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Chapter 14

Routing ProtocolsRIP, OSPF, BGP

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Figure 14-1

Autonomous systems

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Figure 14-2

Popular routing protocols

Distance Vector Link State Path Vector

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Distance Vector Routing.

Forouzan + CCNA:

Slow convergence. Routing loops. Counting to infinity. Split horizon Route poisoning. Triggered update.

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RIP:Routing

InformationProtocol

14.314.3

Exposición equipo 5

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Example of updating a routing

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Initial routing tables in a small autonomous system

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Final routing tables for the previous figure

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RIP message format

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Request messages

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Example 1Example 1

What is the periodic response sent by router R1 in Figure 13.8 (next slide)? Assume R1 knows about the whole autonomous system.

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Example 1

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SolutionSolution

R1 can advertise three networks 144.2.7.0, 144.2.9.0, and 144.2.12.0. The periodic response (update packet) is shown in Figure 13.9 (next slide).

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Solution to Example 1

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RIP timers

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Example 2Example 2

A routing table has 20 entries. It does not receive information about five routes for 200 seconds. How many timers are running at this time?

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SolutionSolution

The timers are listed below:

Periodic timer: 1

Expiration timer: 20 5 15

Garbage collection timer: 5

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Slow convergence

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Hop count

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Instability

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Split horizon

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Poison reverse

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RIP-v2 Format

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RIP version 2 supports RIP version 2 supports CIDR.CIDR.

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Authentication

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RIP uses the services of UDP RIP uses the services of UDP on well-known port 520.on well-known port 520.

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OSPF:OSPF:Open Shortest

Path First

14.514.5

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Areas in an autonomous system

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Types of links

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Point-to-point link

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Transient link

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Stub link

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Example of an internet

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Graphical representation of an internet

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Types of LSAs

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Router link

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Network link

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Summary link to network

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Summary link to AS boundary router

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External link

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Example 3Example 3

In Figure 14.31 (next slide), which router(s) sends out router link LSAs?

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Figure 14-31

Example 3 and Example 4

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SolutionSolution

All routers advertise router link LSAs.

R1 has two links, Net1 and Net2.

R2 has one link, Net2 in this AS.

R3 has two links, Net2 and Net3.

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Example 4Example 4

In Figure 14.31, which router(s) sends out the network link LSAs?

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SolutionSolution

All three network must advertise network links:

Advertisement for Net1 is done by R1 because it is the only router and therefore the designated router.

Advertisement for Net2 can be done by either R1, R2, or R3, depending on which one is chosen as the designated router.

Advertisement for Net3 is done by R3 because it is the only router and therefore the designated router.

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In OSPF, all routers have In OSPF, all routers have the same link state database.the same link state database.

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Shortest path calculationDijkstra algorithm

Start

Stop

Set root to local node and move it to tentative list

Among nodes in tentative list, move the one with the shortest path to permanent list.

Tentative listis empty?

Add each unprocessed neighbor of last moved node to tentative list if not already There. If neighbor is in the tentative listwith larger cumulative cost, replace with

new one.

No

Yes

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Shortest path calculationDijkstra algorithm

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F0

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F

N3 N5

0

59

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F

N3 N5

0

59

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F

D E

N3 N5

0

59

9 9

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F

A

D E

N3 N5

0

59

9 9

17

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F

A

D E

B

N3 N5

N4

0

59

9 9

17 13 11

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F

A

D E

B

N3 N5

N4

0

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9 9

17 13 11

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F

A

D E

B

N3 N5

N4

N1

0

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9 9

17 13

20

11

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F

A

D E

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N3 N5

N4

N1

0

59

9 9

17 13

20

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22

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C

20

F

A

D E

B

N3 N5

N4

N1

59

9 9

17 13

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C

N2

20

22

F

A

D E

B

N3 N5

N4

N1

59

9 9

17 13

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F

A

D E

B

C

N3 N5

N4

N1

N2

0

59

9 9

17 13

20

20

22

11

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Types of OSPF packets

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OSPF packet header

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Hello packet

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Database description packet

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Link state request packet

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Link state update packet

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LSA header

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Router link LSA

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Example 5Example 5

Give the router link LSA sent by router 10.24.7.9 in Figure 14.41.

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Figure 14-41

Example 5

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SolutionSolution

This router has three links: two of type 1 (point-to-point) and one of type 3 (stub network). Figure 14.42 shows the router link LSA.

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Figure 14-42

Solution to Example 5

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Network link advertisement format

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Example 6Example 6

Give the network link LSA in Figure 14.44.

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Figure 14-44

Example 6

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SolutionSolution

The network, for which the network link advertises, has three routers attached. The LSA shows the mask and the router addresses. See Figure 14.45.

Note that only one of the routers, the designated router, advertises the network link.

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Figure 14-45

Solution to Example 6

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Summary link to network LSA

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Summary link to AS boundary LSA

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External link LSA

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Link state acknowledgment packet

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OSPF packets are OSPF packets are encapsulated in IP datagrams.encapsulated in IP datagrams.