	B-Application
configured	O
as	O
proxy	O
(	O
e.g.	O
,	O
with	O
Application	O
Request	O
Routing	O
)	O
,	O
Nginx	B-Operating_System
,	O
Privoxy	B-Language
,	O
Squid	B-Protocol
,	O
Varnish	B-Language
(	O
reverse	B-General_Concept
proxy	I-General_Concept
only	O
)	O
,	O
WinGate	B-Application
,	O
Ziproxy	B-Protocol
,	O
Tinyproxy	O
,	O
RabbIT	B-Algorithm
and	O
Polipo	B-Protocol
.	O
</s>
<s>
For	O
clients	O
,	O
the	O
problem	O
of	O
complex	O
or	O
multiple	O
proxy-servers	O
is	O
solved	O
by	O
a	O
client-server	O
Proxy	O
auto-config	O
protocol	O
(	O
PAC	B-Protocol
file	I-Protocol
)	O
.	O
</s>
<s>
SOCKS	B-Application
also	O
forwards	O
arbitrary	O
data	O
after	O
a	O
connection	O
phase	O
,	O
and	O
is	O
similar	O
to	O
HTTP	B-Protocol
CONNECT	O
in	O
web	O
proxies	O
.	O
</s>
<s>
Also	O
known	O
as	O
an	O
intercepting	O
proxy	O
,	O
inline	O
proxy	O
,	O
or	O
forced	O
proxy	O
,	O
a	O
transparent	O
proxy	O
intercepts	O
normal	O
application	B-Application
layer	I-Application
communication	O
without	O
requiring	O
any	O
special	O
client	B-Protocol
configuration	O
.	O
</s>
<s>
A	O
transparent	O
proxy	O
is	O
normally	O
located	O
between	O
the	O
client	B-Protocol
and	O
the	O
Internet	O
,	O
with	O
the	O
proxy	O
performing	O
some	O
of	O
the	O
functions	O
of	O
a	O
gateway	B-Application
or	O
router	B-Protocol
.	O
</s>
<s>
(	O
Hypertext	B-Protocol
Transfer	I-Protocol
Protocol	I-Protocol
—	O
HTTP/1.1	B-Protocol
)	O
offers	O
standard	O
definitions	O
:	O
</s>
<s>
"	O
A	O
'	O
transparent	O
proxy	O
 '	O
is	O
a	O
proxy	O
that	O
does	O
not	O
modify	O
the	O
request	O
or	O
response	O
beyond	O
what	O
is	O
required	O
for	O
proxy	O
authentication	B-Protocol
and	O
identification	O
"	O
.	O
</s>
<s>
TCP	B-Protocol
Intercept	O
is	O
a	O
traffic	O
filtering	O
security	O
feature	O
that	O
protects	O
TCP	B-Protocol
servers	O
from	O
TCP	B-Protocol
SYN	O
flood	O
attacks	O
,	O
which	O
are	O
a	O
type	O
of	O
denial-of-service	O
attack	O
.	O
</s>
<s>
TCP	B-Protocol
Intercept	O
is	O
available	O
for	O
IP	B-Protocol
traffic	O
only	O
.	O
</s>
<s>
In	O
2009	O
a	O
security	O
flaw	O
in	O
the	O
way	O
that	O
transparent	O
proxies	O
operate	O
was	O
published	O
by	O
Robert	B-Protocol
Auger	O
,	O
and	O
the	O
Computer	O
Emergency	O
Response	O
Team	O
issued	O
an	O
advisory	O
listing	O
dozens	O
of	O
affected	O
transparent	O
and	O
intercepting	B-Application
proxy	I-Application
servers	I-Application
.	O
</s>
<s>
Intercepting	O
proxies	O
are	O
commonly	O
used	O
in	O
businesses	O
to	O
enforce	O
acceptable	B-Application
use	I-Application
policy	I-Application
,	O
and	O
to	O
ease	O
administrative	O
overheads	O
since	O
no	O
client	B-Protocol
browser	O
configuration	O
is	O
required	O
.	O
</s>
<s>
This	O
second	O
reason	O
however	O
is	O
mitigated	O
by	O
features	O
such	O
as	O
Active	O
Directory	O
group	O
policy	O
