<s>
In	O
the	O
field	O
of	O
IPv6	B-Architecture
deployment	I-Architecture
,	O
IPv6	B-Protocol
brokenness	I-Protocol
was	O
bad	O
behavior	O
seen	O
in	O
early	O
tunneled	O
or	O
dual	O
stack	O
IPv6	B-Architecture
deployments	I-Architecture
where	O
unreliable	O
or	O
bogus	O
IPv6	B-Protocol
connectivity	O
is	O
chosen	O
in	O
preference	O
to	O
working	O
IPv4	O
connectivity	O
.	O
</s>
<s>
This	O
often	O
resulted	O
in	O
long	O
delays	O
in	O
web	O
page	O
loading	O
,	O
where	O
the	O
user	O
had	O
to	O
wait	O
for	O
each	O
attempted	O
IPv6	B-Protocol
connection	O
to	O
time	O
out	O
before	O
the	O
IPv4	O
connection	O
was	O
tried	O
.	O
</s>
<s>
IPv6	B-Protocol
brokenness	I-Protocol
is	O
now	O
generally	O
regarded	O
as	O
a	O
solved	O
problem	O
for	O
almost	O
all	O
practical	O
purposes	O
,	O
following	O
improvements	O
at	O
both	O
the	O
transport	O
and	O
application	O
layers	O
.	O
</s>
<s>
As	O
of	O
May	O
2011	O
,	O
IPv6	B-Protocol
brokenness	I-Protocol
as	O
measured	O
by	O
instrumenting	O
a	O
set	O
of	O
mainstream	O
Norwegian	O
websites	O
was	O
down	O
to	O
~	O
0.015	O
%	O
,	O
most	O
of	O
which	O
was	O
caused	O
by	O
older	O
versions	O
of	O
Mac	B-Operating_System
OS	I-Operating_System
X	I-Operating_System
which	O
would	O
often	O
prefer	O
non-working	O
IPv6	B-Protocol
connectivity	O
when	O
it	O
was	O
not	O
justified	O
.	O
</s>
<s>
However	O
,	O
there	O
was	O
no	O
upgrade	O
path	O
for	O
PowerPC-based	O
Macs	O
.	O
</s>
<s>
The	O
main	O
remaining	O
problem	O
for	O
Mac	B-Operating_System
OS	I-Operating_System
X	I-Operating_System
was	O
the	O
presence	O
of	O
rogue	O
routers	O
,	O
such	O
as	O
wrongly	O
configured	O
Windows	O
Internet	B-Protocol
Connection	I-Protocol
Sharing	I-Protocol
devices	O
pretending	O
to	O
have	O
IPv6	B-Protocol
connectivity	O
,	O
while	O
6to4	O
tunneled	O
IPv6	B-Protocol
traffic	O
is	O
blocked	O
at	O
a	O
firewall	O
.	O
</s>
<s>
Following	O
World	O
IPv6	B-Protocol
Day	O
in	O
July	O
2011	O
,	O
there	O
were	O
reports	O
of	O
a	O
substantial	O
reduction	O
in	O
IPv6	B-Protocol
brokenness	I-Protocol
as	O
a	O
result	O
of	O
that	O
experiment	O
.	O
</s>
<s>
In	O
the	O
year	O
following	O
the	O
trial	O
,	O
but	O
prior	O
to	O
the	O
World	O
IPv6	B-Protocol
Launch	O
date	O
,	O
brokenness	O
levels	O
were	O
reported	O
to	O
have	O
risen	O
slowly	O
back	O
upwards	O
again	O
towards	O
0.03	O
%	O
.	O
</s>
<s>
Google	B-Application
,	O
a	O
major	O
provider	O
of	O
services	O
on	O
the	O
Internet	O
,	O
experimented	O
with	O
using	O
a	O
type	O
of	O
DNS	B-Protocol
whitelisting	I-Protocol
on	O
a	O
per-ISP	O
basis	O
to	O
prevent	O
this	O
until	O
the	O
World	O
IPv6	B-Protocol
Launch	O
.	O
</s>
<s>
In	O
the	O
DNS	B-Protocol
whitelisting	I-Protocol
approach	O
,	O
ISPs	O
are	O
determined	O
from	O
DNS	B-Protocol
lookup	I-Protocol
