<s>
In	O
computer	B-Architecture
networking	I-Architecture
,	O
peering	B-Protocol
is	O
a	O
voluntary	O
interconnection	O
of	O
administratively	O
separate	O
Internet	O
networks	B-Architecture
for	O
the	O
purpose	O
of	O
exchanging	O
traffic	O
between	O
the	O
"	O
down-stream	O
"	O
users	O
of	O
each	O
network	O
.	O
</s>
<s>
Peering	B-Protocol
is	O
settlement-free	O
,	O
also	O
known	O
as	O
"	O
bill-and-keep	O
,	O
"	O
or	O
"	O
sender	O
keeps	O
all	O
,	O
"	O
meaning	O
that	O
neither	O
party	O
pays	O
the	O
other	O
in	O
association	O
with	O
the	O
exchange	O
of	O
traffic	O
;	O
instead	O
,	O
each	O
derives	O
and	O
retains	O
revenue	O
from	O
its	O
own	O
customers	O
.	O
</s>
<s>
An	O
agreement	O
by	O
two	O
or	O
more	O
networks	B-Architecture
to	O
peer	O
is	O
instantiated	O
by	O
a	O
physical	O
interconnection	O
of	O
the	O
networks	B-Architecture
,	O
an	O
exchange	O
of	O
routing	B-Protocol
information	I-Protocol
through	O
the	O
Border	B-Protocol
Gateway	I-Protocol
Protocol	I-Protocol
(	O
BGP	B-Protocol
)	O
routing	B-Protocol
protocol	O
,	O
tacit	O
agreement	O
to	O
norms	O
of	O
conduct	O
and	O
,	O
in	O
some	O
extraordinarily	O
rare	O
cases	O
(	O
0.07	O
%	O
)	O
,	O
a	O
formalized	O
contractual	O
document	O
.	O
</s>
<s>
In	O
0.02	O
%	O
of	O
cases	O
the	O
word	O
"	O
peering	B-Protocol
"	O
is	O
used	O
to	O
describe	O
situations	O
where	O
there	O
is	O
some	O
settlement	O
involved	O
.	O
</s>
<s>
Because	O
these	O
outliers	O
can	O
be	O
viewed	O
as	O
creating	O
ambiguity	O
,	O
the	O
phrase	O
"	O
settlement-free	B-Protocol
peering	I-Protocol
"	O
is	O
sometimes	O
used	O
to	O
explicitly	O
denote	O
normal	O
cost-free	O
peering	B-Protocol
.	O
</s>
<s>
The	O
first	O
Internet	B-Protocol
exchange	I-Protocol
point	I-Protocol
was	O
the	O
Commercial	O
Internet	B-Protocol
eXchange	I-Protocol
(	O
CIX	O
)	O
,	O
formed	O
by	O
Alternet/UUNET	O
(	O
now	O
Verizon	B-Application
Business	I-Application
)	O
,	O
PSI	O
,	O
and	O
CERFNET	O
to	O
exchange	O
traffic	O
without	O
regard	O
for	O
whether	O
the	O
traffic	O
complied	O
with	O
the	O
acceptable	B-Application
use	I-Application
policy	I-Application
(	O
AUP	O
)	O
of	O
the	O
NSFNet	O
or	O
ANS	O
 '	O
interconnection	O
policy	O
.	O
</s>
<s>
The	O
router	O
was	O
later	O
moved	O
to	O
the	O
Palo	O
Alto	O
Internet	B-Protocol
Exchange	I-Protocol
,	O
or	O
PAIX	O
,	O
which	O
was	O
developed	O
and	O
operated	O
by	O
Digital	O
Equipment	O
Corporation	O
(	O
DEC	O
)	O
.	O
</s>
<s>
Because	O
the	O
CIX	O
operated	O
at	O
OSI	O
layer	O
3	O
,	O
rather	O
than	O
OSI	B-Protocol
layer	I-Protocol
2	I-Protocol
,	O
and	O
because	O
it	O
was	O
not	O
neutral	O
,	O
in	O
the	O
sense	O
that	O
it	O
was	O
operated	O
by	O
one	O
of	O
its	O
participants	O
rather	O
than	O
by	O
all	O
of	O
them	O
collectively	O
,	O
and	O
it	O
conducted	O
lobbying	O
activities	O
supported	O
by	O
some	O
of	O
its	O
participants	O
and	O
not	O
by	O
others	O
,	O
it	O
would	O
not	O