,	O
or	O
DHCP	B-Protocol
and	O
automatic	O
proxy	O
detection	O
.	O
</s>
<s>
Intercepting	O
proxies	O
are	O
also	O
commonly	O
used	O
by	O
ISPs	O
in	O
some	O
countries	O
to	O
save	O
upstream	O
bandwidth	O
and	O
improve	O
customer	O
response	O
times	O
by	O
caching	B-General_Concept
.	O
</s>
<s>
The	O
diversion/interception	O
of	O
a	O
TCP	B-Protocol
connection	O
creates	O
several	O
issues	O
.	O
</s>
<s>
First	O
,	O
the	O
original	O
destination	O
IP	B-Protocol
and	O
port	O
must	O
somehow	O
be	O
communicated	O
to	O
the	O
proxy	O
.	O
</s>
<s>
This	O
is	O
not	O
always	O
possible	O
(	O
e.g.	O
,	O
where	O
the	O
gateway	B-Application
and	O
proxy	O
reside	O
on	O
different	O
hosts	O
)	O
.	O
</s>
<s>
This	O
problem	O
may	O
be	O
resolved	O
by	O
using	O
an	O
integrated	O
packet-level	O
and	O
application	O
level	O
appliance	O
or	O
software	O
which	O
is	O
then	O
able	O
to	O
communicate	O
this	O
information	O
between	O
the	O
packet	B-Protocol
handler	O
and	O
the	O
proxy	O
.	O
</s>
<s>
Intercepting	O
also	O
creates	O
problems	O
for	O
HTTP	B-Protocol
authentication	B-Protocol
,	O
especially	O
connection-oriented	O
authentication	B-Protocol
such	O
as	O
NTLM	O
,	O
as	O
the	O
client	B-Protocol
browser	O
believes	O
it	O
is	O
talking	O
to	O
a	O
server	B-Application
rather	O
than	O
a	O
proxy	O
.	O
</s>
<s>
This	O
can	O
cause	O
problems	O
where	O
an	O
intercepting	O
proxy	O
requires	O
authentication	B-Protocol
,	O
then	O
the	O
user	O
connects	O
to	O
a	O
site	O
that	O
also	O
requires	O
authentication	B-Protocol
.	O
</s>
<s>
Finally	O
,	O
intercepting	O
connections	O
can	O
cause	O
problems	O
for	O
HTTP	B-Protocol
caches	I-Protocol
,	O
as	O
some	O
requests	O
and	O
responses	O
become	O
uncacheable	O
by	O
a	O
shared	O
cache	B-Protocol
.	O
</s>
<s>
In	O
integrated	O
firewall/proxy	O
servers	O
where	O
the	O
router/firewall	O
is	O
on	O
the	O
same	O
host	O
as	O
the	O
proxy	O
,	O
communicating	O
original	O
destination	O
information	O
can	O
be	O
done	O
by	O
any	O
method	O
,	O
for	O
example	O
Microsoft	B-Application
TMG	I-Application
or	O
WinGate	B-Application
.	O
</s>
<s>
Interception	O
can	O
also	O
be	O
performed	O
using	O
Cisco	O
's	O
WCCP	B-Protocol
(	O
Web	B-Protocol
Cache	I-Protocol
Control	O
Protocol	O
)	O
.	O
</s>
<s>
This	O
proprietary	O
protocol	O
resides	O
on	O
the	O
router	B-Protocol
and	O
is	O
configured	O
from	O
the	O
cache	B-Protocol
,	O
allowing	O
the	O
cache	B-Protocol
to	O
determine	O
what	O
ports	O
and	O
traffic	O
is	O
sent	O
to	O
it	O
via	O
transparent	O
redirection	O
from	O
the	O
router	B-Protocol
.	O
</s>
<s>
This	O
redirection	O
can	O
occur	O
in	O
one	O
of	O
two	O
ways	O
:	O
GRE	B-Protocol
tunneling	I-Protocol
(	O
OSI	O
Layer	O
3	O
)	O
or	O
MAC	O
rewrites	O
(	O
OSI	O
Layer	O
2	O
)	O
.	O
</s>
<s>
Once	O
traffic	O
reaches	O
the	O
proxy	O
