<s>
Internet	B-Protocol
Small	I-Protocol
Computer	I-Protocol
Systems	I-Protocol
Interface	I-Protocol
or	O
iSCSI	B-Protocol
(	O
)	O
is	O
an	O
Internet	O
Protocol-based	O
storage	O
networking	O
standard	O
for	O
linking	O
data	O
storage	O
facilities	O
.	O
</s>
<s>
iSCSI	B-Protocol
provides	O
block-level	B-General_Concept
access	I-General_Concept
to	O
storage	O
devices	O
by	O
carrying	O
SCSI	B-Architecture
commands	O
over	O
a	O
TCP/IP	B-Protocol
network	I-Protocol
.	O
</s>
<s>
iSCSI	B-Protocol
facilitates	O
data	O
transfers	O
over	O
intranets	B-General_Concept
and	O
to	O
manage	O
storage	O
over	O
long	O
distances	O
.	O
</s>
<s>
It	O
can	O
be	O
used	O
to	O
transmit	O
data	O
over	O
local	B-General_Concept
area	I-General_Concept
networks	I-General_Concept
(	O
LANs	B-General_Concept
)	O
,	O
wide	O
area	O
networks	O
(	O
WANs	O
)	O
,	O
or	O
the	O
Internet	O
and	O
can	O
enable	O
location-independent	O
data	O
storage	O
and	O
retrieval	O
.	O
</s>
<s>
The	O
protocol	O
allows	O
clients	O
(	O
called	O
initiators	O
)	O
to	O
send	O
SCSI	B-Architecture
commands	O
(	O
CDBs	O
)	O
to	O
storage	O
devices	O
(	O
targets	O
)	O
on	O
remote	O
servers	O
.	O
</s>
<s>
It	O
is	O
a	O
storage	O
area	O
network	O
(	O
SAN	O
)	O
protocol	O
,	O
allowing	O
organizations	O
to	O
consolidate	O
storage	O
into	O
storage	B-General_Concept
arrays	I-General_Concept
while	O
providing	O
clients	O
(	O
such	O
as	O
database	O
and	O
web	O
servers	O
)	O
with	O
the	O
illusion	O
of	O
locally	O
attached	O
SCSI	B-Architecture
disks	O
.	O
</s>
<s>
It	O
mainly	O
competes	O
with	O
Fibre	B-Architecture
Channel	I-Architecture
,	O
but	O
unlike	O
traditional	O
Fibre	B-Architecture
Channel	I-Architecture
which	O
usually	O
requires	O
dedicated	O
cabling	O
,	O
iSCSI	B-Protocol
can	O
be	O
run	O
over	O
long	O
distances	O
using	O
existing	O
network	O
infrastructure	O
.	O
</s>
<s>
iSCSI	B-Protocol
was	O
pioneered	O
by	O
IBM	O
and	O
Cisco	O
in	O
1998	O
and	O
submitted	O
as	O
a	O
draft	O
standard	O
in	O
March	O
2000	O
.	O
</s>
<s>
In	O
essence	O
,	O
iSCSI	B-Protocol
allows	O
two	O
hosts	O
to	O
negotiate	O
and	O
then	O
exchange	O
SCSI	B-Architecture
commands	O
using	O
Internet	B-Protocol
Protocol	I-Protocol
(	O
IP	O
)	O
networks	O
.	O
</s>
<s>
By	O
doing	O
this	O
,	O
iSCSI	B-Protocol
takes	O
a	O
popular	O
high-performance	O
local	O
storage	O
bus	O
and	O
emulates	O
it	O
over	O
a	O
wide	O
range	O
of	O
networks	O
,	O
creating	O
a	O
storage	O
area	O
network	O
(	O
SAN	O
)	O
.	O
</s>
<s>
Unlike	O
some	O
SAN	O
protocols	O
,	O
iSCSI	B-Protocol
requires	O
no	O
dedicated	O
cabling	O
;	O
it	O
can	O
be	O
run	O
over	O
existing	O
IP	O
infrastructure	O
.	O
</s>
<s>
As	O
a	O
result	O
,	O
iSCSI	B-Protocol
is	O
often	O
seen	O
as	O
a	O
low-cost	O
alternative	O
to	O
Fibre	B-Architecture
Channel	I-Architecture
,	O
which	O
requires	O
dedicated	O
infrastructure	O
except	O
in	O
its	O
FCoE	B-Protocol
(	O
Fibre	B-Protocol
Channel	I-Protocol
over	I-Protocol
Ethernet	I-Protocol
)	O
form	O
.	O
</s>
<s>
However	O
,	O
the	O
performance	O
of	O
an	O
iSCSI	B-Protocol
