<s>
Enhanced	B-Protocol
Interior	I-Protocol
Gateway	I-Protocol
Routing	I-Protocol
Protocol	I-Protocol
(	O
EIGRP	B-Protocol
)	O
is	O
an	O
advanced	O
distance-vector	B-Protocol
routing	I-Protocol
protocol	I-Protocol
that	O
is	O
used	O
on	O
a	O
computer	B-Architecture
network	I-Architecture
for	O
automating	O
routing	B-Protocol
decisions	O
and	O
configuration	O
.	O
</s>
<s>
The	O
protocol	O
was	O
designed	O
by	O
Cisco	O
Systems	O
as	O
a	O
proprietary	O
protocol	O
,	O
available	O
only	O
on	O
Cisco	O
routers	B-Protocol
.	O
</s>
<s>
In	O
2013	O
Cisco	O
decided	O
to	O
allow	O
other	O
vendors	O
freely	O
implement	O
limited	O
version	O
of	O
EIGRP	B-Protocol
with	O
some	O
of	O
its	O
associated	O
features	O
such	O
as	O
High	O
Availability	O
(	O
HA	O
)	O
,	O
while	O
withholding	O
other	O
EIGRP	B-Protocol
features	O
such	O
as	O
EIGRP	B-Protocol
stub	O
,	O
needed	O
for	O
DMVPN	O
and	O
large-scale	O
campus	O
deployment	O
,	O
exclusively	O
for	O
themselves	O
.	O
</s>
<s>
Information	O
needed	O
for	O
implementation	O
was	O
published	O
with	O
informational	O
status	O
as	O
in	O
2016	O
,	O
which	O
did	O
not	O
make	O
it	O
into	O
an	O
Internet	O
Standards	O
Track	O
specification	O
and	O
allowed	O
Cisco	O
to	O
retain	O
control	O
of	O
the	O
EIGRP	B-Protocol
protocol	O
.	O
</s>
<s>
EIGRP	B-Protocol
is	O
used	O
on	O
a	O
router	B-Protocol
to	O
share	O
routes	O
with	O
other	O
routers	B-Protocol
within	O
the	O
same	O
autonomous	B-Architecture
system	I-Architecture
.	O
</s>
<s>
Unlike	O
other	O
well	O
known	O
routing	B-Protocol
protocols	I-Protocol
,	O
such	O
as	O
RIP	B-Protocol
,	O
EIGRP	B-Protocol
only	O
sends	O
incremental	O
updates	O
,	O
reducing	O
the	O
workload	O
on	O
the	O
router	B-Protocol
and	O
the	O
amount	O
of	O
data	O
that	O
needs	O
to	O
be	O
transmitted	O
.	O
</s>
<s>
EIGRP	B-Protocol
replaced	O
the	O
Interior	B-Protocol
Gateway	I-Protocol
Routing	I-Protocol
Protocol	I-Protocol
(	O
IGRP	B-Protocol
)	O
in	O
1993	O
.	O
</s>
<s>
One	O
of	O
the	O
major	O
reasons	O
for	O
this	O
was	O
the	O
change	O
to	O
classless	B-Protocol
IPv4	O
addresses	O
in	O
the	O
Internet	B-Protocol
Protocol	I-Protocol
,	O
which	O
IGRP	B-Protocol
could	O
not	O
support	O
.	O
</s>
<s>
Almost	O
all	O
routers	B-Protocol
contain	O
a	O
routing	B-Protocol
table	I-Protocol
that	O
contains	O
rules	O
by	O
which	O
traffic	O
is	O
forwarded	O
in	O
a	O
network	O
.	O
</s>
<s>
If	O
the	O
router	B-Protocol
does	O
not	O
contain	O
a	O
valid	O
path	O
to	O
the	O
destination	O
,	O
the	O
traffic	O
is	O
discarded	O
.	O
</s>
<s>
EIGRP	B-Protocol
is	O
a	O
dynamic	B-Protocol
routing	I-Protocol
protocol	O
by	O
which	O
routers	B-Protocol
automatically	O
share	O
route	O
information	O
.	O
</s>
<s>
This	O
