<s>
A	O
root	B-Application
name	I-Application
server	I-Application
is	O
a	O
name	B-Protocol
server	I-Protocol
for	O
the	O
root	B-Protocol
zone	I-Protocol
of	O
the	O
Domain	B-Protocol
Name	I-Protocol
System	I-Protocol
(	O
DNS	B-Protocol
)	O
of	O
the	O
Internet	O
.	O
</s>
<s>
It	O
directly	O
answers	O
requests	O
for	O
records	O
in	O
the	O
root	B-Protocol
zone	I-Protocol
and	O
answers	O
other	O
requests	O
by	O
returning	O
a	O
list	O
of	O
the	O
authoritative	O
name	B-Protocol
servers	I-Protocol
for	O
the	O
appropriate	O
top-level	O
domain	O
(	O
TLD	O
)	O
.	O
</s>
<s>
The	O
root	B-Application
name	I-Application
servers	I-Application
are	O
a	O
critical	O
part	O
of	O
the	O
Internet	O
infrastructure	O
because	O
they	O
are	O
the	O
first	O
step	O
in	O
resolving	O
human-readable	O
host	O
names	O
into	O
IP	B-Protocol
addresses	I-Protocol
that	O
are	O
used	O
in	O
communication	O
between	O
Internet	B-Device
hosts	I-Device
.	O
</s>
<s>
A	O
combination	O
of	O
limits	O
in	O
the	O
DNS	B-Protocol
and	O
certain	O
protocols	O
,	O
namely	O
the	O
practical	O
size	O
of	O
unfragmented	O
User	B-Protocol
Datagram	I-Protocol
Protocol	I-Protocol
(	O
UDP	O
)	O
packets	O
,	O
resulted	O
in	O
a	O
decision	O
to	O
limit	O
the	O
number	O
of	O
root	B-Application
servers	I-Application
to	O
thirteen	O
server	O
addresses	O
.	O
</s>
<s>
The	O
use	O
of	O
anycast	B-Protocol
addressing	O
permits	O
the	O
actual	O
number	O
of	O
root	B-Application
server	I-Application
instances	O
to	O
be	O
much	O
larger	O
,	O
and	O
is	O
1,553	O
.	O
</s>
<s>
The	O
DNS	B-Protocol
is	O
a	O
hierarchical	O
naming	O
system	O
for	O
computers	O
,	O
services	O
,	O
or	O
any	O
resource	O
participating	O
in	O
the	O
Internet	O
.	O
</s>
<s>
The	O
top	O
of	O
that	O
hierarchy	O
is	O
the	O
root	B-Protocol
domain	I-Protocol
.	O
</s>
<s>
The	O
root	B-Protocol
domain	I-Protocol
does	O
not	O
have	O
a	O
formal	O
name	O
and	O
its	O
label	O
in	O
the	O
DNS	B-Protocol
hierarchy	O
is	O
an	O
empty	O
string	O
.	O
</s>
<s>
All	O
fully	B-Protocol
qualified	I-Protocol
domain	I-Protocol
names	I-Protocol
(	O
FQDNs	B-Protocol
)	O
on	O
the	O
Internet	O
can	O
be	O
regarded	O
as	O
ending	O
with	O
this	O
empty	O
string	O
for	O
the	O
root	B-Protocol
domain	I-Protocol
,	O
and	O
therefore	O
ending	O
in	O
a	O
full	O
stop	O
character	O
(	O
the	O
label	O
delimiter	O
)	O
,	O
e.g.	O
,	O
""	O
.	O
</s>
<s>
This	O
is	O
generally	O
implied	O
rather	O
than	O
explicit	O
,	O
as	O
modern	O
DNS	B-Protocol
software	O
does	O
not	O
actually	O
require	O
that	O
the	O
terminating	O
dot	O
be	O
included	O
when	O
attempting	O
to	O
translate	O
a	O
domain	O
name	O
to	O
an	O
IP	B-Protocol
address	I-Protocol
.	O
</s>
<s>
The	O
root	B-Protocol
domain	I-Protocol
contains	O
all	O
top-level	O
domains	O
of	O
the	O
Internet	O
.	O
</s>
<s>
,	O
it	O
contained	O
1058	O
TLDs	O
,	O
including	O
730	O
generic	O
top-level	O