SAN	O
deployment	O
can	O
be	O
severely	O
degraded	O
if	O
not	O
operated	O
on	O
a	O
dedicated	O
network	O
or	O
subnet	O
(	O
LAN	B-General_Concept
or	O
VLAN	B-General_Concept
)	O
,	O
due	O
to	O
competition	O
for	O
a	O
fixed	O
amount	O
of	O
bandwidth	O
.	O
</s>
<s>
Although	O
iSCSI	B-Protocol
can	O
communicate	O
with	O
arbitrary	O
types	O
of	O
SCSI	B-Architecture
devices	O
,	O
system	O
administrators	O
almost	O
always	O
use	O
it	O
to	O
allow	O
servers	O
(	O
such	O
as	O
database	O
servers	O
)	O
to	O
access	O
disk	O
volumes	O
on	O
storage	B-General_Concept
arrays	I-General_Concept
.	O
</s>
<s>
iSCSI	B-Protocol
SANs	O
often	O
have	O
one	O
of	O
two	O
objectives	O
:	O
</s>
<s>
In	O
particular	O
,	O
iSCSI	B-Protocol
SANs	O
allow	O
entire	O
disk	B-General_Concept
arrays	I-General_Concept
to	O
be	O
migrated	O
across	O
a	O
WAN	O
with	O
minimal	O
configuration	O
changes	O
,	O
in	O
effect	O
making	O
storage	O
"	O
routable	O
"	O
in	O
the	O
same	O
manner	O
as	O
network	O
traffic	O
.	O
</s>
<s>
An	O
initiator	O
functions	O
as	O
an	O
iSCSI	B-Protocol
client	O
.	O
</s>
<s>
An	O
initiator	O
typically	O
serves	O
the	O
same	O
purpose	O
to	O
a	O
computer	O
as	O
a	O
SCSI	B-Architecture
bus	O
adapter	O
would	O
,	O
except	O
that	O
,	O
instead	O
of	O
physically	O
cabling	O
SCSI	B-Architecture
devices	O
(	O
like	O
hard	O
drives	O
and	O
tape	O
changers	O
)	O
,	O
an	O
iSCSI	B-Protocol
initiator	O
sends	O
SCSI	B-Architecture
commands	O
over	O
an	O
IP	B-Protocol
network	I-Protocol
.	O
</s>
<s>
A	O
software	O
initiator	O
uses	O
code	O
to	O
implement	O
iSCSI	B-Protocol
.	O
</s>
<s>
Typically	O
,	O
this	O
happens	O
in	O
a	O
kernel-resident	B-Operating_System
device	O
driver	O
that	O
uses	O
the	O
existing	O
network	B-Protocol
card	I-Protocol
(	O
NIC	O
)	O
and	O
network	B-Protocol
stack	I-Protocol
to	O
emulate	O
SCSI	B-Architecture
devices	O
for	O
a	O
computer	O
by	O
speaking	O
the	O
iSCSI	B-Protocol
protocol	O
.	O
</s>
<s>
Software	O
initiators	O
are	O
available	O
for	O
most	O
popular	O
operating	O
systems	O
and	O
are	O
the	O
most	O
common	O
method	O
of	O
deploying	O
iSCSI	B-Protocol
.	O
</s>
<s>
A	O
hardware	O
initiator	O
uses	O
dedicated	O
hardware	O
,	O
typically	O
in	O
combination	O
with	O
firmware	B-Application
running	O
on	O
that	O
hardware	O
,	O
to	O
implement	O
iSCSI	B-Protocol
.	O
</s>
<s>
A	O
hardware	O
initiator	O
mitigates	O
the	O
overhead	O
of	O
iSCSI	B-Protocol
and	O
TCP	B-Protocol
processing	O
and	O
Ethernet	B-Application
interrupts	I-Application
,	O
and	O
therefore	O
may	O
improve	O
the	O
performance	O
of	O
servers	O
that	O
use	O
iSCSI	B-Protocol
.	O
</s>
<s>
An	O
iSCSI	B-Protocol
host	B-Architecture
bus	I-Architecture
adapter	I-Architecture
(	O
more	O
commonly	O
,	O
HBA	O
)	O
implements	O
a	O
hardware	O
initiator	O
.	O
</s>
<s>
A	O
typical	O
HBA	O
is	O
packaged	O
as	O
a	O
combination	O
of	O
a	O
Gigabit	O
(	O
or	O
10	O
Gigabit	O
)	O
Ethernet	O
network	B-Protocol
interface	I-Protocol
controller	I-Protocol
,	O
some	O
kind	O
of	O
TCP/IP	B-Protocol
offload	I-Protocol
engine	I-Protocol