today	O
be	O
considered	O
an	O
Internet	B-Protocol
exchange	I-Protocol
point	I-Protocol
.	O
</s>
<s>
The	O
first	O
exchange	O
point	O
to	O
resemble	O
modern	O
,	O
neutral	O
,	O
Ethernet-based	O
exchanges	O
was	O
the	O
Metropolitan	O
Area	O
Ethernet	O
,	O
or	O
MAE	O
,	O
in	O
Tysons	O
Corner	O
,	O
Virginia	B-Application
.	O
</s>
<s>
When	O
the	O
United	O
States	O
government	O
de-funded	O
the	O
NSFNET	O
backbone	O
,	O
Internet	B-Protocol
exchange	I-Protocol
points	I-Protocol
were	O
needed	O
to	O
replace	O
its	O
function	O
,	O
and	O
initial	O
governmental	O
funding	O
was	O
used	O
to	O
aid	O
the	O
preexisting	O
MAE	O
and	O
bootstrap	O
three	O
other	O
exchanges	O
,	O
which	O
they	O
dubbed	O
NAPs	O
,	O
or	O
"	O
Network	O
Access	O
Points	O
,	O
"	O
in	O
accordance	O
with	O
the	O
terminology	O
of	O
the	O
National	O
Information	O
Infrastructure	O
document	O
.	O
</s>
<s>
All	O
four	O
are	O
now	O
defunct	O
or	O
no	O
longer	O
functioning	O
as	O
Internet	B-Protocol
exchange	I-Protocol
points	I-Protocol
:	O
</s>
<s>
As	O
the	O
Internet	O
grew	O
,	O
and	O
traffic	O
levels	O
increased	O
,	O
these	O
NAPs	O
became	O
a	O
network	B-Protocol
bottleneck	I-Protocol
.	O
</s>
<s>
Most	O
of	O
the	O
early	O
NAPs	O
utilized	O
FDDI	B-Protocol
technology	O
,	O
which	O
provided	O
only	O
100	O
Mbit/s	O
of	O
capacity	O
to	O
each	O
participant	O
.	O
</s>
<s>
Other	O
prospective	O
exchange	O
point	O
operators	O
moved	O
directly	O
into	O
offering	O
Ethernet	O
technology	O
,	O
such	O
as	O
gigabit	O
Ethernet	O
(	O
1,000	O
Mbit/s	O
)	O
,	O
which	O
quickly	O
became	O
the	O
predominant	O
choice	O
for	O
Internet	B-Protocol
exchange	I-Protocol
points	I-Protocol
due	O
to	O
the	O
reduced	O
cost	O
and	O
increased	O
capacity	O
offered	O
.	O
</s>
<s>
Today	O
,	O
almost	O
all	O
significant	O
exchange	B-Protocol
points	I-Protocol
operate	O
solely	O
over	O
Ethernet	O
,	O
and	O
most	O
of	O
the	O
largest	O
exchange	B-Protocol
points	I-Protocol
offer	O
10	O
,	O
40	O
,	O
and	O
even	O
100	B-Protocol
gigabit	I-Protocol
service	O
.	O
</s>
<s>
During	O
the	O
dot-com	O
boom	O
,	O
many	O
exchange	O
point	O
and	O
carrier-neutral	O
colocation	B-Application
providers	O
had	O
plans	O
to	O
build	O
as	O
many	O
as	O
50	O
locations	O
to	O
promote	O
carrier	O
interconnection	O
in	O
the	O
United	O
States	O
alone	O
.	O
</s>
<s>
Essentially	O
all	O
of	O
these	O
plans	O
were	O
abandoned	O
following	O
the	O
dot-com	O
bust	O
,	O
and	O
today	O
it	O
is	O
considered	O
both	O
economically	O
and	O
technically	O
infeasible	O
to	O
support	O
this	O
level	O
of	O
interconnection	O
among	O
even	O
the	O
largest	O
of	O
networks	B-Architecture
.	O
</s>
<s>
The	O
Internet	O
is	O
a	O
collection	O
of	O
separate	O
and	O
distinct	O
networks	B-Architecture
referred	O
to	O
as	O
autonomous	B-Architecture
systems	I-Architecture
,	O
each	O
one	O
consisting	O
of	O
a	O
set	O
of	O
globally	O
unique	O
IP	B-Protocol
