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Chapter 3

Dynamic Routing Protocols

CIS 82 Routing Protocols and Concepts

Rick GrazianiCabrillo College

[email protected]

Spring 2010



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Note

My web site is www.cabrillo.edu/~rgraziani.

For access to these PowerPoint presentations and othermaterials, please email me at [email protected].



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For further information

This presentation is an

overview of what iscovered in thecurriculum/book.

For further explanationand details, please readthe chapter/curriculum.

Book:

Routing Protocolsand Concepts

By Rick Graziani and Allan Johnson

ISBN: 1-58713-206-0

ISBN-13: 978-58713-206-3



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Topics

Introduction to Dynamic Routing

Protocols Perspective and Background

Network Discovery and

Routing Table Maintenance

Dynamic Routing Protocol

Advantages Classifying Dynamic Routing

Protocols

IGP and EGP

Distance Vector and Link-

State

Classful and Classless

Convergence

Metrics

Purpose of the Metric

Metrics and Routing Protocols

Load Balancing

Administrative Distance

Purpose of AdministrativeDistance

Dynamic Routing Protocolsand Administrative Distance

Static Routes and Administrative Distance

Directly Connected Networksand Administrative Distance



Introduction to Dynamic Routing

Protocols Perspective and Background

Network Discovery and Routing Table Maintenance

Dynamic Routing Protocol Advantages



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Perspective and Background

Dynamic routing protocols have evolved over several years

As networks have evolved and become more complex, new routing

protocols have emerged.

Most institutions have migrated to new protocols, others are still in use.



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Perspective and

Background

Interior Routing Protocols or Interior Gateway Protocols (IGP)

Distance Vector

RIPv1 – Simple, Classful, limited metrics (hop count)

RIPv2 – Simple, Classless, limited metrics (hop count)

Cisco Proprietary IGRP – Simple, Classful, better metric (BW, delay, reliab., load)

EIGRP – Simple, Classless, same metric, DUAL (backup routes)

Link State

OSPF – Perceived complex, classless, Cisco metric BW, IETF

IS-IS - Perceived complex, classless, metric ―default‖, ISO

Classful (does not support

CIDR and VLSM)

Classless (supports CIDR

and VSLM)



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Perspective and

Background

Exterior Routing Protocols or Exterior Gateway Protocols (EGP)

Border Gateway Protocol (BGP)

Between ISPs (Internet service providers)

Between ISPs and their larger private clients

Path Vector routing protocol, metric – attributes (policies)

Replaced EGP



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Role of Dynamic Routing Protocol

Dynamic Routing Protocols:

Exchange of routing information between routers

Dynamically learn information about remote networks Determines the best path to each network

Automatically learn about new networks

Automatically finds alternate paths if needed (link failure in current path)

Update

Update

UpdateUpdate

Update

Update



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What is an advantage of dynamic routing protocols compared to

static routes?

Less administrative overhead (change modifications)

More work and more chances to make a mistake.

Make additions, deletions, and

modifications to static routes!

Add new static routes…

Static Routes



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Change in network using a dynamic routing protocol.

Dynamic routing protocols automatically adjust to changes in the network:

New networks

Deleted networks

Changes in topology

Configuration is less error-prone

Scales better with larger networks

No changes!

Add dynamic routing

protocol…

Dynamic Routing Protocol



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Disadvantages of using Dynamic routing protocol

More CPU and memory requirements (not usually a problem)

This is not that big an issue in most networks and withmodern routers.

―Less secure‖ if routing updates are sent unencrypted.

Most networks use both dynamic and static routes



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Purpose of Dynamic Routing Protocols

A routing protocol is a set of processes, algorithms, and messages thatare used to exchange routing information and populate the routing tablewith the routing protocol’s choice of best paths.

Components of a routing protocol (depending upon the routing protocol):

Data structures: Tables or databases for their operations, kept in RAM.

Algorithm:

Routing protocols use algorithms for processing routing informationand for best-path determination.

Routing protocol messages:

Discover neighboring routers

Exchange routing information

Learn and maintain accurate information about the network

I’m R1 I’m R3

My routesMy routes

ChangesChanges



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Dynamic Routing Protocol Operation

The operations of a dynamic routing protocol vary depending on the type ofrouting protocol, but in general:

1. The router shares routing messages and routing information with otherrouters that are using the same routing protocol.

2. The router sends and receives routing messages on its interfaces.

3. Routers exchange routing information to learn about remote networks.

4. When a router detects a topology change, the routing protocol can advertisethis change to other routers.

Update

Update

UpdateUpdate

Update

Update

I’m running RIP and

will share with other

routers running RIP.

I’m running RIP too.

I’m running RIP too.

I just learned

about remote

networks

from R2 and

R3.