(	O
TOE	O
)	O
technology	O
and	O
a	O
SCSI	B-Architecture
bus	O
adapter	O
,	O
which	O
is	O
how	O
it	O
appears	O
to	O
the	O
operating	O
system	O
.	O
</s>
<s>
An	O
iSCSI	B-Protocol
HBA	O
can	O
include	O
PCI	B-Protocol
option	B-Device
ROM	I-Device
to	O
allow	O
booting	B-Operating_System
from	O
an	O
iSCSI	B-Protocol
SAN	O
.	O
</s>
<s>
An	O
iSCSI	B-Protocol
offload	O
engine	O
,	O
or	O
iSOE	O
card	O
,	O
offers	O
an	O
alternative	O
to	O
a	O
full	O
iSCSI	B-Protocol
HBA	O
.	O
</s>
<s>
An	O
iSOE	O
"	O
offloads	O
"	O
the	O
iSCSI	B-Protocol
initiator	O
operations	O
for	O
this	O
particular	O
network	O
interface	O
from	O
the	O
host	O
processor	O
,	O
freeing	O
up	O
CPU	O
cycles	O
for	O
the	O
main	O
host	O
applications	O
.	O
</s>
<s>
iSCSI	B-Protocol
HBAs	O
or	O
iSOEs	O
are	O
used	O
when	O
the	O
additional	O
performance	O
enhancement	O
justifies	O
the	O
additional	O
expense	O
of	O
using	O
an	O
HBA	O
for	O
iSCSI	B-Protocol
,	O
rather	O
than	O
using	O
a	O
software-based	O
iSCSI	B-Protocol
client	O
(	O
initiator	O
)	O
.	O
</s>
<s>
iSOE	O
may	O
be	O
implemented	O
with	O
additional	O
services	O
such	O
as	O
TCP	B-Protocol
offload	I-Protocol
engine	I-Protocol
(	O
TOE	O
)	O
to	O
further	O
reduce	O
host	O
server	O
CPU	O
usage	O
.	O
</s>
<s>
The	O
iSCSI	B-Protocol
specification	O
refers	O
to	O
a	O
storage	O
resource	O
located	O
on	O
an	O
iSCSI	B-Protocol
server	O
(	O
more	O
generally	O
,	O
one	O
of	O
potentially	O
many	O
instances	O
of	O
iSCSI	B-Protocol
storage	O
nodes	O
running	O
on	O
that	O
server	O
)	O
as	O
a	O
target	B-Application
.	O
</s>
<s>
An	O
iSCSI	B-Protocol
target	B-Application
is	O
often	O
a	O
dedicated	O
network-connected	O
hard	O
disk	O
storage	B-General_Concept
device	I-General_Concept
,	O
but	O
may	O
also	O
be	O
a	O
general-purpose	O
computer	O
,	O
since	O
as	O
with	O
initiators	O
,	O
software	O
to	O
provide	O
an	O
iSCSI	B-Protocol
target	B-Application
is	O
available	O
for	O
most	O
mainstream	O
operating	O
systems	O
.	O
</s>
<s>
Common	O
deployment	O
scenarios	O
for	O
an	O
iSCSI	B-Protocol
target	B-Application
include	O
:	O
</s>
<s>
In	O
a	O
data	O
center	O
or	O
enterprise	O
environment	O
,	O
an	O
iSCSI	B-Protocol
target	B-Application
often	O
resides	O
in	O
a	O
large	O
storage	B-General_Concept
array	I-General_Concept
.	O
</s>
<s>
These	O
arrays	O
can	O
be	O
in	O
the	O
form	O
of	O
commodity	O
hardware	O
with	O
free-software-based	O
iSCSI	B-Protocol
implementations	O
,	O
or	O
as	O
commercial	O
products	O
such	O
as	O
in	O
,	O
CloudByte	O
,	O
StorTrends	O
,	O
Pure	B-General_Concept
Storage	I-General_Concept
,	O
HP	B-Device
StorageWorks	I-Device
,	O
EqualLogic	O
,	O
Tegile	O
Systems	O
,	O
Nimble	O
storage	O
,	O
Reduxio	O
,	O
IBM	B-Device
Storwize	I-Device
family	I-Device
,	O
Isilon	O
,	O
NetApp	B-Operating_System
filer	I-Operating_System
,	O
Dell	O
EMC	O
,	O
Kaminario	O
,	O
NS-series	O
,	O
CX4	O
,	O
VNX	O
,	O
VNXe	O
,	O
VMAX	O
,	O
Hitachi	O
Data	O
Systems	O
HNAS	O
,	O
or	O
Pivot3	O
vSTAC	O
.	O
</s>
<s>
A	O
storage	B-General_Concept
array	I-General_Concept
usually	O