eases	O
the	O
workload	O
on	O
a	O
network	O
administrator	O
who	O
does	O
not	O
have	O
to	O
configure	O
changes	O
to	O
the	O
routing	B-Protocol
table	I-Protocol
manually	O
.	O
</s>
<s>
In	O
addition	O
to	O
the	O
routing	B-Protocol
table	I-Protocol
,	O
EIGRP	B-Protocol
uses	O
the	O
following	O
tables	O
to	O
store	O
information	O
:	O
</s>
<s>
Neighbor	O
Table	O
:	O
The	O
neighbor	O
table	O
keeps	O
a	O
record	O
of	O
the	O
IP	B-Protocol
addresses	I-Protocol
of	O
routers	B-Protocol
that	O
have	O
a	O
direct	O
physical	O
connection	O
with	O
this	O
router	B-Protocol
.	O
</s>
<s>
Routers	B-Protocol
that	O
are	O
connected	O
to	O
this	O
router	B-Protocol
indirectly	O
,	O
through	O
another	O
router	B-Protocol
,	O
are	O
not	O
recorded	O
in	O
this	O
table	O
as	O
they	O
are	O
not	O
considered	O
neighbors	O
.	O
</s>
<s>
Topology	O
Table	O
:	O
The	O
topology	O
table	O
stores	O
routes	O
that	O
it	O
has	O
learned	O
from	O
neighbor	O
routing	B-Protocol
tables	I-Protocol
.	O
</s>
<s>
Unlike	O
a	O
routing	B-Protocol
table	I-Protocol
,	O
the	O
topology	O
table	O
does	O
not	O
store	O
all	O
routes	O
,	O
but	O
only	O
routes	O
that	O
have	O
been	O
determined	O
by	O
EIGRP	B-Protocol
.	O
</s>
<s>
The	O
topology	O
table	O
also	O
records	O
the	O
metrics	O
for	O
each	O
of	O
the	O
listed	O
EIGRP	B-Protocol
routes	O
,	O
the	O
feasible	O
successor	O
and	O
the	O
successors	O
.	O
</s>
<s>
Passive	O
indicates	O
that	O
EIGRP	B-Protocol
has	O
determined	O
the	O
path	O
for	O
the	O
specific	O
route	O
and	O
has	O
finished	O
processing	O
.	O
</s>
<s>
Active	O
indicates	O
that	O
EIGRP	B-Protocol
is	O
still	O
trying	O
to	O
calculate	O
the	O
best	O
path	O
for	O
the	O
specific	O
route	O
.	O
</s>
<s>
Routes	O
in	O
the	O
topology	O
table	O
are	O
not	O
usable	B-General_Concept
by	O
the	O
router	B-Protocol
until	O
they	O
are	O
inserted	O
into	O
the	O
routing	B-Protocol
table	I-Protocol
.	O
</s>
<s>
The	O
topology	O
table	O
is	O
never	O
used	O
by	O
the	O
router	B-Protocol
to	O
forward	O
traffic	O
.	O
</s>
<s>
Routes	O
in	O
the	O
topology	O
table	O
will	O
not	O
be	O
inserted	O
into	O
the	O
routing	B-Protocol
table	I-Protocol
if	O
they	O
are	O
active	O
,	O
are	O
a	O
feasible	O
successor	O
,	O
or	O
have	O
a	O
higher	O
administrative	B-Protocol
distance	I-Protocol
than	O
an	O
equivalent	O
path	O
.	O
</s>
<s>
Information	O
in	O
the	O
topology	O
table	O
may	O
be	O
inserted	O
into	O
the	O
router	B-Protocol
's	O
routing	B-Protocol
table	I-Protocol
and	O
can	O
then	O
be	O
used	O
to	O
forward	O
traffic	O
.	O
</s>
<s>
EIGRP	B-Protocol
is	O
designed	O
to	O
detect	O
these	O
changes	O
and	O
will	O
attempt	O
to	O
find	O
a	O
new	O
path	O
to	O
the	O
destination	O
.	O
</s>
<s>
The	O
old	O
path	O
that	O