addresses	I-Protocol
and	O
a	O
unique	O
global	O
BGP	B-Protocol
routing	B-Protocol
policy	O
.	O
</s>
<s>
The	O
interconnection	O
relationships	O
between	O
Autonomous	B-Architecture
Systems	I-Architecture
are	O
of	O
exactly	O
two	O
types	O
:	O
</s>
<s>
Peering	B-Protocol
-	O
Two	O
networks	B-Architecture
exchange	O
traffic	O
between	O
their	O
users	O
freely	O
,	O
and	O
for	O
mutual	O
benefit	O
.	O
</s>
<s>
Transit	B-Application
–	O
One	O
network	O
pays	O
another	O
network	O
for	O
access	O
to	O
the	O
Internet	O
.	O
</s>
<s>
Sell	O
transit	B-Application
service	O
to	O
that	O
network	O
or	O
a	O
chain	O
of	O
resellers	O
ending	O
at	O
that	O
network	O
(	O
making	O
them	O
a	O
'	O
customer	O
 '	O
)	O
,	O
</s>
<s>
Buy	O
transit	B-Application
service	O
from	O
any	O
other	O
network	O
(	O
which	O
is	O
then	O
responsible	O
for	O
providing	O
interconnection	O
to	O
the	O
rest	O
of	O
the	O
Internet	O
)	O
.	O
</s>
<s>
Therefore	O
,	O
a	O
network	O
is	O
connected	O
to	O
the	O
Internet	O
if	O
and	O
only	O
if	O
it	O
buys	O
transit	B-Application
,	O
or	O
peers	O
with	O
every	O
other	O
network	O
which	O
also	O
does	O
not	O
purchase	O
transit	B-Application
(	O
which	O
together	O
constitute	O
a	O
"	O
default	B-Protocol
free	I-Protocol
zone	I-Protocol
"	O
or	O
"	O
DFZ	O
"	O
)	O
.	O
</s>
<s>
Peering	B-Protocol
involves	O
two	O
networks	B-Architecture
coming	O
together	O
to	O
exchange	O
traffic	O
with	O
each	O
other	O
freely	O
,	O
and	O
for	O
mutual	O
benefit	O
.	O
</s>
<s>
This	O
'	O
mutual	O
benefit	O
 '	O
is	O
most	O
often	O
the	O
motivation	O
behind	O
peering	B-Protocol
,	O
which	O
is	O
often	O
described	O
solely	O
by	O
"	O
reduced	O
costs	O
for	O
transit	B-Application
services	O
"	O
.	O
</s>
<s>
Increased	O
redundancy	O
(	O
by	O
reducing	O
dependence	O
on	O
one	O
or	O
more	O
transit	B-Application
providers	I-Application
)	O
.	O
</s>
<s>
Increased	O
capacity	O
for	O
extremely	O
large	O
amounts	O
of	O
traffic	O
(	O
distributing	O
traffic	O
across	O
many	O
networks	B-Architecture
)	O
.	O
</s>
<s>
Increased	O
routing	B-Protocol
control	O
over	O
one	O
's	O
traffic	O
.	O
</s>
<s>
The	O
physical	O
interconnections	O
used	O
for	O
peering	B-Protocol
are	O
categorized	O
into	O
two	O
types	O
:	O
</s>
<s>
Public	O
peering	B-Protocol
–	O
Interconnection	O
utilizing	O
a	O
multi-party	O
shared	O
switch	O
fabric	O
such	O
as	O
an	O
Ethernet	O
switch	O
.	O
</s>
<s>
Private	O
peering	B-Protocol
–	O
Interconnection	O
utilizing	O
a	O
point-to-point	O
link	O
between	O
two	O
parties	O
.	O
</s>
<s>
Public	O
peering	B-Protocol
is	O
accomplished	O
across	O
a	O
Layer	B-Protocol
2	I-Protocol
access	O
technology	O
,	O
generally	O
called	O
a	O
shared	O
fabric	O
.	O
</s>
<s>
Historically	O
,	O
public	O
peering	B-Protocol
locations	O
were	O
known	O
as	O
network	O
access	O
points	O
(	O
NAPs	O
)	O
.	O
</s>
<s>
Today	O
they	O
are	O
most	O
often	O
called	O
exchange	B-Protocol