provides	O
distinct	O
iSCSI	B-Protocol
targets	O
for	O
numerous	O
clients	O
.	O
</s>
<s>
Nearly	O
all	O
modern	O
mainstream	O
server	O
operating	O
systems	O
(	O
such	O
as	O
BSD	B-Operating_System
,	O
Linux	B-Application
,	O
Solaris	B-Application
or	O
Windows	B-Device
Server	I-Device
)	O
can	O
provide	O
iSCSI	B-Protocol
target	B-Application
functionality	O
,	O
either	O
as	O
a	O
built-in	O
feature	O
or	O
with	O
supplemental	O
software	O
.	O
</s>
<s>
Some	O
specific-purpose	O
operating	O
systems	O
implement	O
iSCSI	B-Protocol
target	B-Application
support	O
.	O
</s>
<s>
In	O
SCSI	B-Architecture
terminology	O
,	O
LU	O
stands	O
for	O
logical	O
unit	O
,	O
which	O
is	O
specified	O
by	O
a	O
unique	O
logical	O
unit	O
number	O
.	O
</s>
<s>
A	O
LUN	O
represents	O
an	O
individually	O
addressable	O
(	O
logical	O
)	O
SCSI	B-Architecture
device	O
that	O
is	O
part	O
of	O
a	O
physical	O
SCSI	B-Architecture
device	O
(	O
target	B-Application
)	O
.	O
</s>
<s>
In	O
an	O
iSCSI	B-Protocol
environment	O
,	O
LUNs	O
are	O
essentially	O
numbered	O
disk	O
drives	O
.	O
</s>
<s>
An	O
initiator	O
negotiates	O
with	O
a	O
target	B-Application
to	O
establish	O
connectivity	O
to	O
a	O
LUN	O
;	O
the	O
result	O
is	O
an	O
iSCSI	B-Protocol
connection	O
that	O
emulates	O
a	O
connection	O
to	O
a	O
SCSI	B-Architecture
hard	O
disk	O
.	O
</s>
<s>
Initiators	O
treat	O
iSCSI	B-Protocol
LUNs	O
the	O
same	O
way	O
as	O
they	O
would	O
a	O
raw	O
SCSI	B-Architecture
or	O
IDE	O
hard	O
drive	O
;	O
for	O
instance	O
,	O
rather	O
than	O
mounting	O
remote	O
directories	O
as	O
would	O
be	O
done	O
in	O
NFS	B-Protocol
or	O
CIFS	B-Operating_System
environments	O
,	O
iSCSI	B-Protocol
systems	O
format	O
and	O
directly	O
manage	O
filesystems	O
on	O
iSCSI	B-Protocol
LUNs	O
.	O
</s>
<s>
In	O
enterprise	O
deployments	O
,	O
LUNs	O
usually	O
represent	O
subsets	O
of	O
large	O
RAID	B-Architecture
disk	B-General_Concept
arrays	I-General_Concept
,	O
often	O
allocated	O
one	O
per	O
client	O
.	O
</s>
<s>
iSCSI	B-Protocol
imposes	O
no	O
rules	O
or	O
restrictions	O
on	O
multiple	O
computers	O
sharing	O
individual	O
LUNs	O
;	O
it	O
leaves	O
shared	O
access	O
to	O
a	O
single	O
underlying	O
filesystem	O
as	O
a	O
task	O
for	O
the	O
operating	O
system	O
.	O
</s>
<s>
For	O
general	O
data	O
storage	O
on	O
an	O
already-booted	O
computer	O
,	O
any	O
type	O
of	O
generic	O
network	O
interface	O
may	O
be	O
used	O
to	O
access	O
iSCSI	B-Protocol
devices	O
.	O
</s>
<s>
However	O
,	O
a	O
generic	O
consumer-grade	O
network	O
interface	O
is	O
not	O
able	O
to	O
boot	B-Operating_System
a	O
diskless	O
computer	O
from	O
a	O
remote	O
iSCSI	B-Protocol
data	O
source	O
.	O
</s>
<s>
Instead	O
,	O
it	O
is	O
commonplace	O
for	O
a	O
server	O
to	O
load	O
its	O
initial	O
operating	O
system	O
from	O
a	O
TFTP	B-Device
server	O
or	O
local	O
boot	B-Operating_System
device	O
,	O
and	O
then	O
use	O
iSCSI	B-Protocol
for	O
data	O
storage	O
once	O
booting	B-Operating_System
from	O
the	O
local	O
device	O
has	O
finished	O
.	O
</s>
<s>
A	O
separate	O
DHCP	B-Protocol