is	O
no	O
longer	O
available	O
is	O
removed	O
from	O
the	O
routing	B-Protocol
table	I-Protocol
.	O
</s>
<s>
Unlike	O
most	O
distance	B-Protocol
vector	I-Protocol
routing	I-Protocol
protocols	I-Protocol
,	O
EIGRP	B-Protocol
does	O
not	O
transmit	O
all	O
the	O
data	O
in	O
the	O
router	B-Protocol
's	O
routing	B-Protocol
table	I-Protocol
when	O
a	O
change	O
is	O
made	O
,	O
but	O
will	O
only	O
transmit	O
the	O
changes	O
that	O
have	O
been	O
made	O
since	O
the	O
routing	B-Protocol
table	I-Protocol
was	O
last	O
updated	O
.	O
</s>
<s>
EIGRP	B-Protocol
does	O
not	O
send	O
its	O
routing	B-Protocol
table	I-Protocol
periodically	O
,	O
but	O
will	O
only	O
send	O
routing	B-Protocol
table	I-Protocol
data	O
when	O
an	O
actual	O
change	O
has	O
occurred	O
.	O
</s>
<s>
This	O
behavior	O
is	O
more	O
inline	O
with	O
link-state	B-Protocol
routing	I-Protocol
protocols	I-Protocol
,	O
thus	O
EIGRP	B-Protocol
is	O
mostly	O
considered	O
a	O
hybrid	O
protocol	O
.	O
</s>
<s>
When	O
a	O
router	B-Protocol
running	O
EIGRP	B-Protocol
is	O
connected	O
to	O
another	O
router	B-Protocol
also	O
running	O
EIGRP	B-Protocol
,	O
information	O
is	O
exchanged	O
between	O
the	O
two	O
routers	B-Protocol
.	O
</s>
<s>
The	O
entire	O
routing	B-Protocol
table	I-Protocol
is	O
exchanged	O
between	O
both	O
routers	B-Protocol
at	O
this	O
time	O
.	O
</s>
<s>
EIGRP	B-Protocol
is	O
often	O
considered	O
a	O
hybrid	O
protocol	O
because	O
it	O
also	O
sends	O
link	B-Protocol
state	I-Protocol
updates	O
when	O
link	B-Protocol
states	I-Protocol
change	O
.	O
</s>
<s>
EIGRP	B-Protocol
supports	O
the	O
following	O
features	O
:	O
</s>
<s>
Support	O
for	O
Classless	B-Protocol
Inter-Domain	I-Protocol
Routing	I-Protocol
(	O
CIDR	B-Protocol
)	O
and	O
variable	O
length	O
subnet	B-Protocol
masking	O
.	O
</s>
<s>
Support	O
for	O
load	B-Application
balancing	I-Application
on	O
parallel	O
links	O
between	O
sites	O
.	O
</s>
<s>
MD5	B-Algorithm
and	O
SHA-2	B-Algorithm
authentication	O
between	O
two	O
routers	B-Protocol
.	O
</s>
<s>
Sends	O
topology	O
changes	O
,	O
rather	O
than	O
sending	O
the	O
entire	O
routing	B-Protocol
table	I-Protocol
when	O
a	O
route	O
is	O
changed	O
.	O
</s>
<s>
Periodically	O
checks	O
if	O
a	O
route	O
is	O
available	O
,	O
and	O
propagates	O
routing	B-Protocol
changes	O
to	O
neighboring	O
routers	B-Protocol
if	O
any	O
changes	O
have	O
occurred	O
.	O
</s>
<s>
Runs	O
separate	O
routing	B-Protocol
processes	O
for	O
Internet	B-Protocol
Protocol	I-Protocol
(	O
IP	O
)	O
,	O
IPv6	B-Protocol
,	O
IPX	B-Protocol
and	O
AppleTalk	B-Application
,	O
through	O
the	O
use	O
of	O
protocol-dependent	B-Protocol
modules	I-Protocol
(	O
PDMs	O
)	O
.	O
</s>
<s>
Backwards	O
compatibility	O
with	O
the	O