source	O
IP	O
addresses	O
by	O
correlating	O
them	O
with	O
network	O
prefixes	O
derived	O
from	O
routing	B-Protocol
tables	I-Protocol
.	O
</s>
<s>
There	O
is	O
an	O
entitled	O
"	O
IPv6	B-Protocol
AAAA	O
DNS	B-Protocol
Whitelisting	I-Protocol
Implications	O
"	O
that	O
describes	O
the	O
issues	O
around	O
whitelisting	O
.	O
</s>
<s>
AAAA	O
records	O
are	O
only	O
sent	O
to	O
ISPs	O
that	O
can	O
demonstrate	O
that	O
they	O
are	O
providing	O
reliable	O
IPv6	B-Protocol
to	O
their	O
customers	O
.	O
</s>
<s>
Other	O
ISPs	O
are	O
sent	O
only	O
A	O
records	O
,	O
thus	O
preventing	O
users	O
from	O
attempting	O
to	O
connect	O
over	O
IPv6	B-Protocol
when	O
hostnames	O
are	O
used	O
instead	O
of	O
ipv6-addresses	O
.	O
</s>
<s>
Numerous	O
concerns	O
were	O
raised	O
about	O
the	O
practicality	O
of	O
DNS	B-Protocol
whitelisting	I-Protocol
as	O
a	O
long-term	O
large-scale	O
solution	O
,	O
such	O
as	O
scalability	O
and	O
maintenance	O
issues	O
relating	O
to	O
the	O
maintenance	O
of	O
large	O
numbers	O
of	O
bilateral	O
agreements	O
.	O
</s>
<s>
In	O
2010	O
,	O
several	O
of	O
the	O
major	O
web	O
service	O
providers	O
met	O
to	O
discuss	O
pooling	O
their	O
DNS	B-Protocol
whitelisting	I-Protocol
information	O
in	O
an	O
attempt	O
to	O
avoid	O
these	O
scaling	O
problems	O
.	O
</s>
<s>
It	O
appears	O
that	O
no	O
major	O
content	O
providers	O
eventually	O
ended	O
up	O
using	O
the	O
whitelisting	O
approach	O
,	O
given	O
that	O
all	O
that	O
had	O
previously	O
declared	O
an	O
interest	O
began	O
serving	O
AAAA	O
records	O
to	O
generic	O
DNS	O
queries	O
following	O
World	O
IPv6	B-Protocol
Launch	O
Day	O
.	O
</s>
<s>
Google	B-Application
now	O
provides	O
AAAA	O
records	O
to	O
all	O
DNS	O
servers	O
except	O
for	O
those	O
on	O
a	O
limited	O
list	O
of	O
subnets	O
which	O
Google	B-Application
excludes	O
from	O
AAAA	O
record	O
service	O
.	O
</s>
<s>
As	O
of	O
2017	O
,	O
IPv6	B-Protocol
brokenness	I-Protocol
is	O
now	O
generally	O
regarded	O
as	O
a	O
non-problem	O
.	O
</s>
<s>
This	O
is	O
due	O
to	O
two	O
factors	O
:	O
firstly	O
,	O
IPv6	B-Protocol
transport	O
is	O
much	O
improved	O
,	O
so	O
that	O
the	O
underlying	O
error	O
rate	O
is	O
much	O
reduced	O
,	O
and	O
secondly	O
,	O
that	O
common	O
applications	O
such	O
as	O
web	O
browsers	O
now	O
use	O
fast	B-Protocol
fallback	I-Protocol
methods	O
such	O
as	O
the	O
"	O
Happy	B-Protocol
Eyeballs	I-Protocol
"	O
algorithm	O
to	O
select	O
whichever	O
protocol	O
works	O
best	O
.	O
</s>
<s>
Some	O
operating	O
system	O
vendors	O
have	O
rolled	O
fast	B-Protocol
fallback	I-Protocol
algorithms	O
into	O
their	O
higher-level	O
network	B-Protocol
stack	I-Protocol
APIs	O
,	O
thus	O
making	O
the	O
solution	O
available	O
for	O
all	O
programs	O
that	O
use	O
those	O
APIs	O
to	O
make	O
connections	O
.	O
</s>