server	I-Protocol
may	O
be	O
configured	O
to	O
assist	O
interfaces	O
equipped	O
with	O
network	B-Device
boot	I-Device
capability	O
to	O
be	O
able	O
to	O
boot	B-Operating_System
over	O
iSCSI	B-Protocol
.	O
</s>
<s>
In	O
this	O
case	O
,	O
the	O
network	O
interface	O
looks	O
for	O
a	O
DHCP	B-Protocol
server	I-Protocol
offering	O
a	O
PXE	B-Device
or	O
bootp	B-Device
boot	B-Operating_System
image	O
.	O
</s>
<s>
This	O
is	O
used	O
to	O
kick	O
off	O
the	O
iSCSI	B-Protocol
remote	O
boot	B-Operating_System
process	I-Operating_System
,	O
using	O
the	O
booting	B-Operating_System
network	O
interface	O
's	O
MAC	O
address	O
to	O
direct	O
the	O
computer	O
to	O
the	O
correct	O
iSCSI	B-Protocol
boot	B-Operating_System
target	B-Application
.	O
</s>
<s>
One	O
can	O
then	O
use	O
a	O
software-only	O
approach	O
to	O
load	O
a	O
small	O
boot	B-Operating_System
program	I-Operating_System
which	O
can	O
in	O
turn	O
mount	O
a	O
remote	O
iSCSI	B-Protocol
target	B-Application
as	O
if	O
it	O
was	O
a	O
local	O
SCSI	B-Architecture
drive	O
and	O
then	O
fire	O
the	O
boot	B-Operating_System
process	I-Operating_System
from	O
said	O
iSCSI	B-Protocol
target	B-Application
.	O
</s>
<s>
This	O
can	O
be	O
achieved	O
using	O
an	O
existing	O
Preboot	B-Device
Execution	I-Device
Environment	I-Device
(	O
PXE	B-Device
)	O
boot	B-Operating_System
ROM	O
,	O
which	O
is	O
available	O
on	O
many	O
wired	O
Ethernet	B-Protocol
adapters	I-Protocol
.	O
</s>
<s>
The	O
boot	B-Operating_System
code	O
can	O
also	O
be	O
loaded	O
from	O
CD/DVD	O
,	O
floppy	O
disk	O
(	O
or	O
floppy	O
disk	O
image	O
)	O
and	O
USB	O
storage	O
,	O
or	O
it	O
can	O
replace	O
existing	O
PXE	B-Device
boot	B-Operating_System
code	O
on	O
adapters	O
that	O
can	O
be	O
re-flashed	O
.	O
</s>
<s>
The	O
most	O
popular	O
free	B-Application
software	I-Application
to	O
offer	O
iSCSI	B-Protocol
boot	B-Operating_System
support	O
is	O
iPXE	B-Device
.	O
</s>
<s>
Most	O
Intel	O
Ethernet	O
controllers	O
for	O
servers	O
support	O
iSCSI	B-Protocol
boot	B-Operating_System
.	O
</s>
<s>
iSCSI	B-Protocol
uses	O
TCP	B-Protocol
(	O
typically	O
TCP	B-Protocol
ports	I-Protocol
860	O
and	O
3260	O
)	O
for	O
the	O
protocols	O
itself	O
,	O
with	O
higher-level	O
names	O
used	O
to	O
address	O
the	O
objects	O
within	O
the	O
protocol	O
.	O
</s>
<s>
Special	O
names	O
refer	O
to	O
both	O
iSCSI	B-Protocol
initiators	O
and	O
targets	O
.	O
</s>
<s>
iSCSI	B-Protocol
provides	O
three	O
name-formats	O
:	O
</s>
<s>
Format	O
:	O
The	O
iSCSI	B-Protocol
Qualified	O
Name	O
is	O
documented	O
in	O
RFC	O
3720	O
,	O
with	O
further	O
examples	O
of	O
names	O
in	O
RFC	O
3721	O
.	O
</s>
<s>
Optional	O
"	O
:	O
"	O
prefixing	O
a	O
storage	O
target	B-Application
name	O
specified	O
by	O
the	O
naming	O
authority	O
.	O
</s>
<s>
NAA	O
name	O
formats	O
were	O
added	O
to	O
iSCSI	B-Protocol
in	O
RFC	O
3980	O
,	O
to	O
provide	O
compatibility	O
with	O
naming	O
conventions	O
used	O
in	O
Fibre	B-Architecture
Channel	I-Architecture
and	O
Serial	O
Attached	O
SCSI	B-Architecture
(	O
SAS	O
)	O
storage	O
technologies	O
.	O
</s>