domains	O
(	O
gTLDs	O
)	O
and	O
301	O
country	B-Application
code	I-Application
top-level	I-Application
domains	I-Application
(	O
ccTLDs	B-Application
)	O
in	O
the	O
root	B-Protocol
domain	I-Protocol
.	O
</s>
<s>
A	O
domain	O
is	O
used	O
for	O
testing	O
internationalized	B-Language
domain	I-Language
names	I-Language
.	O
</s>
<s>
The	O
first	O
component	O
(	O
TLD	O
)	O
is	O
queried	O
using	O
a	O
root	B-Application
server	I-Application
to	O
obtain	O
the	O
responsible	O
authoritative	O
server	O
.	O
</s>
<s>
Queries	O
for	O
each	O
label	O
return	O
more	O
specific	O
name	B-Protocol
servers	I-Protocol
until	O
a	O
name	B-Protocol
server	I-Protocol
returns	O
the	O
answer	O
of	O
the	O
original	O
query	O
.	O
</s>
<s>
In	O
practice	O
,	O
most	O
of	O
this	O
information	O
does	O
not	O
change	O
very	O
often	O
over	O
a	O
period	O
of	O
hours	O
and	O
therefore	O
it	O
is	O
cached	B-General_Concept
by	O
intermediate	O
name	B-Protocol
servers	I-Protocol
or	O
by	O
a	O
name	O
cache	B-General_Concept
built	O
into	O
the	O
user	O
's	O
application	O
.	O
</s>
<s>
DNS	B-Protocol
lookups	O
to	O
the	O
root	B-Application
name	I-Application
servers	I-Application
may	O
therefore	O
be	O
relatively	O
infrequent	O
.	O
</s>
<s>
A	O
survey	O
in	O
2003	O
reported	O
that	O
only	O
2%	O
of	O
all	O
queries	O
to	O
the	O
root	B-Application
servers	I-Application
were	O
legitimate	O
.	O
</s>
<s>
Incorrect	O
or	O
non-existent	O
caching	B-General_Concept
was	O
responsible	O
for	O
75%	O
of	O
the	O
queries	O
,	O
12.5	O
%	O
were	O
for	O
unknown	O
TLDs	O
,	O
7%	O
were	O
for	O
lookups	O
using	O
IP	B-Protocol
addresses	I-Protocol
as	O
if	O
they	O
were	O
domain	O
names	O
,	O
etc	O
.	O
</s>
<s>
Some	O
misconfigured	O
desktop	O
computers	O
even	O
tried	O
to	O
update	O
the	O
root	B-Application
server	I-Application
records	O
for	O
the	O
TLDs	O
.	O
</s>
<s>
Although	O
any	O
local	O
implementation	O
of	O
DNS	B-Protocol
can	O
implement	O
its	O
own	O
private	O
root	B-Application
name	I-Application
servers	I-Application
,	O
the	O
term	O
"	O
root	B-Application
name	I-Application
server	I-Application
"	O
is	O
generally	O
used	O
to	O
describe	O
the	O
thirteen	O
well-known	O
root	B-Application
name	I-Application
servers	I-Application
that	O
implement	O
the	O
root	O
name	O
space	O
domain	O
for	O
the	O
Internet	O
's	O
official	O
global	O
implementation	O
of	O
the	O
Domain	B-Protocol
Name	I-Protocol
System	I-Protocol
.	O
</s>
<s>
Resolvers	O
use	O
a	O
small	O
3	O
KB	O
root.hints	O
file	O
published	O
by	O
Internic	O
to	O
bootstrap	O
this	O
initial	O
list	O
of	O
root	B-Application
server	I-Application
addresses	O
.	O
</s>
<s>
There	O
are	O
13	O
logical	O
root	B-Application
name	I-Application
servers	I-Application
specified	O
,	O
with	O
logical	O
names	O
in	O
the	O
form	O
,	O
where	O
ranges	O
from	O
a	O
to	O
m	O
.	O
The	O
choice	O
of	O
thirteen	O
name	B-Protocol