points	I-Protocol
or	O
Internet	B-Protocol
exchanges	I-Protocol
(	O
"	O
IXP	B-Protocol
"	O
)	O
.	O
</s>
<s>
Many	O
of	O
the	O
largest	O
exchange	B-Protocol
points	I-Protocol
in	O
the	O
world	O
can	O
have	O
hundreds	O
of	O
participants	O
,	O
and	O
some	O
span	O
multiple	O
buildings	O
and	O
colocation	B-Application
facilities	I-Application
across	O
a	O
city	O
.	O
</s>
<s>
Since	O
public	O
peering	B-Protocol
allows	O
networks	B-Architecture
interested	O
in	O
peering	B-Protocol
to	O
interconnect	O
with	O
many	O
other	O
networks	B-Architecture
through	O
a	O
single	O
port	O
,	O
it	O
is	O
often	O
considered	O
to	O
offer	O
"	O
less	O
capacity	O
"	O
than	O
private	O
peering	B-Protocol
,	O
but	O
to	O
a	O
larger	O
number	O
of	O
networks	B-Architecture
.	O
</s>
<s>
Many	O
smaller	O
networks	B-Architecture
,	O
or	O
networks	B-Architecture
which	O
are	O
just	O
beginning	O
to	O
peer	O
,	O
find	O
that	O
public	O
peering	B-Protocol
exchange	B-Protocol
points	I-Protocol
provide	O
an	O
excellent	O
way	O
to	O
meet	O
and	O
interconnect	O
with	O
other	O
networks	B-Architecture
which	O
may	O
be	O
open	O
to	O
peering	B-Protocol
with	O
them	O
.	O
</s>
<s>
Some	O
larger	O
networks	B-Architecture
utilize	O
public	O
peering	B-Protocol
as	O
a	O
way	O
to	O
aggregate	O
a	O
large	O
number	O
of	O
"	O
smaller	O
peers	O
"	O
,	O
or	O
as	O
a	O
location	O
for	O
conducting	O
low-cost	O
"	O
trial	O
peering	B-Protocol
"	O
without	O
the	O
expense	O
of	O
provisioning	O
private	O
peering	B-Protocol
on	O
a	O
temporary	O
basis	O
,	O
while	O
other	O
larger	O
networks	B-Architecture
are	O
not	O
willing	O
to	O
participate	O
at	O
public	O
exchanges	O
at	O
all	O
.	O
</s>
<s>
A	O
few	O
exchange	B-Protocol
points	I-Protocol
,	O
particularly	O
in	O
the	O
United	O
States	O
,	O
are	O
operated	O
by	O
commercial	O
carrier-neutral	O
third	O
parties	O
,	O
which	O
are	O
critical	O
for	O
achieving	O
cost-effective	O
data	B-Operating_System
center	I-Operating_System
connectivity	O
.	O
</s>
<s>
Private	O
peering	B-Protocol
is	O
the	O
direct	O
interconnection	O
between	O
only	O
two	O
networks	B-Architecture
,	O
across	O
a	O
Layer	O
1	O
or	O
2	O
medium	O
that	O
offers	O
dedicated	O
capacity	O
that	O
is	O
not	O
shared	O
by	O
any	O
other	O
parties	O
.	O
</s>
<s>
Early	O
in	O
the	O
history	O
of	O
the	O
Internet	O
,	O
many	O
private	O
peers	O
occurred	O
across	O
"	O
telco	O
"	O
provisioned	O
SONET	B-Protocol
circuits	O
between	O
individual	O
carrier-owned	O
facilities	O
.	O
</s>
<s>
Today	O
,	O
most	O
private	O
interconnections	O
occur	O
at	O
carrier	B-Application
hotels	I-Application
or	O
carrier	O
neutral	O
colocation	B-Application
facilities	I-Application
,	O
where	O
a	O
direct	O
crossconnect	O
can	O
be	O
provisioned	O
between	O
participants	O
within	O
the	O
same	O
building	O
,	O
usually	O
for	O
a	O
much	O
lower	O
cost	O
than	O
telco	O
circuits	O
.	O
</s>
<s>
Most	O
of	O
the	O
traffic	O
on	O