machine	O
itself	O
interception	O
is	O
commonly	O
performed	O
with	O
NAT	O
(	O
Network	B-Protocol
Address	I-Protocol
Translation	I-Protocol
)	O
.	O
</s>
<s>
Such	O
setups	O
are	O
invisible	O
to	O
the	O
client	B-Protocol
browser	O
,	O
but	O
leave	O
the	O
proxy	O
visible	O
to	O
the	O
web	O
server	B-Application
and	O
other	O
devices	O
on	O
the	O
internet	O
side	O
of	O
the	O
proxy	O
.	O
</s>
<s>
Recent	O
Linux	O
and	O
some	O
BSD	O
releases	O
provide	O
TPROXY	O
(	O
transparent	O
proxy	O
)	O
which	O
performs	O
IP-level	O
(	O
OSI	O
Layer	O
3	O
)	O
transparent	O
interception	O
and	O
spoofing	O
of	O
outbound	O
traffic	O
,	O
hiding	O
the	O
proxy	B-Application
IP	I-Application
address	I-Application
from	O
other	O
network	O
devices	O
.	O
</s>
<s>
Several	O
methods	O
may	O
be	O
used	O
to	O
detect	O
the	O
presence	O
of	O
an	O
intercepting	B-Application
proxy	I-Application
server	I-Application
:	O
</s>
<s>
By	O
comparing	O
the	O
client	B-Protocol
's	O
external	O
IP	B-Protocol
address	I-Protocol
to	O
the	O
address	O
seen	O
by	O
an	O
external	O
web	O
server	B-Application
,	O
or	O
sometimes	O
by	O
examining	O
the	O
HTTP	B-Protocol
headers	I-Protocol
received	O
by	O
a	O
server	B-Application
.	O
</s>
<s>
A	O
number	O
of	O
sites	O
have	O
been	O
created	O
to	O
address	O
this	O
issue	O
,	O
by	O
reporting	O
the	O
user	O
's	O
IP	B-Protocol
address	I-Protocol
as	O
seen	O
by	O
the	O
site	O
back	O
to	O
the	O
user	O
on	O
a	O
web	O
page	O
.	O
</s>
<s>
Google	O
also	O
returns	O
the	O
IP	B-Protocol
address	I-Protocol
as	O
seen	O
by	O
the	O
page	O
if	O
the	O
user	O
searches	O
for	O
"	O
IP	B-Protocol
"	O
.	O
</s>
<s>
By	O
comparing	O
the	O
result	O
of	O
online	O
IP	B-Protocol
checkers	O
when	O
accessed	O
using	O
HTTPS	B-Protocol
vs	O
HTTP	B-Protocol
,	O
as	O
most	O
intercepting	O
proxies	O
do	O
not	O
intercept	O
SSL	O
.	O
</s>
<s>
By	O
comparing	O
the	O
sequence	O
of	O
network	O
hops	O
reported	O
by	O
a	O
tool	O
such	O
as	O
traceroute	B-Protocol
for	O
a	O
proxied	O
protocol	O
such	O
as	O
HTTP	B-Protocol
(	O
port	O
80	O
)	O
with	O
that	O
for	O
a	O
non-proxied	O
protocol	O
such	O
as	O
SMTP	O
(	O
port	O
25	O
)	O
.	O
</s>
<s>
By	O
attempting	O
to	O
make	O
a	O
connection	O
to	O
an	O
IP	B-Protocol
address	I-Protocol
at	O
which	O
there	O
is	O
known	O
to	O
be	O
no	O
server	B-Application
.	O
</s>
<s>
When	O
the	O
proxy	O
finds	O
no	O
server	B-Application
to	O
accept	O
the	O
connection	O
it	O
may	O
return	O
an	O
error	O
message	O
or	O
simply	O
close	O
the	O
connection	O
to	O
the	O
client	B-Protocol
.	O
</s>
<s>
For	O
example	O
,	O
most	O
web	O
browsers	O
will	O
generate	O
a	O
browser	O
created	O
error	O
page	O
in	O
the	O
case	O
where	O
they	O
cannot	O
connect	O
to	O
an	O
HTTP	B-Protocol
server	B-Application
but	O
will	O
return	O
a	O
different	O
error	O
in	O
the	O
case	O