<s>
Usually	O
,	O
an	O
iSCSI	B-Protocol
participant	O
can	O
be	O
defined	O
by	O
three	O
or	O
four	O
fields	O
:	O
</s>
<s>
iSCSI	B-Protocol
initiators	O
can	O
locate	O
appropriate	O
storage	O
resources	O
using	O
the	O
Internet	B-Architecture
Storage	I-Architecture
Name	I-Architecture
Service	I-Architecture
(	O
iSNS	B-Architecture
)	O
protocol	O
.	O
</s>
<s>
In	O
theory	O
,	O
iSNS	B-Architecture
provides	O
iSCSI	B-Protocol
SANs	O
with	O
the	O
same	O
management	O
model	O
as	O
dedicated	O
Fibre	B-Architecture
Channel	I-Architecture
SANs	O
.	O
</s>
<s>
In	O
practice	O
,	O
administrators	O
can	O
satisfy	O
many	O
deployment	O
goals	O
for	O
iSCSI	B-Protocol
without	O
using	O
iSNS	B-Architecture
.	O
</s>
<s>
iSCSI	B-Protocol
initiators	O
and	O
targets	O
prove	O
their	O
identity	O
to	O
each	O
other	O
using	O
CHAP	B-Protocol
,	O
which	O
includes	O
a	O
mechanism	O
to	O
prevent	O
cleartext	O
passwords	O
from	O
appearing	O
on	O
the	O
wire	O
.	O
</s>
<s>
By	O
itself	O
,	O
CHAP	B-Protocol
is	O
vulnerable	O
to	O
dictionary	O
attacks	O
,	O
spoofing	O
,	O
and	O
reflection	O
attacks	O
.	O
</s>
<s>
If	O
followed	O
carefully	O
,	O
the	O
best	O
practices	O
for	O
using	O
CHAP	B-Protocol
within	O
iSCSI	B-Protocol
reduce	O
the	O
surface	O
for	O
these	O
attacks	O
and	O
mitigate	O
the	O
risks	O
.	O
</s>
<s>
Additionally	O
,	O
as	O
with	O
all	O
IP-based	O
protocols	O
,	O
IPsec	B-Protocol
can	O
operate	O
at	O
the	O
network	O
layer	O
.	O
</s>
<s>
The	O
iSCSI	B-Protocol
negotiation	O
protocol	O
is	O
designed	O
to	O
accommodate	O
other	O
authentication	O
schemes	O
,	O
though	O
interoperability	O
issues	O
limit	O
their	O
deployment	O
.	O
</s>
<s>
To	O
ensure	O
that	O
only	O
valid	O
initiators	O
connect	O
to	O
storage	B-General_Concept
arrays	I-General_Concept
,	O
administrators	O
most	O
commonly	O
run	O
iSCSI	B-Protocol
only	O
over	O
logically	O
isolated	O
backchannel	O
networks	O
.	O
</s>
<s>
In	O
this	O
deployment	O
architecture	O
,	O
only	O
the	O
management	O
ports	O
of	O
storage	B-General_Concept
arrays	I-General_Concept
are	O
exposed	O
to	O
the	O
general-purpose	O
internal	B-General_Concept
network	I-General_Concept
,	O
and	O
the	O
iSCSI	B-Protocol
protocol	O
itself	O
is	O
run	O
over	O
dedicated	O
network	O
segments	O
or	O
VLANs	B-General_Concept
.	O
</s>
<s>
This	O
mitigates	O
authentication	O
concerns	O
;	O
unauthorized	O
users	O
are	O
not	O
physically	O
provisioned	O
for	O
iSCSI	B-Protocol
,	O
and	O
thus	O
cannot	O
talk	O
to	O
storage	B-General_Concept
arrays	I-General_Concept
.	O
</s>
<s>
However	O
,	O
it	O
also	O
creates	O
a	O
transitive	O
trust	O
problem	O
,	O
in	O
that	O
a	O
single	O
compromised	O
host	O
with	O
an	O
iSCSI	B-Protocol
disk	O
can	O
be	O
used	O
to	O
attack	O
storage	O
resources	O
for	O
other	O
hosts	O
.	O
</s>
<s>
While	O
iSCSI	B-Protocol
can	O
be	O
logically	O
isolated	O
from	O
the	O
general	O
network	O
using	O
VLANs	B-General_Concept
only	O
,	O
it	O
is	O
still	O
no	O
different	O
from	O
any	O
other	O
network	O
equipment	O
and	O
may	O
use	O
any	O
cable	O
or	O
port	O