the	O
Internet	O
,	O
especially	O
traffic	O
between	O
the	O
largest	O
networks	B-Architecture
,	O
occurs	O
via	O
private	O
peering	B-Protocol
.	O
</s>
<s>
However	O
,	O
because	O
of	O
the	O
resources	O
required	O
to	O
provision	O
each	O
private	O
peer	O
,	O
many	O
networks	B-Architecture
are	O
unwilling	O
to	O
provide	O
private	O
peering	B-Protocol
to	O
"	O
small	O
"	O
networks	B-Architecture
,	O
or	O
to	O
"	O
new	O
"	O
networks	B-Architecture
which	O
have	O
not	O
yet	O
proven	O
that	O
they	O
will	O
provide	O
a	O
mutual	O
benefit	O
.	O
</s>
<s>
Such	O
agreements	O
set	O
forth	O
the	O
details	O
of	O
how	O
traffic	O
is	O
to	O
be	O
exchanged	O
,	O
along	O
with	O
a	O
list	O
of	O
expected	O
activities	O
which	O
may	O
be	O
necessary	O
to	O
maintain	O
the	O
peering	B-Protocol
relationship	O
,	O
a	O
list	O
of	O
activities	O
which	O
may	O
be	O
considered	O
abusive	O
and	O
result	O
in	O
termination	O
of	O
the	O
relationship	O
,	O
and	O
details	O
concerning	O
how	O
the	O
relationship	O
can	O
be	O
terminated	O
.	O
</s>
<s>
As	O
of	O
2011	O
,	O
such	O
contracts	O
account	O
for	O
less	O
than	O
0.5	O
%	O
of	O
all	O
peering	B-Protocol
agreements	O
.	O
</s>
<s>
By	O
definition	O
,	O
peering	B-Protocol
is	O
the	O
voluntary	O
and	O
free	O
exchange	O
of	O
traffic	O
between	O
two	O
networks	B-Architecture
,	O
for	O
mutual	O
benefit	O
.	O
</s>
<s>
If	O
one	O
or	O
both	O
networks	B-Architecture
believes	O
that	O
there	O
is	O
no	O
longer	O
a	O
mutual	O
benefit	O
,	O
they	O
may	O
decide	O
to	O
cease	O
peering	B-Protocol
:	O
this	O
is	O
known	O
as	O
depeering	O
.	O
</s>
<s>
A	O
desire	O
that	O
the	O
other	O
network	O
pay	O
settlement	O
,	O
either	O
in	O
exchange	O
for	O
continued	O
peering	B-Protocol
or	O
for	O
transit	B-Application
services	O
.	O
</s>
<s>
A	O
desire	O
to	O
peer	O
with	O
the	O
upstream	O
transit	B-Application
provider	I-Application
of	O
the	O
peered	O
network	O
.	O
</s>
<s>
Abuse	O
of	O
the	O
interconnection	O
by	O
the	O
other	O
party	O
,	O
such	O
as	O
pointing	O
default	O
or	O
utilizing	O
the	O
peer	O
for	O
transit	B-Application
.	O
</s>
<s>
Instability	O
of	O
the	O
peered	O
network	O
,	O
repeated	O
routing	B-Protocol
leaks	O
,	O
lack	O
of	O
response	O
to	O
network	O
abuse	O
issues	O
,	O
etc	O
.	O
</s>
<s>
The	O
inability	O
or	O
unwillingness	O
of	O
the	O
peered	O
network	O
to	O
provision	O
additional	O
capacity	O
for	O
peering	B-Protocol
.	O
</s>
<s>
The	O
belief	O
that	O
the	O
peered	O
network	O
is	O
unduly	O
peering	B-Protocol
with	O
one	O
's	O
customers	O
.	O
</s>
<s>
In	O
some	O
situations	O
,	O
networks	B-Architecture
which	O
are	O
being	O
depeered	O
have	O
been	O
known	O
to	O
attempt	O
to	O
fight	O
to	O
keep	O
the	O
peering	B-Protocol
by	O
intentionally	O
breaking	O
the	O
connectivity	O
between	O
the	O
two	O
networks	B-Architecture
when	O
the	O
peer	O
is	O
removed	O
,	O
either	O
through	O
a	O
deliberate	O
act	O
or	O
an	O