IGRP	B-Protocol
routing	B-Protocol
protocols	I-Protocol
.	O
</s>
<s>
Example	O
of	O
setting	O
up	O
EIGRP	B-Protocol
on	O
a	O
Cisco	O
IOS	O
router	B-Protocol
for	O
a	O
private	B-Protocol
network	I-Protocol
.	O
</s>
<s>
The	O
0.0.15.255	O
wildcard	B-Algorithm
in	O
this	O
example	O
indicates	O
a	O
subnetwork	B-Protocol
with	O
a	O
maximum	O
of	O
4094	O
hosts	O
—	O
it	O
is	O
the	O
bitwise	O
complement	O
of	O
the	O
subnet	B-Protocol
mask	I-Protocol
255.255.240.0	O
.	O
</s>
<s>
The	O
no	O
auto-summary	O
command	O
prevents	O
automatic	O
route	B-Protocol
summarization	I-Protocol
on	O
classful	O
boundaries	O
,	O
which	O
would	O
otherwise	O
result	O
in	O
routing	B-Protocol
loops	I-Protocol
in	O
discontiguous	O
networks	O
.	O
</s>
<s>
EIGRP	B-Protocol
is	O
a	O
distance	B-Protocol
vector	I-Protocol
&	O
Link	B-Protocol
State	I-Protocol
routing	I-Protocol
protocol	I-Protocol
that	O
uses	O
the	O
diffusing	B-Protocol
update	I-Protocol
algorithm	I-Protocol
(	O
DUAL	O
)	O
(	O
based	O
on	O
work	O
from	O
SRI	O
International	O
)	O
to	O
improve	O
the	O
efficiency	O
of	O
the	O
protocol	O
and	O
to	O
help	O
prevent	O
calculation	O
errors	O
when	O
attempting	O
to	O
determine	O
the	O
best	O
path	O
to	O
a	O
remote	O
network	O
.	O
</s>
<s>
EIGRP	B-Protocol
determines	O
the	O
value	O
of	O
the	O
path	O
using	O
five	O
metrics	O
:	O
bandwidth	O
,	O
load	O
,	O
delay	O
,	O
reliability	O
and	O
MTU	B-Protocol
.	O
</s>
<s>
EIGRP	B-Protocol
uses	O
five	O
different	O
messages	O
to	O
communicate	O
with	O
its	O
neighbor	O
routers	B-Protocol
.	O
</s>
<s>
EIGRP	B-Protocol
messages	O
are	O
Hello	O
,	O
Update	O
,	O
Query	O
,	O
Reply	O
,	O
and	O
Acknowledgement	O
.	O
</s>
<s>
EIGRP	B-Protocol
routing	B-Protocol
information	I-Protocol
exchanged	O
to	O
a	O
router	B-Protocol
from	O
another	O
router	B-Protocol
within	O
the	O
same	O
autonomous	B-Architecture
system	I-Architecture
has	O
a	O
default	O
administrative	B-Protocol
distance	I-Protocol
of	O
90	O
.	O
</s>
<s>
EIGRP	B-Protocol
routing	B-Protocol
information	I-Protocol
that	O
has	O
come	O
from	O
an	O
EIGRP-enabled	O
router	B-Protocol
outside	O
the	O
autonomous	B-Architecture
system	I-Architecture
has	O
a	O
default	O
administrative	B-Protocol
distance	I-Protocol
of	O
170	O
.	O
</s>
<s>
EIGRP	B-Protocol
does	O
not	O
operate	O
using	O
the	O
Transmission	B-Protocol
Control	I-Protocol
Protocol	I-Protocol
(	O
TCP	O
)	O
or	O
the	O
User	B-Protocol
Datagram	I-Protocol
Protocol	I-Protocol
(	O
UDP	O
)	O
.	O
</s>
<s>
This	O
means	O
that	O
EIGRP	B-Protocol
does	O
not	O
use	O
a	O
port	B-Protocol
number	I-Protocol
to	O
identify	O
traffic	O
.	O
</s>
<s>
Rather	O
,	O
EIGRP	B-Protocol
is	O
designed	O
to	O
work	O
on	O
top	O
of	O
layer	O
3	O
(	O