as	O
long	O
as	O
there	O
is	O
a	O
completed	O
signal	O
path	O
between	O
source	O
and	O
target	B-Application
.	O
</s>
<s>
In	O
order	O
to	O
further	O
differentiate	O
iSCSI	B-Protocol
from	O
the	O
regular	O
network	O
and	O
prevent	O
cabling	O
mistakes	O
when	O
changing	O
connections	O
,	O
administrators	O
may	O
implement	O
self-defined	O
color-coding	O
and	O
labeling	O
standards	O
,	O
such	O
as	O
only	O
using	O
yellow-colored	O
cables	O
for	O
the	O
iSCSI	B-Protocol
connections	O
and	O
only	O
blue	O
cables	O
for	O
the	O
regular	O
network	O
,	O
and	O
clearly	O
labeling	O
ports	O
and	O
switches	O
used	O
only	O
for	O
iSCSI	B-Protocol
.	O
</s>
<s>
While	O
iSCSI	B-Protocol
could	O
be	O
implemented	O
as	O
just	O
a	O
VLAN	B-General_Concept
cluster	O
of	O
ports	O
on	O
a	O
large	O
multi-port	O
switch	O
that	O
is	O
also	O
used	O
for	O
general	O
network	O
usage	O
,	O
the	O
administrator	O
may	O
instead	O
choose	O
to	O
use	O
physically	O
separate	O
switches	O
dedicated	O
to	O
iSCSI	B-Protocol
VLANs	B-General_Concept
only	O
,	O
to	O
further	O
prevent	O
the	O
possibility	O
of	O
an	O
incorrectly	O
connected	O
cable	O
plugged	O
into	O
the	O
wrong	O
port	O
bridging	O
the	O
logical	O
barrier	O
.	O
</s>
<s>
Because	O
iSCSI	B-Protocol
aims	O
to	O
consolidate	O
storage	O
for	O
many	O
servers	O
into	O
a	O
single	O
storage	B-General_Concept
array	I-General_Concept
,	O
iSCSI	B-Protocol
deployments	O
require	O
strategies	O
to	O
prevent	O
unrelated	O
initiators	O
from	O
accessing	O
storage	O
resources	O
.	O
</s>
<s>
As	O
a	O
pathological	O
example	O
,	O
a	O
single	O
enterprise	O
storage	B-General_Concept
array	I-General_Concept
could	O
hold	O
data	O
for	O
servers	O
variously	O
regulated	O
by	O
the	O
Sarbanes	O
–	O
Oxley	O
Act	O
for	O
corporate	O
accounting	O
,	O
HIPAA	O
for	O
health	O
benefits	O
information	O
,	O
and	O
PCI	B-Protocol
DSS	O
for	O
credit	O
card	O
processing	O
.	O
</s>
<s>
During	O
an	O
audit	O
,	O
storage	B-General_Concept
systems	I-General_Concept
must	O
demonstrate	O
controls	O
to	O
ensure	O
that	O
a	O
server	O
under	O
one	O
regime	O
cannot	O
access	O
the	O
storage	O
assets	O
of	O
a	O
server	O
under	O
another	O
.	O
</s>
<s>
Typically	O
,	O
iSCSI	B-Protocol
storage	B-General_Concept
arrays	I-General_Concept
explicitly	O
map	O
initiators	O
to	O
specific	O
target	B-Application
LUNs	O
;	O
an	O
initiator	O
authenticates	O
not	O
to	O
the	O
storage	B-General_Concept
array	I-General_Concept
,	O
but	O
to	O
the	O
specific	O
storage	O
asset	O
it	O
intends	O
to	O
use	O
.	O
</s>
<s>
However	O
,	O
because	O
the	O
target	B-Application
LUNs	O
for	O
SCSI	B-Architecture
commands	O
are	O
expressed	O
both	O
in	O
the	O
iSCSI	B-Protocol
negotiation	O
protocol	O
and	O
in	O
the	O
underlying	O
SCSI	B-Architecture
protocol	O
,	O
care	O
must	O
be	O
taken	O
to	O
ensure	O
that	O
access	O
control	O
is	O
provided	O
consistently	O
.	O
</s>
<s>
For	O
the	O
most	O
part	O
,	O
iSCSI	B-Protocol
operates	O
as	O
a	O
cleartext	O
protocol	O
that	O
provides	O
no	O
cryptographic	O
protection	O
for	O
data	O
in	O
