Introduction to Dynamic
Routin
g
Protocol
g
Routing Protocols and Concepts – Chapter 3
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Objectives
 D
esc
ri
be
th
e
r
o
l
e

o
f
dy
n
a
mi
c
r
ou


by

routing

protocols

and identify the metric types used by dynamic routing
protocols.
 Determine the administrative distance of a route and
describe its importance in the routing process.
 Identify the different elements of the routing table.
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Dynamic Routing Protocols
 D
y
n
a
mi
c
r
ou
tin
g

p
r

es.
 Typically, a network uses a combination
f b th d i ti t l d
o
f

b
o
th
a
d
ynam
i
c rou
ti
ng pro
t
oco
l
an
d

static routes.
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The Evolution of Dynamic Routing Protocols
 One of the earliest routing protocols was Routing Information Protocol (RIP).
RIP h l d i t i RIP 2 H

di
a
t
e
S
ys
t
em
(IS
-
IS)
.
 Cisco developed Interior Gateway Routing Protocol (IGRP) and Enhanced IGRP
(EIGRP), which also scales well in larger network implementations.

Additionally there was the need to interconnect different internetworks and provide

Additionally
,
there

was

the

need

to

interconnect


IP
,
the

IPv4

addressing

space

is nearly exhausted. Thus IPv6 has emerged. To support the communication based
on IPv6, newer versions of the IP routing protocols have been developed (see the
IPv6 row in the table).
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Dynamic Routing Protocols
 Function(s) of Dynamic Routing Protocols:
-Dynamically share information between routers.
-Automatically update routing table when topology changes.
-
Determine best path to a destination
Determine

best

path


dedicating

part

of

a

router s

resources for protocol operation including CPU time and network link bandwidth.
– One of the primary benefits to using a dynamic routing protocol is that routers
exchange routing information whenever there is a topology change. This exchange
ll t t t ti ll l b t t k d l t fi d lt t
a
ll
ows rou
t
ers
t
o au
t
oma
ti
ca
ll
y
l
earn a
b

e
th
e

be
n
e
fit
s

o
f
dy
n
a
mi
c
r
ou
tin
g,

s
t
a
ti
c
r
ou
tin

More often than not you will find a combination of both
More

often

than

not
,
you

will

find

a

combination

of

both

types of routing in any network that has a moderate level of
complexity.
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Dynamic Routing Protocols

d
a new
b
es
t
pa
th
if

th
e curren
t
pa
th

i
s no
l
onger ava
il
a
bl
e
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Dynamic Routing Protocols
Dynamic


routing

information

and

best

path

determination
–Routing protocol messages
Th f
di i i hb
d
hf
•
Th
ese are messages
f
or
di
scover
i
ng ne
i
g
hb
ors an
d

the

operations

of

a

dynamic

routing

protocol

can

be

described

as

follows:
–The router sends and receives routing messages on its interfaces.
–
The router shares routing messages and routing information with other routers that
are using the same routing protocol.
–Routers exchange routing information to learn about remote networks.
–
When a router detects a topology change the routing protocol can advertise this


administrator

to

understand
-Easy to configure
-
No extra resources are needed
-Protocols automatically react to the
topology changes.
-Confi
g
uration is less erro
r
-prone.
No

extra

resources

are

needed
-More secure
 Disadvantages of static routing
g
-More scalable, growing the network
usually does not present a problem

,

-More administrator knowledge is
required for configuration,
verification, and troubleshooting.
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g
p,
especially in large networks
Dynamic Routing Protocols
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Classifying Routing Protocols
 D
y
namic routin
g

p
rotocols are
g
rou
p
ed accordin
g

•A distance vector interior routing protocol
–
IGRP
•The distance vector interior routing
developed by Cisco (deprecated from 12.2
IOS and later)
–
EIGRP
•The advanced distance vector interior
routing protocol developed by Cisco
OSPF
–
OSPF
•A link-state interior routing protocol
–IS-IS
•A link-state interior routing protocol
–BGP
•
A

p
ath vector exterior routin
g

p
rotocol
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networks within the control of a sin
g
le or
g
anization.
gg
–An autonomous system is commonly comprised of many
individual networks belonging to companies, schools, and
other institutions.
• IGPs for IP include RIP, IGRP, EIGRP, OSPF, and IS-IS
Exterior Gateway Protocols
(EGP)
-
Exterior