servers	I-Protocol
was	O
made	O
because	O
of	O
limitations	O
in	O
the	O
original	O
DNS	B-Protocol
specification	O
,	O
which	O
specifies	O
a	O
maximum	O
packet	O
size	O
of	O
512	O
bytes	O
when	O
using	O
the	O
User	B-Protocol
Datagram	I-Protocol
Protocol	I-Protocol
(	O
UDP	O
)	O
.	O
</s>
<s>
Technically	O
however	O
,	O
fourteen	O
name	B-Protocol
servers	I-Protocol
fit	O
into	O
an	O
IPv4	B-Protocol
packet	O
.	O
</s>
<s>
The	O
addition	O
of	O
IPv6	B-Protocol
addresses	O
for	O
the	O
root	B-Application
name	I-Application
servers	I-Application
requires	O
more	O
than	O
512	O
bytes	O
,	O
which	O
is	O
facilitated	O
by	O
the	O
EDNS0	B-Protocol
extension	I-Protocol
to	O
the	O
DNS	B-Protocol
standard	O
.	O
</s>
<s>
Additionally	O
,	O
all	O
operate	O
in	O
multiple	O
geographical	O
locations	O
using	O
a	O
routing	O
technique	O
called	O
anycast	B-Protocol
addressing	O
,	O
providing	O
increased	O
performance	O
and	O
even	O
more	O
fault	O
tolerance	O
.	O
</s>
<s>
An	O
informational	O
homepage	O
exists	O
for	O
every	O
logical	O
server	O
(	O
except	O
G-Root	B-Application
)	O
under	O
the	O
domain	O
with	O
web	O
address	O
in	O
the	O
form	O
,	O
where	O
ranges	O
from	O
a	O
to	O
m	O
.	O
</s>
<s>
Ten	O
servers	O
were	O
originally	O
in	O
the	O
United	O
States	O
;	O
all	O
are	O
now	O
operated	O
using	O
anycast	B-Protocol
addressing	O
.	O
</s>
<s>
Three	O
servers	O
were	O
originally	O
located	O
in	O
Stockholm	O
(	O
I-Root	B-Application
)	O
,	O
Amsterdam	O
(	O
K-Root	B-Application
)	O
,	O
and	O
Tokyo	O
(	O
M-Root	B-Application
)	O
respectively	O
.	O
</s>
<s>
With	O
anycast	B-Protocol
,	O
most	O
of	O
the	O
physical	O
root	B-Application
servers	I-Application
are	O
now	O
outside	O
the	O
United	O
States	O
,	O
allowing	O
for	O
high	O
performance	O
worldwide	O
.	O
</s>
<s>
Letter	O
IPv4	B-Protocol
address	O
IPv6	B-Protocol
address	O
AS-numberAS-numbers	O
and	O
IP-addresses	O
from	O
Root-servers.org	O
homepage	O
checked	O
9	O
January	O
2014	O
Old	O
name	O
Operator	O
Location	O
&	O
no	O
.	O
</s>
<s>
ofsites	O
(	O
global/local	O
)	O
Location	O
and	O
sites	O
from	O
Root-servers.org	O
homepage	O
checked	O
10	O
October	O
2014	O
Software	O
A	O
AS19836	O
,	O
AS19836	O
is	O
not	O
listed	O
by	O
the	O
RIPEstat	O
tool	O
,	O
though	O
one	O
can	O
see	O
it	O
in	O
https://stat.ripe.net/AS19836#tabId=at-a-glance	O
AS36619	O
,	O
AS36620	O
,	O
AS36622	O
,	O
AS36625	O
,	O
AS36631	O
,	O
AS64820AS64820	O
is	O
listed	O
as	O
"	O
private	O
use	O
"	O
in	O
RIPE	O
's	O
RISwhois	O
tool	O
ns.internic.net	O
Verisign	B-Application
Distributed	O
using	O
anycast14/2NSD	O
and	O
Verisign	B-Application
ATLAS	O
B	O
Originally	O
it	O
was	O
;	O
It	O
was	O
changed	O
to	O
from	O
January	O
2004	O
to	O
October	O
2017	O
.	O
</s>
<s>
AS394353	O
ns1.isi.edu	O
USC-ISI	O
Distributed	O
using	O
anycast6/0	O
BIND	B-Protocol
and	O
Knot	B-Protocol
DNS	I-Protocol
C	O