I just learned about

remote networks from

R1 and R3.

I just learned about

remote networks from

R1 and R2.

X

I no longer have a

connection to

this network!

Got it, I will tellR3…

Got it!



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Static Routing

Usage,

Advantages, andDisadvantages

When would you use a static route?

With smaller networks that are not expected to grow significantly.

Routing to and from stub networks

Default route



Classifying Dynamic Routing

Protocols IGP and EGP

Distance Vector and Link-State

Classful and Classless

Convergence



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Classifying Routing Protocols

Routing Protocols can be classified by:

IGP or EGP

Distance vector or link-state

Classful or classless



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IGP and EGP

An autonomous sys tem (AS)—otherwise known as a rout ing dom ain —isa collection of routers under a common administration.

Company’s internal network

An ISP’s network.

Because the Internet is based on the autonomous system concept, twotypes of routing protocols are required:

Interior routing protocols: Within Cabrillo College & within CENIC

Routing inside an autonomous system

Exterior routing protocols: Between ISPs, CENIC and PAIX

Routing between autonomous systems

PAIX

Palo AltoCENIC BGP

Cabrillo

College



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Distance Vector and Link-State Routing Protocols

Interior gateway protocols (IGP) can be classified as two types:

Distance vector routing protocols

Link-state routing protocols



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Distance Vector Routing

Protocol Operation

What does a street sign like this tellyou?

How far (distance)

Which way (direction)

Distance vecto r

Routes are advertised as vectors

of distance and direction.

Distance is defined in terms of a

metric

Such as hop count

Direction is simply the:

Nexthop router or

Exit interface

Typically use the Bellman-Ford

algorithm for the best-path (shortest)route determination



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Protocol Operation

Routing protocol

Does not know the topology of an

internetwork.

Only knows the routing information

received from its neighbors.

Does not know if another path

would actually be faster.

I don’t have a map

of the network.

All I know is how far

and which direction

(to next hop router)

Distance Vector routing protocols are like signposts along the path to the final destination.

Would another path

that is longeractually be faster?

(speed limit)



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Protocol Operation

Where might you use a distancevector routing protocol?

Simple and flat network

The administrators do not have

enough knowledge about link-state

protocols.

Specific types of networks, such as

hub-and-spoke networks, are

being implemented.

Worst-case convergence times ina network are not a concern.

More in Chapter 4.



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Link-State Protocol Operation

Link-state routing protocol can

create a ―complete view,‖ ortopology, of the network.

Link-state protocols are

associated with Shortest Path

First (SPF) calculations.

A l ink -state rou ter uses the link-state information to:

Create a topology map

Select the best path to all

destination networks in the

topology.

Each router makes the

decision!

Link State routing protocols is like having a complete map of the network topology

OR



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Link-State Protocol Operation

Link-state protocols work best

in situations where

The network design is

hierarchical, usually occurring

in large networks.

The administrators have a

good knowledge of theimplemented link-state routing

protocol.

Fast convergence of the

network is crucial.

More in later chapters.



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Classful and Classless Routing Protocols

All routing protocols can also be classified as either

Classful routing protocols

Classless routing protocols

IPv6 routing protocols are classless



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Classful

Routing

Protocols

Classful routing protocols do NOT send subnet mask informationin routing updates.

The first routing protocols, such as RIP

When network addresses were allocated based on classes.

Class A, B, or C.

Network mask determined based on value of first octet of thenetwork address.

172.16.0.0

192.168.1.0

192.168.2.0

172.16.0.0

192.168.1.0

192.168.2.0



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Classful Routing Protocols

Classful routing protocols do not include the subnet mask

Therefore do not support VLSM and CIDR.

All subnets within the same “major classful network address” must have

the same mask.

More later!

172.16.0.0/16

Major Classful

Network



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Classless routing Protocols

Today’s networks are no longer allocated based on classes

Subnet mask cannot be determined by the value of the firstoctet .

Classless routing protocols include the subnet mask with the

network address in routing updates.

172.16.0.0/28

192.168.1.0/24

192.168.2.0/30

172.16.1.0/28

192.168.1.0/24

192.168.2.4/30



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Classless routing Protocols

Classless routing protocols are required in most networks today

because of their support for:

VLSM

CIDR

Discontiguous networks.

172.16.128.0/30 172.16.132.0/30

172.16.136.0/30

172.16.0.0/16

Major Classful

Network

/27 and /30

subnets

Dynamic Routing Protocols and Convergence



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Convergence is when the routing tables of all routers are at a state of

consistency.

Network has converged: When all routers have complete and

accurate information about the network.

Convergence time is the time it takes routers to:

Share information

Calculate best paths

Update their routing tables

A network is not completely operable until the network has converged;

therefore, most networks require short convergence times.