act	O
of	O
omission	O
.	O
</s>
<s>
The	O
goal	O
is	O
to	O
force	O
the	O
depeering	O
network	O
to	O
have	O
so	O
many	O
customer	O
complaints	O
that	O
they	O
are	O
willing	O
to	O
restore	O
peering	B-Protocol
.	O
</s>
<s>
The	O
"	O
donut	O
peering	B-Protocol
"	O
model	O
describes	O
the	O
intensive	O
interconnection	O
of	O
small	O
and	O
medium-sized	O
regional	O
networks	B-Architecture
that	O
make	O
up	O
much	O
of	O
the	O
Internet	O
.	O
</s>
<s>
Traffic	O
between	O
these	O
regional	O
networks	B-Architecture
can	O
be	O
modeled	O
as	O
a	O
toroid	O
,	O
with	O
a	O
core	O
"	O
donut	O
hole	O
"	O
that	O
is	O
poorly	O
interconnected	O
to	O
the	O
networks	B-Architecture
around	O
it	O
.	O
</s>
<s>
As	O
detailed	O
above	O
,	O
some	O
carriers	O
attempted	O
to	O
form	O
a	O
cartel	O
of	O
self-described	O
Tier	B-Architecture
1	I-Architecture
networks	I-Architecture
,	O
nominally	O
refusing	O
to	O
peer	O
with	O
any	O
networks	B-Architecture
outside	O
the	O
oligopoly	O
.	O
</s>
<s>
Seeking	O
to	O
reduce	O
transit	B-Application
costs	O
,	O
connections	O
between	O
regional	O
networks	B-Architecture
bypass	O
those	O
"	O
core	O
"	O
networks	B-Architecture
.	O
</s>
<s>
Data	O
takes	O
a	O
more	O
direct	O
path	O
,	O
reducing	O
latency	B-Protocol
and	O
packet	B-Protocol
loss	I-Protocol
.	O
</s>
<s>
This	O
also	O
improves	O
resiliency	O
between	O
consumers	O
and	O
content	O
providers	O
via	O
multiple	O
connections	O
in	O
many	O
locations	O
around	O
the	O
world	O
,	O
in	O
particular	O
during	O
business	O
disputes	O
between	O
the	O
core	O
transit	B-Application
providers	I-Application
.	O
</s>
<s>
The	O
majority	O
of	O
BGP	B-Protocol
AS-AS	O
adjacencies	O
are	O
the	O
product	O
of	O
multilateral	O
peering	B-Protocol
agreements	O
,	O
or	O
MLPAs	O
.	O
</s>
<s>
In	O
multilateral	O
peering	B-Protocol
,	O
an	O
unlimited	O
number	O
of	O
parties	O
agree	O
to	O
exchange	O
traffic	O
on	O
common	O
terms	O
,	O
using	O
a	O
single	O
agreement	O
to	O
which	O
they	O
each	O
accede	O
.	O
</s>
<s>
The	O
multilateral	O
peering	B-Protocol
is	O
typically	O
technically	O
instantiated	O
in	O
a	O
route	O
server	O
or	O
route	O
reflector	O
(	O
which	O
differ	O
from	O
looking	B-Application
glasses	I-Application
in	O
that	O
they	O
serve	O
routes	O
back	O
out	O
to	O
participants	O
,	O
rather	O
than	O
just	O
listening	O
to	O
inbound	O
routes	O
)	O
to	O
redistribute	O
routes	O
via	O
a	O
BGP	B-Protocol
hub-and-spoke	O
topology	O
,	O
rather	O
than	O
a	O
partial-mesh	O
topology	O
.	O
</s>
<s>
The	O
two	O
primary	O
criticisms	O
of	O
multilateral	O
peering	B-Protocol
are	O
that	O
it	O
breaks	O
the	O
shared	O
fate	O
of	O
the	O
forwarding	O
and	O
routing	B-Protocol
planes	O
,	O
since	O
the	O
layer-2	B-Protocol
connection	O
between	O
two	O
participants	O
could	O
hypothetically	O
fail	O
while	O
their	O
layer-2	B-Protocol
connections	O
with	O
the	O
route	O
server	O
remained	O
up	O
,	O
and	O