where	O
the	O
connection	O
is	O
accepted	O
and	O
then	O
closed	O
.	O
</s>
<s>
By	O
serving	O
the	O
end-user	O
specially	O
programmed	O
Adobe	O
Flash	O
SWF	O
applications	O
or	O
Sun	O
Java	O
applets	O
that	O
send	O
HTTP	B-Protocol
calls	O
back	O
to	O
their	O
server	B-Application
.	O
</s>
<s>
A	O
CGI	B-Language
web	O
proxy	O
accepts	O
target	O
URLs	O
using	O
a	O
Web	B-General_Concept
form	I-General_Concept
in	O
the	O
user	O
's	O
browser	O
window	O
,	O
processes	O
the	O
request	O
,	O
and	O
returns	O
the	O
results	O
to	O
the	O
user	O
's	O
browser	O
.	O
</s>
<s>
The	O
first	O
recorded	O
CGI	B-Language
proxy	O
,	O
named	O
"	O
rover	O
"	O
at	O
the	O
time	O
but	O
renamed	O
in	O
1998	O
to	O
"	O
CGIProxy	B-Language
"	O
,	O
was	O
developed	O
by	O
American	O
computer	O
scientist	O
James	O
Marshall	O
in	O
early	O
1996	O
for	O
an	O
article	O
in	O
"	O
Unix	O
Review	O
"	O
by	O
Rich	O
Morin	O
.	O
</s>
<s>
The	O
majority	O
of	O
CGI	B-Language
proxies	O
are	O
powered	O
by	O
one	O
of	O
CGIProxy	B-Language
(	O
written	O
in	O
the	O
Perl	B-Language
language	I-Language
)	O
,	O
Glype	O
(	O
written	O
in	O
the	O
PHP	B-Application
language	I-Application
)	O
,	O
or	O
PHProxy	O
(	O
written	O
in	O
the	O
PHP	B-Application
language	I-Application
)	O
.	O
</s>
<s>
As	O
of	O
April	O
2016	O
,	O
CGIProxy	B-Language
has	O
received	O
about	O
2	O
million	O
downloads	O
,	O
Glype	O
has	O
received	O
almost	O
a	O
million	O
downloads	O
,	O
whilst	O
PHProxy	O
still	O
receives	O
hundreds	O
of	O
downloads	O
per	O
week	O
.	O
</s>
<s>
Despite	O
waning	O
in	O
popularity	O
due	O
to	O
VPNs	B-Application
and	O
other	O
privacy	O
methods	O
,	O
there	O
are	O
still	O
a	O
few	O
hundred	O
CGI	B-Language
proxies	O
online	O
.	O
</s>
<s>
Some	O
CGI	B-Language
proxies	O
were	O
set	O
up	O
for	O
purposes	O
such	O
as	O
making	O
websites	O
more	O
accessible	O
to	O
disabled	O
people	O
,	O
but	O
have	O
since	O
been	O
shut	O
down	O
due	O
to	O
excessive	O
traffic	O
,	O
usually	O
caused	O
by	O
a	O
third	B-General_Concept
party	I-General_Concept
advertising	I-General_Concept
the	I-General_Concept
service	I-General_Concept
as	O
a	O
means	O
to	O
bypass	O
local	O
filtering	O
.	O
</s>
<s>
A	O
suffix	O
proxy	O
allows	O
a	O
user	O
to	O
access	O
web	O
content	O
by	O
appending	O
the	O
name	O
of	O
the	O
proxy	B-Application
server	I-Application
to	O
the	O
URL	O
of	O
the	O
requested	O
content	O
(	O
e.g.	O
</s>
<s>
Suffix	O
proxy	B-Application
servers	I-Application
are	O
easier	O
to	O
use	O
than	O
regular	O
proxy	B-Application
servers	I-Application
but	O
they	O
do	O
not	O
offer	O
high	O
levels	O
of	O
anonymity	O
and	O
their	O
primary	O
use	O
is	O
for	O
bypassing	O
web	B-Protocol
filters	I-Protocol
.	O
</s>
<s>
However	O
,	O
this	O
is	O
rarely	O
used	O
due	O
to	O
more	O
advanced	O
web	B-Protocol
filters	I-Protocol
