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CCNP Routing Studies: Basic Open Shortest Path First

  • Sample Chapter is provided courtesy of Cisco Press.
  • Date: May 24, 2002.

Contents

  1. Basic OSPF
  2. Configuring OSPF in a Single Area
  3. OSPF and Nonbroadcast Multiaccess Environments
  4. Scenarios
  5. Practical Exercise: Routing OSPF
  6. Review Questions
  7. Summary

Chapter Description

Understanding basic Open Shortest Path First (OSPF) routing principles not only applies to the CCNP certification but to all Cisco-based certifications. A concrete understanding of how OSPF routing works is fundamental for any small or large network. This chapter focuses on a number of objectives falling under the CCNP routing principles.

From the Book

CCNP Practical Studies: Routing

CCNP Practical Studies: Routing

$54.95

Practical Exercise: Routing OSPF

NOTE

Practical Exercises are designed to test your knowledge of the topics covered in this chapter. The Practical Exercise begins by giving you some information about a situation and then asks you to work through the solution on your own. The solution can be found at the end.

Configure the network in Figure 3-6 for OSPF routing using the IP addressing scheme provided. Ensure that both routers R1 and R2 have full connectivity to Routers R3 and R6 in the backbone. Use the ping command to ensure all networks are reachable. You must use OSPF as your only dynamic routing protocol.

Figure 3-6Figure 3-6 Practical Exercise: Routing OSPF

Practical Exercise Solution

You will notice that the IP addressing scheme uses VLSM and the serial links use the subnet 141.108.10.0.

The serial link contains a mask that is 255.255.255.252, or /30.

The following example configurations provide a solution using OSPF. This practical example is similar to Scenario 2-2 with the extra link between area 1 and area 0. This means that you need to configure two virtual links: one from router R2 to R6 and another between R1 and R3. This second virtual link is required in case of link failure or hardware failure from the Routers R1 and R2.

Configure the loopbacks with VLSM and experiment with debug commands to discover why IP entries are added or not advertised. Remove the second virtual link from R1 to R3, and see how OSPF behaves when the link between R2 and R6 fails.

You will find that because the areas are partitioned, you actually do need two virtual links to ensure full connectivity in any network failure situation. Example 3-62 displays R1's full working configuration.

Example 3-62 R1's Full Configuration

version 12.0

!

hostname R1

!

enable password cisco

!

ip subnet-zero

no ip domain-lookup

interface Loopback0

ip address 131.108.4.1 255.255.255.128

ip ospf cost 90

!

interface Loopback1

ip address 131.108.4.129 255.255.255.128

ip ospf cost 90

!

interface Loopback2

ip address 131.108.5.1 255.255.255.224

ip ospf cost 90

!

interface Ethernet0/0

ip address 131.108.1.1 255.255.255.0

!

interface Serial0/0

ip address 141.108.10.9 255.255.255.252

clockrate 125000

!

interface Serial0/1

no ip address

shutdown

clockrate 128000

!

router ospf 1

area 2 virtual-link 141.108.2.1

network 131.108.1.0 0.0.0.255 area 1

network 131.108.4.0 0.0.0.127 area 1

network 131.108.4.128 0.0.0.127 area 1

network 131.108.5.0 0.0.0.31 area 1

network 141.108.10.8 0.0.0.3 area 2

!

line con 0

line aux 0

line vty 0 4

!

end

Example 3-63 displays R2's full working configuration.

Example 3-63 R2's Full Configuration

version 12.0

service timestamps debug uptime

service timestamps log uptime

no service password-encryption

!

hostname R2

!

enable password cisco

!

ip subnet-zero

no ip domain-lookup

!

interface Loopback0

ip address 131.108.5.33 255.255.255.224

ip ospf network point-to-point

ip ospf cost 1000

!

interface Loopback1

ip address 131.108.6.1 255.255.255.255

!

interface Loopback2

ip address 131.108.6.2 255.255.255.255

!

interface Ethernet0/0

ip address 131.108.1.2 255.255.255.0

ip ospf priority 255

interface Serial1/0

ip address 141.108.10.1 255.255.255.252

!

interface Serial1/1

no ip address

shutdown

!

interface Serial1/2

no ip address

shutdown

!

interface Serial1/3

no ip address

shutdown

!

router ospf 2

area 2 virtual-link 141.108.12.1

network 131.108.1.0 0.0.0.255 area 1

network 131.108.5.32 0.0.0.31 area 1

network 131.108.6.1 0.0.0.0 area 1

network 131.108.6.2 0.0.0.0 area 1

network 141.108.10.0 0.0.0.3 area 2

!

line con 0

line aux 0

line vty 0 4

!

end

Example 3-64 displays R3's working configuration.

Example 3-64 R3's Full Configuration

version 12.0

hostname R3

!

enable password cisco

!

ip subnet-zero

interface Loopback0

ip address 141.108.1.1 255.255.255.128

ip ospf network point-to-point

!

interface Loopback1

ip address 141.108.1.129 255.255.255.128

ip ospf network point-to-point

!

interface Loopback2

ip address 141.108.2.1 255.255.255.224

ip ospf network point-to-point

!

interface Ethernet0

ip address 131.108.33.1 255.255.255.0

!

interface Serial0

ip address 141.108.10.10 255.255.255.252

!

interface Serial1

ip address 141.108.10.5 255.255.255.252

!

router ospf 3

area 2 virtual-link 131.108.5.1

network 131.108.33.0 0.0.0.255 area 0

network 141.108.1.0 0.0.0.127 area 0

network 141.108.1.128 0.0.0.127 area 0

network 141.108.2.0 0.0.0.31 area 0

network 141.108.10.4 0.0.0.3 area 0

network 141.108.10.8 0.0.0.3 area 2

!

line con 0

line aux 0

line vty 0 4

!

end

Finally, Example 3-65 displays R6's working configuration.

Example 3-65 R6's Full Configuration

version 12.0

hostname r6

!

enable password cisco

ip subnet-zero

!

interface Loopback0

ip address 141.108.9.1 255.255.255.128

ip ospf network point-to-point

interface Loopback1

ip address 141.108.9.129 255.255.255.128

ip ospf network point-to-point

interface Loopback2

ip address 141.108.12.1 255.255.255.0

ip ospf network point-to-point

interface Ethernet0

ip address 131.108.26.1 255.255.255.0

media-type 10BaseT

!

interface Serial0

ip address 141.108.10.6 255.255.255.252

clockrate 125000

!

interface Serial1

ip address 141.108.10.2 255.255.255.252

clockrate 125000

!

interface Serial2

shutdown

!

interface Serial3

shutdown

!

router ospf 6

area 2 virtual-link 131.108.6.2

network 131.108.26.0 0.0.0.255 area 0

network 141.108.9.0 0.0.0.127 area 0

network 141.108.9.128 0.0.0.127 area 0

network 141.108.10.0 0.0.0.3 area 2

network 141.108.10.4 0.0.0.3 area 0

network 141.108.12.0 0.0.0.255 area 0

!

line con 0

line aux 0

line vty 0 4

end

6. Review Questions | Next Section Previous Section

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