that	O
they	O
force	O
all	O
participants	O
to	O
treat	O
each	O
other	O
with	O
the	O
same	O
,	O
undifferentiated	O
,	O
routing	B-Protocol
policy	O
.	O
</s>
<s>
The	O
primary	O
benefit	O
of	O
multilateral	O
peering	B-Protocol
is	O
that	O
it	O
minimizes	O
configuration	O
for	O
each	O
peer	O
,	O
while	O
maximizing	O
the	O
efficiency	O
with	O
which	O
new	O
peers	O
can	O
begin	O
contributing	O
routes	O
to	O
the	O
exchange	O
.	O
</s>
<s>
While	O
optional	O
multilateral	O
peering	B-Protocol
agreements	O
and	O
route	O
servers	O
are	O
now	O
widely	O
acknowledged	O
to	O
be	O
a	O
good	O
practice	O
,	O
mandatory	O
multilateral	O
peering	B-Protocol
agreements	O
(	O
MMLPAs	O
)	O
have	O
long	O
been	O
agreed	O
to	O
not	O
be	O
a	O
good	O
practice	O
.	O
</s>
<s>
The	O
modern	O
Internet	O
operates	O
with	O
significantly	O
more	O
peering	B-Protocol
locations	O
than	O
at	O
any	O
time	O
in	O
the	O
past	O
,	O
resulting	O
in	O
improved	O
performance	O
and	O
better	O
routing	B-Protocol
for	O
the	O
majority	O
of	O
the	O
traffic	O
on	O
the	O
Internet	O
.	O
</s>
<s>
However	O
,	O
in	O
the	O
interests	O
of	O
reducing	O
costs	O
and	O
improving	O
efficiency	O
,	O
most	O
networks	B-Architecture
have	O
attempted	O
to	O
standardize	O
on	O
relatively	O
few	O
locations	O
within	O
these	O
individual	O
regions	O
where	O
they	O
will	O
be	O
able	O
to	O
quickly	O
and	O
efficiently	O
interconnect	O
with	O
their	O
peering	B-Protocol
partners	O
.	O
</s>
<s>
As	O
of	O
2021	O
,	O
the	O
largest	O
exchange	B-Protocol
points	I-Protocol
in	O
the	O
world	O
are	O
Ponto	O
de	O
Troca	O
de	O
Tráfego	O
Metro	O
São	O
Paulo	O
,	O
in	O
São	O
Paulo	O
,	O
with	O
2,289	O
peering	B-Protocol
networks	B-Architecture
;	O
OpenIXP	O
in	O
Jakarta	O
,	O
with	O
1,097	O
peering	B-Protocol
networks	B-Architecture
;	O
and	O
DE-CIX	O
in	O
Frankfurt	O
,	O
with	O
1,050	O
peering	B-Protocol
networks	B-Architecture
.	O
</s>
<s>
The	O
United	O
States	O
,	O
with	O
a	O
historically	O
larger	O
focus	O
on	O
private	O
peering	B-Protocol
and	O
commercial	O
public	O
peering	B-Protocol
,	O
has	O
much	O
less	O
traffic	O
visible	O
on	O
public	O
peering	B-Protocol
switch-fabrics	O
compared	O
to	O
other	O
regions	O
that	O
are	O
dominated	O
by	O
non-profit	O
membership	O
exchange	B-Protocol
points	I-Protocol
.	O
</s>
<s>
Collectively	O
,	O
the	O
many	O
exchange	B-Protocol
points	I-Protocol
operated	O
by	O
Equinix	O
are	O
generally	O
considered	O
to	O
be	O
the	O
largest	O
,	O
though	O
traffic	O
figures	O
are	O
not	O
generally	O
published	O
.	O
</s>
<s>
Other	O
important	O
but	O
smaller	O
exchange	B-Protocol
points	I-Protocol
include	O
AMS-IX	O
in	O
Amsterdam	O
,	O
LINX	O
and	O
LONAP	O
in	O
London	O
,	O
and	O
NYIIX	O
in	O
New	O
York	O
.	O
</s>
<s>
URLs	O
to	O
some	O
public	O
traffic	O
statistics	O
of	O
exchange	B-Protocol
points	I-Protocol
include	O
:	O
</s>
<s>
A	O
great	O
deal	O
of	O
the	O
complexity	O
in	O
the	O