AS2149	O
c.psi.net	O
Cogent	O
Communications	O
Distributed	O
using	O
anycast10/0	O
BIND	B-Protocol
D	O
Since	O
3	O
January	O
2013	O
;	O
originally	O
was	O
.	O
</s>
<s>
AS10886Since	O
November	O
2017	O
;	O
originally	O
was	O
AS27.RISwhois	O
,	O
excluding	O
less-specific	O
AS3303	O
route	O
announcement	O
terp.umd.edu	O
University	O
of	O
Maryland	O
Distributed	O
using	O
anycast22/127	O
NSDD-root	O
History	O
page	O
E	O
AS21556	O
ns.nasa.gov	O
NASA	O
Ames	O
Research	O
Center	O
Distributed	O
using	O
anycast117/137	O
BIND	B-Protocol
and	O
NSD	B-Protocol
F	O
AS3557	O
ns.isc.org	O
Internet	O
Systems	O
Consortium	O
Distributed	O
using	O
anycast119/119	O
BIND	B-Protocol
GFormerly	O
http://www.nic.mil/	O
(	O
Internet	O
Archive	O
link	O
)	O
;	O
unlike	O
all	O
other	O
DNS	B-Application
root	I-Application
servers	I-Application
,	O
G-Root	B-Application
does	O
not	O
implement	O
a	O
homepage	O
under	O
root-servers.org,	O
i.e.	O
</s>
<s>
http://g.root-servers.org/	O
.	O
</s>
<s>
Unlike	O
all	O
other	O
DNS	B-Application
root	I-Application
servers	I-Application
,	O
G-Root	B-Application
does	O
not	O
respond	O
to	O
pings	B-Protocol
.	O
</s>
<s>
AS5927	O
ns.nic.ddn.mil	O
Defense	O
Information	O
Systems	O
Agency	O
Distributed	O
using	O
anycast6/0	O
BIND	B-Protocol
H	O
Since	O
1	O
December	O
2015	O
;	O
originally	O
was	O
.	O
</s>
<s>
aos.arl.army.mil	O
U.S.	O
Army	O
Research	O
Lab	O
Distributed	O
using	O
anycast8/0	O
NSD	B-Protocol
I	O
AS29216	O
nic.nordu.net	O
Netnod	O
Distributed	O
using	O
anycast63/2	O
BIND	B-Protocol
J	O
Since	O
November	O
2002	O
;	O
originally	O
was	O
.	O
</s>
<s>
AS26415	O
,	O
AS36626	O
,	O
AS36628	O
,	O
AS36632	O
Verisign	B-Application
Distributed	O
using	O
anycast63/55NSD	O
and	O
Verisign	B-Application
ATLAS	O
K	O
AS25152	O
RIPE	O
NCC	O
Distributed	O
using	O
anycast70/3	O
BIND	B-Protocol
,	O
NSD	B-Protocol
and	O
Knot	O
DNSK-root	O
Homepage	O
L	O
Since	O
1	O
November	O
2007	O
;	O
originally	O
was	O
.	O
</s>
<s>
There	O
are	O
also	O
several	O
alternative	O
namespace	O
systems	O
with	O
an	O
alternative	B-Protocol
DNS	I-Protocol
root	I-Protocol
using	O
their	O
own	O
set	O
of	O
root	B-Application
name	I-Application
servers	I-Application
that	O
exist	O
in	O
parallel	O
to	O
the	O
mainstream	O
name	B-Protocol
servers	I-Protocol
.	O
</s>
<s>
The	O
first	O
,	O
AlterNIC	B-Protocol
,	O
generated	O
a	O
substantial	O
amount	O
of	O
press	O
.	O
</s>
<s>
The	O
function	O
of	O
a	O
root	B-Application
name	I-Application
server	I-Application
may	O
also	O
be	O
implemented	O
locally	O
,	O
or	O
on	O
a	O
provider	O
network	O
.	O
</s>
<s>
Such	O
servers	O
are	O
synchronized	O
with	O
the	O
official	O
root	B-Protocol
zone	I-Protocol
file	O
by	O
ICANN	B-Application
,	O
and	O
do	O
not	O
constitute	O
an	O
alternate	O
root	O
.	O
</s>
<s>
As	O
the	O
root	B-Application
name	I-Application
servers	I-Application
are	O
an	O