motion	O
during	O
SCSI	B-Architecture
transactions	O
.	O
</s>
<s>
As	O
a	O
result	O
,	O
an	O
attacker	O
who	O
can	O
listen	O
in	O
on	O
iSCSI	B-Protocol
Ethernet	O
traffic	O
can	O
:	O
</s>
<s>
These	O
problems	O
do	O
not	O
occur	O
only	O
with	O
iSCSI	B-Protocol
,	O
but	O
rather	O
apply	O
to	O
any	O
SAN	O
protocol	O
without	O
cryptographic	O
security	O
.	O
</s>
<s>
IP-based	O
security	O
protocols	O
,	O
such	O
as	O
IPsec	B-Protocol
,	O
can	O
provide	O
standards-based	O
cryptographic	O
protection	O
to	O
this	O
traffic	O
.	O
</s>
<s>
Third-party	O
drivers	O
for	O
Windows	B-Application
and	O
Linux	B-Application
were	O
available	O
as	O
early	O
as	O
2001	O
,	O
specifically	O
for	O
attaching	O
IBM	O
's	O
IP	O
Storage	O
200i	O
appliance	O
.	O
</s>
<s>
Most	O
iSCSI	B-Protocol
targets	O
involve	O
disk	O
,	O
though	O
iSCSI	B-Protocol
tape	O
and	O
medium-changer	O
targets	O
are	O
popular	O
as	O
well	O
.	O
</s>
<s>
So	O
far	O
,	O
physical	O
devices	O
have	O
not	O
featured	O
native	O
iSCSI	B-Protocol
interfaces	O
on	O
a	O
component	O
level	O
.	O
</s>
<s>
Instead	O
,	O
devices	O
with	O
Parallel	O
SCSI	B-Architecture
or	O
Fibre	B-Architecture
Channel	I-Architecture
interfaces	O
are	O
bridged	O
by	O
using	O
iSCSI	B-Protocol
target	B-Application
software	O
,	O
external	O
bridges	O
,	O
or	O
controllers	O
internal	O
to	O
the	O
device	O
enclosure	O
.	O
</s>
<s>
The	O
underlying	O
implementation	O
can	O
deviate	O
drastically	O
from	O
the	O
presented	O
target	B-Application
as	O
is	O
done	O
with	O
virtual	B-Device
tape	I-Device
library	I-Device
(	O
VTL	O
)	O
products	O
.	O
</s>
<s>
VTLs	O
use	O
disk	O
storage	O
for	O
storing	O
data	O
written	O
to	O
virtual	B-Device
tapes	I-Device
.	O
</s>
<s>
As	O
with	O
actual	O
physical	O
devices	O
,	O
virtual	O
targets	O
are	O
presented	O
by	O
using	O
iSCSI	B-Protocol
target	B-Application
software	O
,	O
external	O
bridges	O
,	O
or	O
controllers	O
internal	O
to	O
the	O
device	O
enclosure	O
.	O
</s>
<s>
In	O
the	O
security	O
products	O
industry	O
,	O
some	O
manufacturers	O
use	O
an	O
iSCSI	B-Protocol
RAID	B-Architecture
as	O
a	O
target	B-Application
,	O
with	O
the	O
initiator	O
being	O
either	O
an	O
IP-enabled	O
encoder	O
or	O
camera	O
.	O
</s>
<s>
Multiple	O
systems	O
exist	O
that	O
allow	O
Fibre	B-Architecture
Channel	I-Architecture
,	O
SCSI	B-Architecture
and	O
SAS	O
devices	O
to	O
be	O
attached	O
to	O
an	O
IP	B-Protocol
network	I-Protocol
for	O
use	O
via	O
iSCSI	B-Protocol
.	O
</s>
<s>
They	O
can	O
be	O
used	O
to	O
allow	O
migration	O
from	O
older	O
storage	O
technologies	O
,	O
access	O
to	O
SANs	O
from	O
remote	O
servers	O
and	O
the	O
linking	O
of	O
SANs	O
over	O
IP	B-Protocol
networks	I-Protocol
.	O
</s>
<s>
An	O
iSCSI	B-Protocol
gateway	O
bridges	O
IP	O
servers	O
to	O
Fibre	B-Architecture
Channel	I-Architecture
SANs	O
.	O
</s>
<s>
The	O
TCP	B-Protocol
connection	O
is	O
terminated	O
at	O
the	O
gateway	O
,	O
which	O
is	O
implemented	O
on	O
a	O
Fibre	B-Architecture
Channel	I-Architecture
switch	O
or	O
as	O
a	O
standalone	O
appliance	O
.	O
</s>
