© Copyright Lenovo 2018
Chapter 28: OSPF
397
Interface Cost
The
OSPF
link
‐
state
algorithm
(Dijkstra’s
algorithm)
places
each
routing
device
at
the
root
of
a
tree
and
determines
the
cumulative
cost
required
to
reach
each
destination.
Usually,
the
cost
is
inversely
proportional
to
the
bandwidth
of
the
interface.
Low
cost
indicates
high
bandwidth.
You
can
manually
enter
the
cost
for
the
output
route
with
the
following
command:
Electing the Designated Router and Backup
In
any
area
with
more
than
two
routing
devices,
a
Designated
Router
(DR)
is
elected
as
the
central
contact
for
database
exchanges
among
neighbors,
and
a
Backup
Designated
Router
(BDR)
is
elected
in
case
the
DR
fails.
DR
and
BDR
elections
are
made
through
the
hello
process.
The
election
can
be
influenced
by
assigning
a
priority
value
to
the
OSPF
interfaces
on
the
NE2552E.
The
command
is
as
follows:
A
priority
value
of
255
is
the
highest,
and
1
is
the
lowest.
A
priority
value
of
0
specifies
that
the
interface
cannot
be
used
as
a
DR
or
BDR.
In
case
of
a
tie,
the
routing
device
with
the
highest
router
ID
wins.
Interfaces
configured
as
passive
do
not
participate
in
the
DR
or
BDR
election
process:
Summarizing Routes
Route
summarization
condenses
routing
information.
Without
summarization,
each
routing
device
in
an
OSPF
network
would
retain
a
route
to
every
subnet
in
the
network.
With
summarization,
routing
devices
can
reduce
some
sets
of
routes
to
a
single
advertisement,
reducing
both
the
load
on
the
routing
device
and
the
perceived
complexity
of
the
network.
The
importance
of
route
summarization
increases
with
network
size.
Summary
routes
can
be
defined
for
up
to
16
IP
address
ranges
using
the
following
command:
where
<range
number>
is
a
number
1
to
16,
<IPv4
address>
is
the
base
IP
address
for
the
range,
and
<subnet
mask>
is
the
IPv4
address
mask
for
the
range.
For
a
detailed
configuration
example,
see
.
Note:
OSPFv2
supports
IPv4
only.
IPv6
is
supported
in
OSPFv3
(see
).
NE2552E(config-ip-if)#
ip ospf cost
<cost
value
(1
‐
65535)>
NE2552E(config-ip-if)#
ip ospf priority
<priority
value
(0
‐
255)>
NE2552E(config-ip-if)#
ip ospf passive-interface
NE2552E(config-ip-if)#
exit
NE2552E(config)#
router ospf
NE2552E(config-router-ospf)#
area-range
<range
number>
address
<IP address>
<mask>
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