.	O
</s>
<s>
Tor	B-Application
is	O
a	O
system	O
intended	O
to	O
provide	O
online	O
anonymity	O
.	O
</s>
<s>
Tor	B-Application
client	B-Protocol
software	I-Protocol
routes	O
Internet	O
traffic	O
through	O
a	O
worldwide	O
volunteer	O
network	O
of	O
servers	O
for	O
concealing	O
a	O
user	O
's	O
computer	O
location	O
or	O
usage	O
from	O
someone	O
conducting	O
network	O
surveillance	O
or	O
traffic	O
analysis	O
.	O
</s>
<s>
Using	O
Tor	B-Application
makes	O
tracing	O
Internet	O
activity	O
more	O
difficult	O
,	O
and	O
is	O
intended	O
to	O
protect	O
users	O
 '	O
personal	O
freedom	O
and	O
their	O
online	O
privacy	O
.	O
</s>
<s>
"	O
Onion	B-Protocol
routing	I-Protocol
"	O
refers	O
to	O
the	O
layered	O
nature	O
of	O
the	O
encryption	O
service	O
:	O
The	O
original	O
data	O
are	O
encrypted	O
and	O
re-encrypted	O
multiple	O
times	O
,	O
then	O
sent	O
through	O
successive	O
Tor	B-Application
relays	O
,	O
each	O
one	O
of	O
which	O
decrypts	O
a	O
"	O
layer	O
"	O
of	O
encryption	O
before	O
passing	O
the	O
data	O
on	O
to	O
the	O
next	O
relay	O
and	O
ultimately	O
the	O
destination	O
.	O
</s>
<s>
The	O
I2P	B-Protocol
anonymous	I-Protocol
network	I-Protocol
( 	O
 '	O
I2P	B-Protocol
 '	O
)	O
is	O
a	O
proxy	O
network	O
aiming	O
at	O
online	O
anonymity	O
.	O
</s>
<s>
It	O
implements	O
garlic	B-Protocol
routing	I-Protocol
,	O
which	O
is	O
an	O
enhancement	O
of	O
Tor	B-Application
's	O
onion	B-Protocol
routing	I-Protocol
.	O
</s>
<s>
I2P	B-Protocol
is	O
fully	O
distributed	O
and	O
works	O
by	O
encrypting	O
all	O
communications	O
in	O
various	O
layers	O
and	O
relaying	O
them	O
through	O
a	O
network	O
of	O
routers	B-Protocol
run	O
by	O
volunteers	O
in	O
various	O
locations	O
.	O
</s>
<s>
By	O
keeping	O
the	O
source	O
of	O
the	O
information	O
hidden	O
,	O
I2P	B-Protocol
offers	O
censorship	O
resistance	O
.	O
</s>
<s>
The	O
goals	O
of	O
I2P	B-Protocol
are	O
to	O
protect	O
users	O
 '	O
personal	O
freedom	O
,	O
privacy	O
,	O
and	O
ability	O
to	O
conduct	O
confidential	O
business	O
.	O
</s>
<s>
Each	O
user	O
of	O
I2P	B-Protocol
runs	O
an	O
I2P	B-Protocol
router	B-Protocol
on	O
their	O
computer	O
(	O
node	O
)	O
.	O
</s>
<s>
The	O
I2P	B-Protocol
router	B-Protocol
takes	O
care	O
of	O
finding	O
other	O
peers	O
and	O
building	O
anonymizing	O
tunnels	O
through	O
them	O
.	O
</s>
<s>
I2P	B-Protocol
provides	O
proxies	O
for	O
all	O
protocols	O
(	O
HTTP	B-Protocol
,	O
IRC	B-Protocol
,	O
SOCKS	B-Application
,	O
...	O
)	O
.	O
</s>
<s>
Network	B-Protocol
address	I-Protocol
translation	I-Protocol
(	O
NAT	O
)	O
is	O
similar	O
to	O
a	O
proxy	O
but	O
operates	O
in	O
layer	O
3	O
.	O
</s>
<s>
In	O
the	O
client	B-Protocol
configuration	O
of	O
layer-3	O
NAT	O
,	O
configuring	O
the	O
gateway	B-Application
is	O
sufficient	O
.	O
</s>
<s>
However	O
,	O
for	O
the	O
client	B-Protocol