important	O
part	O
of	O
the	O
Internet	O
,	O
they	O
have	O
come	O
under	O
attack	O
several	O
times	O
,	O
although	O
none	O
of	O
the	O
attacks	O
have	O
ever	O
been	O
serious	O
enough	O
to	O
severely	O
affect	O
the	O
performance	O
of	O
the	O
Internet	O
.	O
</s>
<s>
The	O
DNS	B-Application
Root	I-Application
Server	I-Application
System	I-Application
Advisory	I-Application
Committee	I-Application
is	O
an	O
ICANN	B-Application
committee	O
.	O
</s>
<s>
ICANN	B-Application
's	O
bylaws	O
assign	O
authority	O
over	O
the	O
operation	O
of	O
the	O
root	B-Application
name	I-Application
servers	I-Application
of	O
the	O
Domain	B-Protocol
Name	I-Protocol
System	I-Protocol
to	O
the	O
DNS	B-Application
Root	I-Application
Server	I-Application
System	I-Application
Advisory	I-Application
Committee	I-Application
.	O
</s>
<s>
The	O
root	B-Protocol
zone	I-Protocol
file	O
is	O
a	O
small	O
(	O
about	O
2	O
MB	O
)	O
data	O
set	O
whose	O
publication	O
is	O
the	O
primary	O
purpose	O
of	O
root	B-Application
name	I-Application
servers	I-Application
.	O
</s>
<s>
The	O
root	B-Protocol
zone	I-Protocol
file	O
is	O
at	O
the	O
apex	O
of	O
a	O
hierarchical	O
distributed	O
database	O
called	O
the	O
Domain	B-Protocol
Name	I-Protocol
System	I-Protocol
(	O
DNS	B-Protocol
)	O
.	O
</s>
<s>
This	O
database	O
is	O
used	O
by	O
almost	O
all	O
Internet	O
applications	O
to	O
translate	O
worldwide	O
unique	O
names	O
such	O
as	O
www.wikipedia.org	O
into	O
other	O
identifiers	O
such	O
as	O
IP	B-Protocol
addresses	I-Protocol
.	O
</s>
<s>
The	O
contents	O
of	O
the	O
root	B-Protocol
zone	I-Protocol
file	O
is	O
a	O
list	O
of	O
names	O
and	O
numeric	O
IP	B-Protocol
addresses	I-Protocol
of	O
the	O
root	B-Protocol
domain	I-Protocol
authoritative	B-Protocol
DNS	I-Protocol
servers	I-Protocol
for	O
all	O
top-level	O
domains	O
(	O
TLDs	O
)	O
such	O
as	O
com	O
,	O
org	O
,	O
edu	O
,	O
and	O
the	O
country	B-Application
code	I-Application
top-level	I-Application
domains	I-Application
(	O
it	O
also	O
includes	O
that	O
info	O
for	O
root	B-Protocol
domain	I-Protocol
,	O
the	O
dot	O
)	O
.	O
</s>
<s>
,	O
the	O
root	B-Protocol
zone	I-Protocol
consisted	O
of	O
1511	O
useful	O
TLDs	O
(	O
excluded	O
are	O
:	O
55	O
domains	O
that	O
are	O
not	O
assigned	O
,	O
8	O
that	O
are	O
retired	O
,	O
and	O
11	O
test	O
domains	O
)	O
.	O
</s>
<s>
Other	O
name	B-Protocol
servers	I-Protocol
forward	O
queries	O
for	O
which	O
they	O
do	O
not	O
have	O
any	O
information	O
about	O
authoritative	O
servers	O
to	O
a	O
root	B-Application
name	I-Application
server	I-Application
.	O
</s>
<s>
The	O
root	B-Application
name	I-Application
server	I-Application
,	O
using	O
its	O
root	B-Protocol
zone	I-Protocol
file	O
,	O
answers	O
with	O
a	O
referral	O
to	O
the	O
authoritative	O
servers	O
for	O
the	O
appropriate	O
TLD	O
or	O
with	O
an	O
indication	O
that	O
no	O
such	O
TLD	O
exists	O
.	O
</s>