i.e.	O
</s>
<s>
the	O
IP	B-Protocol
protocol	I-Protocol
)	O
.	O
</s>
<s>
Since	O
EIGRP	B-Protocol
does	O
not	O
use	O
TCP	O
for	O
communication	O
,	O
it	O
implements	O
Cisco	O
's	O
Reliable	O
Transport	O
Protocol	O
(	O
RTP	O
)	O
to	O
ensure	O
that	O
EIGRP	B-Protocol
router	B-Protocol
updates	O
are	O
delivered	O
to	O
all	O
neighbors	O
completely	O
.	O
</s>
<s>
EIGRP	B-Protocol
uses	O
224.0.0.10	O
as	O
its	O
multicast	O
address	O
and	O
protocol	B-Protocol
number	I-Protocol
88	O
.	O
</s>
<s>
Cisco	O
Systems	O
now	O
classifies	O
EIGRP	B-Protocol
as	O
a	O
distance	B-Protocol
vector	I-Protocol
routing	I-Protocol
protocol	I-Protocol
,	O
but	O
it	O
is	O
normally	O
said	O
to	O
be	O
a	O
hybrid	O
routing	B-Protocol
protocol	I-Protocol
.	O
</s>
<s>
While	O
EIGRP	B-Protocol
is	O
an	O
advanced	O
routing	B-Protocol
protocol	I-Protocol
that	O
combines	O
many	O
of	O
the	O
features	O
of	O
both	O
link-state	B-Protocol
and	O
distance-vector	B-Protocol
routing	I-Protocol
protocols	I-Protocol
,	O
EIGRP	B-Protocol
's	O
DUAL	B-Protocol
algorithm	I-Protocol
contains	O
many	O
features	O
which	O
make	O
it	O
more	O
of	O
a	O
distance	B-Protocol
vector	I-Protocol
routing	I-Protocol
protocol	I-Protocol
than	O
a	O
link-state	B-Protocol
routing	I-Protocol
protocol	I-Protocol
.	O
</s>
<s>
Despite	O
this	O
,	O
EIGRP	B-Protocol
contains	O
many	O
differences	O
from	O
most	O
other	O
distance-vector	B-Protocol
routing	I-Protocol
protocols	I-Protocol
,	O
including	O
:	O
</s>
<s>
the	O
use	O
of	O
explicit	O
hello	O
packets	O
to	O
discover	O
and	O
maintain	O
adjacencies	O
between	O
routers	B-Protocol
.	O
</s>
<s>
the	O
use	O
of	O
a	O
reliable	O
protocol	O
to	O
transport	O
routing	B-Protocol
updates	O
.	O
</s>
<s>
EIGRP	B-Protocol
associates	O
six	O
different	O
vector	O
metrics	O
with	O
each	O
route	O
and	O
considers	O
only	O
four	O
of	O
the	O
vector	O
metrics	O
in	O
computing	O
the	O
Composite	O
metric	O
:	O
</s>
<s>
Routing	B-Protocol
Descriptor	O
Blocks	O
:	O
</s>
<s>
Bandwidth	O
Minimum	O
Bandwidth	O
(	O
in	O
kilobits	O
per	O
second	O
)	O
along	O
the	O
path	O
from	O
router	B-Protocol
to	O
destination	O
network	O
.	O
</s>
<s>
Hop	O
Count	O
Number	O
of	O
routers	B-Protocol
a	O
packet	O
passes	O
through	O
when	O
routing	B-Protocol
to	O
a	O
remote	O
network	O
,	O
used	O
to	O
limit	O
the	O
EIGRP	B-Protocol
AS	O
.	O
</s>
<s>
EIGRP	B-Protocol
maintains	O
a	O
hop	O
count	O
for	O
every	O
route	O
,	O
however	O
,	O
the	O
hop	O
count	O
is	O
not	O
used	O
in	O
metric	O
calculation	O
.	O
</s>
<s>
It	O
is	O
only	O
verified	O
against	O
a	O
predefined	O
maximum	O
on	O
an	O
EIGRP	B-Protocol
router	B-Protocol
(	O
by	O
default	O
it	O
is	O
set	O
to	O
100	O
and	O
can	O
be	O
changed	O
to	O