XI no longer have a

connection to

this network!

Got it, I will tell

R3…

Got it!



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Generally, convergence time:

Slow: RIP and IGRP

Faster: EIGRP, OSPF, and IS-IS

R2’s Routing

Table

R1’s Routing

TableR3’s Routing

Table



Metrics

Purpose of the Metric

Metrics and Routing Protocols

Load Balancing



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Purpose of a Metric

Metrics are a way to measure or compare. Determine the best path.

Routing protocol learns multiple routes to the same destination.

Metric is used to determine which path is most preferable

?



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Purpose of a Metric

What might be some ways (metrics) that routing protocols might use todetermine the ―best path?

Routing protocol metrics:

RIP: Hop count IGRP and EIGRP: Bandwidth, delay, reliability and load

OSPF (Cisco’s version): Bandwidth

IS-IS: Four values (Cisco uses ―default‖) – Covered in CCNP

BGP: Attributes – Covered in CCNP

More later



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Metric

Parameters

R1 to reach the 172.16.1.0/24 network.

RIP: Fewest number of hops via R2.

OSPF: Path with the highest cumulative bandwidth through R3.

This results in faster packet delivery.

56 Kbps



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Metric Field in the Routing Table

The routing table displays the metric for each dynamic and staticroute.

Static routes always have a metric of 0.

Routing protocols install route in routing table with the lowest metric.

R2# show ip route

172.16.0.0/24 is subnetted, 3 subnets

C 172.16.1.0 is directly connected, FastEthernet0/0

C 172.16.2.0 is directly connected, Serial0/0/0

C 192.168.1.0/24 is directly connected, Serial0/0/1

S 192.168.2.0/24 [1/0] via 192.168.1.1R 192.168.7.0/24 [120/1] via 192.168.4.1, Serial0/0/1

R 192.168.8.0/24 [120/2] via 192.168.4.1, Serial0/0/1



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All routers running RIP

What is the metric

(distance) for R2 to reachthe 192.168.8.0 network?

2 (hops away)

What is the direction(vector) for R2 to reach the192.168.8.0 network?

Serial 0/0/1 (via R3)

R2# show ip route

<output omitted>

Gateway of last resort is not set

R 192.168.1.0/24 [120/1] via 192.168.2.1, 00:00:24, Serial0/0/0

C 192.168.2.0/24 is directly connected, Serial0/0/0C 192.168.3.0/24 is directly connected, FastEthernet0/0

C 192.168.4.0/24 is directly connected, Serial0/0/1

R 192.168.5.0/24 [120/1] via 192.168.4.1, 00:00:26, Serial0/0/1

R 192.168.6.0/24 [120/1] via 192.168.2.1, 00:00:24, Serial0/0/0

[120/1] via 192.168.4.1, 00:00:26, Serial0/0/1

R 192.168.7.0/24 [120/1] via 192.168.4.1, 00:00:26, Serial0/0/1R 192.168.8.0/24 [120/2] via 192.168.4.1, 00:00:26, Serial0/0/1



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What happens when two or more routes to the same destination have

identical metric values?

The router load balances between these equal-cost paths.

All routing protocols do equal cost load balancing.

EIGRP also does unequal cost load balancing.

Load

Balancing

R2# show ip route

<output omitted>

R 192.168.6.0/24 [120/1] via 192.168.2.1, 00:00:24, Serial0/0/0

[120/1] via 192.168.4.1, 00:00:26, Serial0/0/1



Administrative Distance

Purpose of Administrative Distance

Dynamic Routing Protocols and Administrative

Distance

Static Routes and Administrative Distance Directly Connected Networks and Administrative

Distance



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What if a router learns about a remote

network from two different routingsources.

What if RIP advertises the network as

10 hops away but OSPF advertises it

as a cumulative bandwidth of 100,000.

Which is better RIP or OSPF?

Can’t tell

Can’t compare apples and oranges.

Note: This is not common.

Adm inistrat ive distance (AD) is:

Used to determine which routing

source takes precedence.

Used when there are multiple

routing sources for the same

destination network address.

Lower the AD the more preferred the

routing source.

RIP: 1.1.1.1.

is 10 hops

OSPF: 1.1.1.1.

is 100,000 BW

?

So, which one would

be preferred RIP or

OSPF? OSPF

Which route would be

preferred, OSPF or a Static

Route to the same

network? Static Route



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Cisco uses Administrative distance

(AD) to define the preference of arouting source.

Routing sources:

Directly connected networks

Static routes

Specific routing protocols

AD for static and dynamic can bemodifed (in CCNP)

Note

The term t rustwor th iness iscommonly used when definingadministrative distance.

The lower the administrative distancevalue, the more trustworthy the route.



