<s>
Convergence	B-Protocol
is	O
the	O
state	O
of	O
a	O
set	O
of	O
routers	B-Protocol
that	O
have	O
the	O
same	O
topological	B-Architecture
information	O
about	O
the	O
internetwork	B-Architecture
in	O
which	O
they	O
operate	O
.	O
</s>
<s>
For	O
a	O
set	O
of	O
routers	B-Protocol
to	O
have	O
converged	O
,	O
they	O
must	O
have	O
collected	O
all	O
available	O
topology	B-Architecture
information	O
from	O
each	O
other	O
via	O
the	O
implemented	O
routing	B-Protocol
protocol	I-Protocol
,	O
the	O
information	O
they	O
gathered	O
must	O
not	O
contradict	O
any	O
other	O
router	B-Protocol
's	O
topology	B-Architecture
information	O
in	O
the	O
set	O
,	O
and	O
it	O
must	O
reflect	O
the	O
real	O
state	O
of	O
the	O
network	O
.	O
</s>
<s>
In	O
other	O
words	O
:	O
in	O
a	O
converged	O
network	O
all	O
routers	B-Protocol
"	O
agree	O
"	O
on	O
what	O
the	O
network	B-Architecture
topology	I-Architecture
looks	O
like	O
.	O
</s>
<s>
Convergence	B-Protocol
is	O
an	O
important	O
notion	O
for	O
a	O
set	O
of	O
routers	B-Protocol
that	O
engage	O
in	O
dynamic	B-Protocol
routing	I-Protocol
.	O
</s>
<s>
All	O
Interior	B-Protocol
Gateway	I-Protocol
Protocols	I-Protocol
rely	O
on	O
convergence	B-Protocol
to	O
function	O
properly	O
.	O
</s>
<s>
"	O
To	O
have	O
,	O
or	O
be	O
,	O
converged	O
"	O
is	O
the	O
normal	O
state	O
of	O
an	O
operational	O
autonomous	B-Architecture
system	I-Architecture
.	O
</s>
<s>
The	O
Exterior	O
Gateway	O
Routing	B-Protocol
Protocol	I-Protocol
BGP	B-Protocol
typically	O
never	O
converges	O
because	O
the	O
Internet	O
is	O
too	O
big	O
for	O
changes	O
to	O
be	O
communicated	O
fast	O
enough	O
.	O
</s>
<s>
When	O
a	O
routing	B-Protocol
protocol	I-Protocol
process	O
is	O
enabled	O
,	O
every	O
participating	O
router	B-Protocol
will	O
attempt	O
to	O
exchange	O
information	O
about	O
the	O
topology	B-Architecture
of	O
the	O
network	O
.	O
</s>
<s>
The	O
extent	O
of	O
this	O
information	O
exchange	O
,	O
the	O
way	O
it	O
is	O
sent	O
and	O
received	O
,	O
and	O
the	O
type	O
of	O
information	O
required	O
vary	O
widely	O
depending	O
on	O
the	O
routing	B-Protocol
protocol	I-Protocol
in	O
use	O
,	O
see	O
e.g.	O
</s>
<s>
RIP	B-Protocol
,	O
OSPF	B-Protocol
,	O
BGP4	B-Protocol
.	O
</s>
<s>
A	O
state	O
of	O
convergence	B-Protocol
is	O
achieved	O
once	O
all	O
routing	O
protocol-specific	O
information	O
has	O
been	O
distributed	O
to	O
all	O
routers	B-Protocol
participating	O
in	O
the	O
routing	B-Protocol
protocol	I-Protocol
process	O
.	O
</s>
<s>
Any	O
change	O
in	O
the	O
network	O
that	O
affects	O
routing	B-Protocol
tables	I-Protocol
will	O
break	O
the	O
convergence	B-Protocol
temporarily	O
until	O
this	O
change	O
has	O
been	O
successfully	O
communicated	O
to	O
all	O
other	O
routers	B-Protocol
.	O
</s>
<s>
Convergence	B-Protocol
time	O
is	O
a	O
measure	O
of	O
how	O
fast	O
a	O
group	O
of	O
routers	B-Protocol
reach	O
the	O
state	O
of	O
convergence	B-Protocol
.	O
</s>
<s>
It	O
is	O
one	O
of	O
the	O
main	O
design	O
goals	O
and	O
an	O
important	O
performance	O
indicator	O
for	O
routing	B-Protocol
protocols	I-Protocol
,	O
which	O
should	O
implement	O
a	O
mechanism	O
that	O
allows	O
all	O
routers	B-Protocol
running	O
the	O
protocol	O
to	O
quickly	O
and	O
reliably	O
converge	O
.	O
</s>
<s>
RIP	B-Protocol
is	O
a	O
routing	B-Protocol
protocol	I-Protocol
that	O
converges	O
so	O
slowly	O
that	O
even	O
a	O
network	O
of	O
a	O
few	O
routers	B-Protocol
can	O
take	O
a	O
couple	O
of	O
minutes	O
to	O
converge	O
.	O
</s>
<s>
In	O
case	O
of	O
a	O
new	O
route	O
being	O
advertised	O
,	O
triggered	O
updates	O
can	O
speed	O
up	O
RIP	B-Protocol
's	O
convergence	B-Protocol
but	O
to	O
flush	O
a	O
route	O
that	O
previously	O
existed	O
takes	O
longer	O
due	O
to	O
the	O
holddown	B-Protocol
timers	I-Protocol
in	O
use	O
.	O
</s>
<s>
OSPF	B-Protocol
is	O
an	O
example	O
of	O
a	O
fast-converging	O
routing	B-Protocol
protocol	I-Protocol
.	O
</s>
<s>
A	O
network	O
of	O
a	O
few	O
OSPF	B-Protocol
routers	B-Protocol
can	O
converge	O
in	O
a	O
matter	O
of	O
seconds	O
.	O
</s>
<s>
For	O
instance	O
,	O
a	O
"	O
flapping	B-Protocol
"	O
interface	O
(	O
an	O
interface	O
that	O
frequently	O
changes	O
its	O
state	O
between	O
"	O
up	O
"	O
and	O
"	O
down	O
"	O
)	O
might	O
cause	O
conflicting	O
information	O
to	O
propagate	O
throughout	O
the	O
network	O
so	O
the	O
routers	B-Protocol
never	O
agree	O
on	O
its	O
current	O
state	O
.	O
</s>
<s>
Under	O
certain	O
circumstances	O
it	O
might	O
be	O
desirable	O
to	O
withhold	O
detailed	O
routing	B-Protocol
information	I-Protocol
from	O
parts	O
of	O
the	O
network	O
via	O
route	B-Protocol
aggregation	I-Protocol
,	O
thereby	O
speeding	O
up	O
convergence	B-Protocol
of	O
the	O
topological	B-Architecture
information	O
shared	O
by	O
all	O
routers	B-Protocol
.	O
</s>