any	O
value	O
between	O
1	O
and	O
255	O
)	O
.	O
</s>
<s>
Routes	O
having	O
a	O
hop	O
count	O
higher	O
than	O
the	O
maximum	O
will	O
be	O
advertised	O
as	O
unreachable	O
by	O
an	O
EIGRP	B-Protocol
router	B-Protocol
.	O
</s>
<s>
The	O
composite	O
routing	B-Protocol
metric	O
calculation	O
uses	O
five	O
parameters	O
,	O
so-called	O
K	O
values	O
,	O
K1	O
through	O
K5	O
.	O
</s>
<s>
By	O
default	O
,	O
only	O
total	O
delay	O
and	O
minimum	O
bandwidth	O
are	O
considered	O
when	O
EIGRP	B-Protocol
is	O
started	O
on	O
a	O
router	B-Protocol
,	O
but	O
an	O
administrator	O
can	O
enable	O
or	O
disable	O
all	O
the	O
K	O
values	O
as	O
needed	O
to	O
consider	O
the	O
other	O
Vector	O
metrics	O
.	O
</s>
<s>
Obviously	O
,	O
these	O
constants	O
must	O
be	O
set	O
to	O
the	O
same	O
value	O
on	O
all	O
routers	B-Protocol
in	O
an	O
EIGRP	B-Protocol
system	O
,	O
or	O
permanent	O
routing	B-Protocol
loops	I-Protocol
may	O
result	O
.	O
</s>
<s>
Cisco	O
routers	B-Protocol
running	O
EIGRP	B-Protocol
will	O
not	O
form	O
an	O
EIGRP	B-Protocol
adjacency	O
and	O
will	O
complain	O
about	O
K-values	O
mismatch	O
until	O
these	O
values	O
are	O
identical	O
on	O
these	O
routers	B-Protocol
.	O
</s>
<s>
EIGRP	B-Protocol
scales	O
the	O
interface	O
Bandwidth	O
and	O
Delay	O
configuration	O
values	O
with	O
following	O
calculations	O
:	O
</s>
<s>
On	O
Cisco	O
routers	B-Protocol
,	O
the	O
interface	O
bandwidth	O
is	O
a	O
configurable	O
static	O
parameter	O
expressed	O
in	O
kilobits	O
per	O
second	O
(	O
setting	O
this	O
only	O
affects	O
metric	O
calculation	O
and	O
not	O
actual	O
line	O
bandwidth	O
)	O
.	O
</s>
<s>
EIGRP	B-Protocol
takes	O
this	O
value	O
directly	O
without	O
scaling	B-Architecture
into	O
the	O
weighted	O
formula	O
.	O
</s>
<s>
IGRP	B-Protocol
uses	O
the	O
same	O
basic	O
formula	O
for	O
computing	O
the	O
overall	O
metric	O
,	O
the	O
only	O
difference	O
is	O
that	O
in	O
IGRP	B-Protocol
,	O
the	O
formula	O
does	O
not	O
contain	O
the	O
scaling	B-Architecture
factor	O
of	O
256	O
.	O
</s>
<s>
In	O
fact	O
,	O
this	O
scaling	B-Architecture
factor	O
was	O
introduced	O
as	O
a	O
simple	O
means	O
to	O
facilitate	O
backward	O
compatility	O
between	O
EIGRP	B-Protocol
and	O
IGRP	B-Protocol
:	O
In	O
IGRP	B-Protocol
,	O
the	O
overall	O
metric	O
is	O
a	O
24-bit	O
value	O
while	O
EIGRP	B-Protocol
uses	O
a	O
32-bit	O
value	O
to	O
express	O
this	O
metric	O
.	O
</s>
<s>
This	O
way	O
,	O
redistributing	O
information	O
between	O
EIGRP	B-Protocol
and	O
IGRP	B-Protocol
involves	O
simply	O
dividing	O
or	O
multiplying	O
the	O
metric	O
value	O
by	O
a	O
factor	O
of	O
256	O
,	O
which	O
is	O
done	O
automatically	O
.	O
</s>
<s>
A	O
feasible	O
successor	O
for	O
a	O
particular	O
destination	O