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AD: 0 to 255.

The lower the value, the morepreferred the route source.

AD of 0 is the most preferred.

Only a directly connectednetwork has an administrative

distance of 0, which cannot bechanged.

No better route to a networkthan being directly connectedto that network.

AD of 255 means the router willnot believe the source of that route

Route will not be installed inthe routing table.



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Verifying AD: show ip route

R2# show ip route

D 192.168.6.0/24 [90/2172416] via 192.168.2.1, 00:00:24, Serial0/0/0

What is the AD of this route? 90



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Verifying AD: show ip protocols

R2# show ip protocols

Routing Protocol is “eigrp 100 “ Outgoing update filter list for all interfaces is not set

Incoming update filter list for all interfaces is not set

Default networks flagged in outgoing updates

Default networks accepted from incoming updates

EIGRP metric weight K1=1, K2=0, K3=1, K4=0, K5=0

EIGRP maximum hopcount 100

EIGRP maximum metric variance 1Redistributing: eigrp 100

Automatic network summarization is in effect

Automatic address summarization:

Maximum path: 4

Routing for Networks:

192.168.2.0

192.168.3.0

192.168.4.0

Routing Information Sources:

Gateway Distance Last Update

192.168.2.1 90 2366569

Distance: internal 90 external 170

<continued next slide?



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show ip protocols (continued)

R2# show ip protocols

Routing Protocol is “rip”

Sending updates every 30 seconds, next due in 12 secondsInvalid after 180 seconds, hold down 180, flushed after 240

Outgoing update filter list for all interfaces is not set

Incoming update filter list for all interfaces is not set

Redistributing: rip

Default version control: send version 1, receive any version

Interface Send Recv Triggered RIP Key-chain

Serial0/0/1 1 2 1FastEthernet0/0 1 2 1

Automatic network summarization is in effect

Maximum path: 4

Routing for Networks:

192.168.3.0

192.168.4.0

Passive Interface(s):

Routing Information Sources:Gateway Distance Last Update

192.168.4.1 120

Distance: (default is 120)

More on show ip protocols later



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Static routes

Default AD = 1 After directly connected networks (AD = 0), static routes are the

most preferred route source.



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R2# show ip route




S 172.16.3.0 is directly connected, Serial0/0/0C 192.168.1.0/24 is directly connected, Serial0/0/1

S 192.168.2.0/24 [1/0] via 192.168.1.1

What is the AD of a Static Route? Static route: default AD = 1 (never 0)

Exit-interface: AD = 1

Next-hop IP address: AD = 1

After directly connected networks (AD = 0), static routes are themost preferred route source.

Exit Interface: ip route 172.16.3.0 255.255.255.0 serial 0/0/0

Next-hop: ip route 192.168.2.0 255.255.255.0 192.168.1.1



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R2# show ip route




S 172.16.3.0 is directly connected, Serial0/0/0C 192.168.1.0/24 is directly connected, Serial0/0/1

S 192.168.2.0/24 [1/0] via 192.168.1.1

The static route to 172.16.3.0 is listed as ―directly connected‖.

It is common misconception to assume that the AD value of this routemust be 0 because it states “directly connected a” - false assumption.




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R2# show ip route 172.16.3.0

Routing entry for 172.16.3.0/24

Known via “static”, distance 1, metric 0 (connected)

Routing Descriptor Blocks:

* directly connected, via Serial0/0/0Route metric is 0, traffic share count is 1

View AD value this static route with an exit-interface, use command show iproute [route] option.




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Directly Connected Networks and Administrative Distance

To see the AD value of a directly connected network, use the commandshow ip route [route] option.

R2# show ip route 172.16.3.0

Routing entry for 172.16.1.0/24Known via “connected”, distance 0, metric 0

(connected, via interface)

Routing Descriptor Blocks:

* directly connected, via FastEthernet0/0

Route metric is 0, traffic share count is 1



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Floating Static

Route (Extra)

There are situations when an administrator will configure a static route to

the same destination that is learned using a dynamic routing protocol, but

using a different path.

The static route will be configured with an AD greater than that of the

routing protocol.

If there is a link failure in the path used by the dynamic routing protocol, the

route entered by the routing protocol is removed from the routing table.

The static route will then become the only source and will automatically be

added to the routing table.

This is known as a f loat ing stat ic rou te and is discussed in CCNP courses.

R2: ip route 192.168.8.0 255.255.255.0 192.168.2.1 5

R2: ip route 192.168.8.0 255.255.255.0 192.168.4.1

X



Chapter 3

Dynamic Routing Protocols

CIS 82 Routing Protocols and Concepts

Rick Graziani

Cabrillo College

[email protected]

cis82-e2-3-dynamicroutingprotocols

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