BGP	B-Protocol
routing	B-Protocol
protocol	O
exists	O
to	O
aid	O
the	O
enforcement	O
and	O
fine-tuning	O
of	O
peering	B-Protocol
and	O
transit	B-Application
agreements	O
.	O
</s>
<s>
BGP	B-Protocol
allows	O
operators	O
to	O
define	O
a	O
policy	O
that	O
determines	O
where	O
traffic	O
is	O
routed	B-Protocol
.	O
</s>
<s>
Three	O
things	O
commonly	O
used	O
to	O
determine	O
routing	B-Protocol
are	O
local-preference	O
,	O
multi	O
exit	O
discriminators	O
(	O
MEDs	O
)	O
and	O
AS-Path	O
.	O
</s>
<s>
Local-preference	O
is	O
used	O
internally	O
within	O
a	O
network	O
to	O
differentiate	O
classes	O
of	O
networks	B-Architecture
.	O
</s>
<s>
Settlement	O
free	O
peering	B-Protocol
is	O
then	O
configured	O
to	O
be	O
preferred	O
over	O
paid	O
IP	B-Application
transit	I-Application
.	O
</s>
<s>
Networks	B-Architecture
that	O
speak	O
BGP	B-Protocol
to	O
each	O
other	O
can	O
engage	O
in	O
multi	O
exit	O
discriminator	O
exchange	O
with	O
each	O
other	O
,	O
although	O
most	O
do	O
not	O
.	O
</s>
<s>
When	O
networks	B-Architecture
interconnect	O
in	O
several	O
locations	O
,	O
MEDs	O
can	O
be	O
used	O
to	O
reference	O
that	O
network	O
's	O
interior	B-Protocol
gateway	I-Protocol
protocol	I-Protocol
cost	O
.	O
</s>
<s>
This	O
results	O
in	O
both	O
networks	B-Architecture
sharing	O
the	O
burden	O
of	O
transporting	O
each	O
other	O
's	O
traffic	O
on	O
their	O
own	O
network	O
(	O
or	O
cold	B-Protocol
potato	I-Protocol
)	O
.	O
</s>
<s>
Hot-potato	B-Protocol
or	O
nearest-exit	O
routing	B-Protocol
,	O
which	O
is	O
typically	O
the	O
normal	O
behavior	O
on	O
the	O
Internet	O
,	O
is	O
where	O
traffic	O
destined	O
to	O
another	O
network	O
is	O
delivered	O
to	O
the	O
closest	O
interconnection	O
point	O
.	O
</s>
<s>
In	O
2001	O
,	O
the	O
Federal	O
Communications	O
Commission	O
's	O
advisory	O
committee	O
,	O
the	O
Network	O
Reliability	O
and	O
Interoperability	O
Council	O
recommended	O
that	O
Internet	O
backbones	O
publish	O
their	O
peering	B-Protocol
policies	O
,	O
something	O
that	O
they	O
had	O
been	O
hesitant	O
to	O
do	O
beforehand	O
.	O
</s>
<s>
In	O
the	O
ICAIS	O
debate	O
,	O
countries	O
underserved	O
by	O
Internet	O
backbones	O
have	O
complained	O
that	O
it	O
is	O
unfair	O
that	O
they	O
must	O
pay	O
the	O
full	O
cost	O
of	O
connecting	O
to	O
an	O
Internet	B-Protocol
exchange	I-Protocol
point	I-Protocol
in	O
a	O
different	O
country	O
,	O
frequently	O
the	O
United	O
States	O
.	O
</s>
<s>
Those	O
who	O
argue	O
against	O
ICAIS	O
point	O
out	O
that	O
much	O
of	O
the	O
problem	O
would	O
be	O
solved	O
by	O
building	O
local	O
exchange	B-Protocol
points	I-Protocol
.	O
</s>
<s>
A	O
significant	O
amount	O
of	O
the	O
traffic	O
,	O
it	O
is	O
argued	O
,	O
that	O
is	O
brought	O
to	O
the	O
US	O
and	O
exchanged	O
then	O
leaves	O
the	O
US	O
,	O
using	O
US	O
exchange	B-Protocol
points	I-Protocol
as	O
switching	O
offices	O
but	O
not	O
terminating	O
in	O
the	O
US	O
.	O
</s>