is	O
a	O
next	O
hop	O
router	B-Protocol
that	O
is	O
guaranteed	O
not	O
to	O
be	O
a	O
part	O
of	O
a	O
routing	B-Protocol
loop	I-Protocol
.	O
</s>
<s>
However	O
,	O
in	O
most	O
references	O
about	O
EIGRP	B-Protocol
the	O
term	O
feasible	O
successor	O
is	O
used	O
to	O
denote	O
only	O
those	O
routes	O
which	O
provide	O
a	O
loop-free	O
path	O
but	O
which	O
are	O
not	O
successors	O
(	O
i.e.	O
</s>
<s>
At	O
any	O
time	O
,	O
a	O
router	B-Protocol
can	O
send	O
a	O
packet	O
to	O
a	O
destination	O
marked	O
"	O
Passive	O
"	O
through	O
any	O
of	O
its	O
successors	O
or	O
feasible	O
successors	O
without	O
alerting	O
them	O
in	O
the	O
first	O
place	O
,	O
and	O
this	O
packet	O
will	O
be	O
delivered	O
properly	O
.	O
</s>
<s>
Also	O
,	O
when	O
performing	O
unequal-cost	O
load-balancing	O
(	O
balancing	O
the	O
network	O
traffic	O
in	O
inverse	O
proportion	O
to	O
the	O
cost	O
of	O
the	O
routes	O
)	O
,	O
the	O
feasible	O
successors	O
are	O
used	O
as	O
next	O
hops	O
in	O
the	O
routing	B-Protocol
table	I-Protocol
for	O
the	O
load-balanced	B-Application
destination	O
.	O
</s>
<s>
By	O
default	O
,	O
the	O
total	O
count	O
of	O
successors	O
and	O
feasible	O
successors	O
for	O
a	O
destination	O
stored	O
in	O
the	O
routing	B-Protocol
table	I-Protocol
is	O
limited	O
to	O
four	O
.	O
</s>
<s>
A	O
passive	O
state	O
is	O
a	O
state	O
when	O
the	O
router	B-Protocol
has	O
identified	O
the	O
successor(s )	O
for	O
the	O
destination	O
.	O
</s>
<s>
The	O
destination	O
changes	O
back	O
from	O
active	O
to	O
passive	O
when	O
the	O
router	B-Protocol
received	O
replies	O
to	O
all	O
queries	O
it	O
has	O
sent	O
to	O
its	O
neighbors	O
.	O
</s>
<s>
Notice	O
that	O
if	O
a	O
successor	O
stops	O
satisfying	O
the	O
feasibility	O
condition	O
but	O
there	O
is	O
at	O
least	O
one	O
feasible	O
successor	O
available	O
,	O
the	O
router	B-Protocol
will	O
promote	O
a	O
feasible	O
successor	O
with	O
the	O
lowest	O
total	O
distance	O
(	O
the	O
distance	O
as	O
reported	O
by	O
the	O
feasible	O
successor	O
plus	O
the	O
cost	O
of	O
the	O
link	O
to	O
this	O
neighbor	O
)	O
to	O
a	O
new	O
successor	O
and	O
the	O
destination	O
will	O
remain	O
in	O
the	O
passive	O
state	O
.	O
</s>
<s>
The	O
feasibility	O
condition	O
is	O
a	O
sufficient	O
condition	O
for	O
loop	O
freedom	O
in	O
EIGRP-routed	O
network	O
.	O
</s>
<s>
If	O
,	O
for	O
a	O
destination	O
,	O
a	O
neighbor	O
router	B-Protocol
advertises	O
a	O
distance	O
that	O
is	O
strictly	O
lower	O
than	O
our	O
feasible	O
distance	O
,	O
then	O
this	O
neighbor	O
lies	O
on	O
a	O
loop-free	O
route	O
to	O
this	O
destination	O
.	O
</s>
<s>
If	O
,	O
for	O
a	O
destination	O
,	O
a	O
neighbor	O
router	B-Protocol
tells	O
us	O
that	O
it	O
is	O
closer	O
to	O
the	O
destination	O