configuration	O
of	O
a	O
layer	O
7	O
proxy	O
,	O
the	O
destination	O
of	O
the	O
packets	B-Protocol
that	O
the	O
client	B-Protocol
generates	O
must	O
always	O
be	O
the	O
proxy	B-Application
server	I-Application
(	O
layer	O
7	O
)	O
,	O
then	O
the	O
proxy	B-Application
server	I-Application
reads	O
each	O
packet	B-Protocol
and	O
finds	O
out	O
the	O
true	O
destination	O
.	O
</s>
<s>
As	O
we	O
compare	O
these	O
two	O
technologies	O
,	O
we	O
might	O
encounter	O
a	O
terminology	O
known	O
as	O
'	O
transparent	B-Protocol
firewall	I-Protocol
 '	O
.	O
</s>
<s>
Transparent	B-Protocol
firewall	I-Protocol
means	O
that	O
the	O
proxy	O
uses	O
the	O
layer-7	O
proxy	O
advantages	O
without	O
the	O
knowledge	O
of	O
the	O
client	B-Protocol
.	O
</s>
<s>
The	O
client	B-Protocol
presumes	O
that	O
the	O
gateway	B-Application
is	O
a	O
NAT	O
in	O
layer	O
3	O
,	O
and	O
it	O
does	O
not	O
have	O
any	O
idea	O
about	O
the	O
inside	O
of	O
the	O
packet	B-Protocol
,	O
but	O
through	O
this	O
method	O
,	O
the	O
layer-3	O
packets	B-Protocol
are	O
sent	O
to	O
the	O
layer-7	O
proxy	O
for	O
investigation	O
.	O
</s>
<s>
A	O
DNS	B-Protocol
proxy	B-Application
server	I-Application
takes	O
DNS	B-Protocol
queries	I-Protocol
from	O
a	O
(	O
usually	O
local	O
)	O
network	O
and	O
forwards	O
them	O
to	O
an	O
Internet	O
Domain	O
Name	O
Server	B-Application
.	O
</s>
<s>
It	O
may	O
also	O
cache	B-Protocol
DNS	B-Protocol
records	O
.	O
</s>
<s>
Some	O
client	B-Protocol
programs	I-Protocol
"	O
SOCKS-ify	O
"	O
requests	O
,	O
which	O
allows	O
adaptation	O
of	O
any	O
networked	O
software	O
to	O
connect	O
to	O
external	O
networks	O
via	O
certain	O
types	O
of	O
proxy	B-Application
servers	I-Application
(	O
mostly	O
SOCKS	B-Application
)	O
.	O
</s>
<s>
A	O
residential	O
proxy	O
is	O
an	O
intermediary	O
that	O
uses	O
a	O
real	O
IP	B-Protocol
address	I-Protocol
provided	O
by	O
an	O
Internet	O
Service	O
Provider	O
(	O
ISP	O
)	O
with	O
physical	O
devices	O
such	O
as	O
mobiles	O
and	O
computers	B-Device
of	I-Device
end-users	I-Device
.	O
</s>
<s>
Instead	O
of	O
connecting	O
directly	O
to	O
a	O
server	B-Application
,	O
residential	O
proxy	O
users	O
connect	O
to	O
the	O
target	O
through	O
residential	O
IP	B-Protocol
addresses	I-Protocol
.	O
</s>
<s>
Any	O
residential	O
proxy	O
can	O
send	O
any	O
number	O
of	O
concurrent	O
requests	O
and	O
IP	B-Protocol
addresses	I-Protocol
are	O
directly	O
related	O
to	O
a	O
specific	O
region	O
.	O
</s>
<s>
Unlike	O
regular	O
residential	O
proxies	O
,	O
which	O
hide	O
user	O
's	O
real	O
IP	B-Protocol
address	I-Protocol
behind	O
another	O
IP	B-Protocol
address	I-Protocol
,	O
rotating	O
residential	O
proxies	O
,	O
also	O
known	O
as	O
backconnect	O
proxies	O
,	O
conceal	O
user	O
's	O
real	O
IP	B-Protocol
address	I-Protocol
behind	O
a	O
pool	O
of	O
proxies	O
.	O
</s>