Gateway

Protocols
(EGP)
•are used for inter-autonomous system routing - routing
between autonomous systems that are under the control
of different administrations
•
At the ISP level, there are often more important issues
At

the

ISP


networks

under

a

common

administration

sharing a common routing strategy.
To the outside world, an AS is viewed as a single
entity. The AS may be run by one or more
operators while presenting a consistent view of
routing to the external world.
 The American Registry of Internet Numbers
(ARIN), a service provider, or an administrator
assi
g
ns an identif
y
in
g
number to each AS. This
gyg
autonomous system number is a 16 bit number.
Routing protocols, such as Cisco’s IGRP,
require assignment of a unique, autonomous
system number.
American Registry for Internet Numbers

Autonomous systems
Autonomous

systems

 />RFC 1930
 AS just like IP, it needs
to apply from ARIN or
the appropriate region
and be unique on the
it t
i
n
t
erne
t
.
 The Internet Assigned
Numbers Authority
(IANA) has reserved the
following block of AS
numbers for private use
(not to be advertised on
the global Internet):
64512 through 65535
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Classifying Routing Protocols

along the path to the final destination.
•Distance vector routin
g

p
rotocols do not have an
gp
actual map of the network topology
– Generally, periodic updates.
•Some distance vector protocols periodically send
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complete routing tables to all connected neighbors.
Classifying Routing Protocols
Classifying

Routing

Protocols
 IGP: Comparison of Distance Vector &
Link State
Routing Protocols
Link

State
Routing

Protocols


of

the

network.
– updates are not periodic.
•After the network has converged, a link-state
update only sent when there is a change in the
topology.
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Classifying Routing Protocols
Classifying

Routing

Protocols
 Comparison of Distance Vector & Link State Routing Protocols
Di t t t l k

Di
s
t
ance vec
t
or pro
t

protocols.
knowledge

of

the

implemented

link
state routing protocol.
–Fast convergence of the network is
crucial
–Specific types of networks, such
as hub-and-spoke networks, are
being implemented.
crucial
.
–Worst-case convergence times
in a network are not a concern.
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Classifying Routing Protocols
 Classful routing protocols
–
Do NOT send
subnet mask in routing updates
Do

can

only

do

it

once

and

all

network needs to have the identical mask.
–Routing protocols such as RIPv1 and IGRP.
 Classless routin
g

p
rotocols
gp
–Do send subnet mask in routing updates.
–support variable length subnet masks (VLSM).
•In the fi
g
ure
,
the classless version of the network is
g,

ce
i
s

de
fin
ed

as
wh
e
n
a
ll r
ou
t
e
r
s
’ r
ou
tin
g

Co e ge ce
sdeedas eaouesoug
tables are at a state of consistency
– The network has converged when all routers have complete and
f
accurate in

i
r rou
ti
ng
tables.
Rti t l b tdb d

R
ou
ti
ng pro
t
oco
l
s can
b
e ra
t
e
d

b
ase
d
on
the speed to convergence; the faster the
convergence, the better the routing
tl
pro
t

b
e a
bl
e to eva
l
uate an
d

differentiate between the available paths.
For this purpose a metric is used.
 Metric
–A value used by a routing protocol to
determine which routes are better than others.
 Each routing protocol uses its own metric.
–RIP uses hop count,
•
The hop count refers to the number of routers
The

hop

count

refers

to

the

number

OSPF
uses

bandwidth

(cost)
.

Routing Protocols Metrics
 Metrics used in IP routing protocols
–
Bandwidth
•Influences path selection by preferring the path
with the highest bandwidth
–
Cost
Cost
•A value determined either by the IOS or by the
network administrator to indicate preference for a
route. Cost can represent a metric, a combination
of metrics or a
p
olic
y
.
RIP
OSPF
py
–Delay
•Considers the time a packet takes to traverse a


or

previous link failures
Routing Protocols Metrics
Routing

Protocols

Metrics
 The Metric Field in the Routing Table
 Metric used for each routing protocol
-RIP - hop count
-IGRP & EIGRP - Bandwidth (used by
default), Delay (used by default), Load,
Reliability
Reliability
-IS-IS & OSPF – Cost, Bandwidth
(Cisco’s implementation)

Refer to the example in the figure The
Refer

to

the

example

in

the brackets for a routing table entry.
–In the figure, R2 has a route to the
192.168.8.0/24 network that is 2 hops
away.
•
R 192 168 8 0/24 [120/2] via
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R

192
.
168
.
8
.
0/24

[120/2]

via

192.168.4.1, 00:00:26, Serial0/0/1