than	O
we	O
have	O
ever	O
been	O
,	O
then	O
this	O
neighbor	O
lies	O
on	O
a	O
loop-free	O
route	O
to	O
this	O
destination	O
.	O
</s>
<s>
These	O
neighbors	O
will	O
be	O
re-evaluated	O
for	O
possible	O
usage	O
if	O
the	O
router	B-Protocol
transitions	O
to	O
Active	O
state	O
for	O
that	O
destination	O
.	O
</s>
<s>
EIGRP	B-Protocol
features	O
load	B-Application
balancing	I-Application
on	O
paths	O
with	O
different	O
costs	O
.	O
</s>
<s>
A	O
multiplier	O
,	O
called	O
variance	O
,	O
is	O
used	O
to	O
determine	O
which	O
paths	O
to	O
include	O
into	O
load	B-Application
balancing	I-Application
.	O
</s>
<s>
The	O
variance	O
is	O
set	O
to	O
1	O
by	O
default	O
,	O
which	O
means	O
load	B-Application
balancing	I-Application
on	O
equal	O
cost	O
paths	O
.	O
</s>
<s>
Each	O
path	O
with	O
a	O
metric	O
that	O
is	O
smaller	O
than	O
the	O
result	O
is	O
used	O
in	O
load	B-Application
balancing	I-Application
.	O
</s>
<s>
With	O
the	O
functionality	O
of	O
the	O
Unequal	O
Path	O
Cost	O
Load	B-Application
Balancing	I-Application
on	O
EIGRP	B-Protocol
,	O
OSPF	B-Protocol
protocol	O
is	O
unable	O
to	O
design	O
the	O
network	O
by	O
Unequal	O
Path	O
Cost	O
Load	B-Application
Balancing	I-Application
.	O
</s>
<s>
Regarding	O
the	O
Unequal	O
Path	O
Cost	O
Load	B-Application
Balancing	I-Application
function	O
on	O
industry	O
usage	O
,	O
the	O
network	O
design	O
can	O
be	O
flexible	O
with	O
the	O
traffic	O
management	O
.	O
</s>
<s>
Cisco	O
released	O
details	O
of	O
the	O
proprietary	O
EIGRP	B-Protocol
routing	B-Protocol
protocol	I-Protocol
in	O
an	O
RFC	O
in	O
an	O
effort	O
to	O
assist	O
companies	O
whose	O
networks	O
operate	O
in	O
a	O
multi-vendor	O
environment	O
.	O
</s>
<s>
EIGRP	B-Protocol
was	O
developed	O
20	O
years	O
ago	O
,	O
yet	O
it	O
is	O
still	O
one	O
of	O
the	O
primary	O
Cisco	O
routing	B-Protocol
protocols	I-Protocol
due	O
to	O
its	O
purported	O
usability	B-General_Concept
and	O
scalability	B-Architecture
in	O
comparison	O
to	O
other	O
protocols	O
.	O
</s>
<s>
Cisco	O
has	O
stated	O
that	O
EIGRP	B-Protocol
is	O
an	O
open	O
standard	O
but	O
they	O
leave	O
out	O
several	O
core	O
details	O
in	O
the	O
RFC	O
definition	O
which	O
makes	O
interoperability	O
hard	O
to	O
setup	O
between	O
different	O
vendors	O
 '	O
routers	B-Protocol
when	O
the	O
protocol	O
is	O
used	O
.	O
</s>
<s>
Even	O
Cisco	B-Operating_System
NX-OS	I-Operating_System
for	O
example	O
does	O
not	O
support	O
unequal	O
cost	O
load	B-Application
balancing	I-Application
.	O
</s>
<s>
As	O
of	O
2022	O
EIGRP	B-Protocol
has	O
alpha	O
support	O
in	O
FRRouting	B-Protocol
and	O
it	O
seems	O
to	O
be	O
generally	O
unsupported	O
by	O
other	O
routing	B-Application
software	I-Application
.	O
</s>
