Chapter 3: OSPF Route Summarization

Chapter 3: OSPF Route Summarization


Objective

This lab focuses on implementing OSPF route summarization techniques to optimize OSPF network performance by reducing the number of LSAs in the topology. By the end of this lab, participants will understand how to summarize routes at the ABR and ASBR levels using Type-3 and Type-5 LSA summarization.


Key Features Implemented

  • LSA Type-3 summarization (inter-area route summarization)
  • LSA Type-5 summarization (external route summarization)
  • Impact of summarization on OSPF database size and convergence

Topology

The lab utilizes the OSPF multi-area topology as shown in the diagram from page 1 of the "Chapter 3: OSPF Route Summarization" PDF.

OSPF Route Summarization Topology Diagram

Configuration Tasks

  • Configuration Tasks:
    • Configure IP addresses and routing protocols as shown in the topology.
    • Assign IP addresses to all interfaces as per the topology.
    • Configure OSPF on the router interfaces in the appropriate areas.
  • Implement Route Summarization at ABRs:
    • Configure R2 ABR to advertise only a summarized view of the loopback networks (of R4, Area 1) into Area 0.
    • Configure R3 ABR to advertise only a summarized view of the loopback networks (of R5, Area 2) into Area 0.
  • Implement Route Summarization at ASBRs:
    • Redistribute the loopback interfaces of R1 into OSPF so they appear as external routes in the OSPF domain.
    • Configure OSPF to redistribute only a single summary for all the external loopback networks, using the most optimal summary.
  • Verify the impact of summarization:
    • Ensure that summarized routes appear in the routing tables of routers.
    • Check that unnecessary specific routes are not advertised.

Base Configurations

Ready to get started? Here, you'll find the initial configurations for each device to begin this lab.
hostname R1

interface Loopback0
 ip address 10.1.0.1 255.255.255.0
interface Loopback1
 ip address 10.1.1.1 255.255.255.0
interface Loopback2
 ip address 10.1.10.1 255.255.255.0
interface Loopback3
 ip address 10.1.15.1 255.255.255.0
interface Ethernet0/0
 ip address 12.1.1.1 255.255.255.252
 ip ospf 1 area 0
interface Ethernet0/1
 ip address 13.1.1.1 255.255.255.252
 ip ospf 1 area 0

router ospf 1
 redistribute connected subnets
hostname R2

interface Ethernet0/0
 ip address 12.1.1.2 255.255.255.252
 ip ospf 2 area 0
interface Ethernet0/1
 ip address 24.1.1.1 255.255.255.252
 ip ospf 2 area 1

router ospf 2
hostname R3

interface Ethernet0/0
 ip address 13.1.1.2 255.255.255.252
 ip ospf 3 area 0
interface Ethernet0/1
 ip address 35.1.1.1 255.255.255.252
 ip ospf 3 area 2

router ospf 3
hostname R4

interface Loopback0
 ip address 192.168.0.1 255.255.255.255
 ip ospf 4 area 1
interface Loopback1
 ip address 192.168.1.1 255.255.255.255
 ip ospf 4 area 1
interface Loopback2
 ip address 192.168.2.1 255.255.255.255
 ip ospf 4 area 1
interface Loopback3
 ip address 192.168.3.1 255.255.255.255
 ip ospf 4 area 1
interface Ethernet0/0
 ip address 24.1.1.2 255.255.255.252
 ip ospf 4 area 1

router ospf 4
hostname R5

interface Loopback0
 ip address 172.16.1.1 255.255.255.255
 ip ospf 5 area 2
interface Loopback1
 ip address 172.16.2.1 255.255.255.255
 ip ospf 5 area 2
interface Loopback2
 ip address 172.16.3.1 255.255.255.255
 ip ospf 5 area 2
interface Loopback3
 ip address 172.16.4.1 255.255.255.255
 ip ospf 5 area 2
interface Loopback4
 ip address 172.16.5.1 255.255.255.255
 ip ospf 5 area 2
interface Loopback5
 ip address 172.16.6.1 255.255.255.255
 ip ospf 5 area 2
interface Loopback6
 ip address 172.16.7.1 255.255.255.255
 ip ospf 5 area 2
interface Ethernet0/0
 ip address 35.1.1.2 255.255.255.252
 ip ospf 5 area 2

router ospf 5

Verification Commands

  • show ip ospf
    • Verify general OSPF process details, including summarization settings.
  • show ip ospf interface
    • Confirm which interfaces are participating in OSPF.
  • show ip ospf neighbor
    • Check adjacency states.
  • show ip ospf database
    • Verify LSA Type-3 and Type-5 summary LSAs.
  • show ip route ospf
    • Confirm that summarized routes are installed in the routing table.

Expected Outcomes

  • The routing table should display only summarized routes instead of multiple individual subnets.
  • Type-3 and Type-5 LSAs for the loopback networks should reflect summarized routes instead of individual networks.
  • OSPF database size should be reduced, leading to improved network efficiency.

Final Configurations

Want to take a look for yourself? Here, you will find the final configurations of each device required for this lab.
hostname R1

interface Loopback0
 ip address 10.1.0.1 255.255.255.0
interface Loopback1
 ip address 10.1.1.1 255.255.255.0
interface Loopback2
 ip address 10.1.10.1 255.255.255.0
interface Loopback3
 ip address 10.1.15.1 255.255.255.0
interface Ethernet0/0
 ip address 12.1.1.1 255.255.255.252
 ip ospf 1 area 0
interface Ethernet0/1
 ip address 13.1.1.1 255.255.255.252
 ip ospf 1 area 0

router ospf 1
 summary-address 10.1.0.0 255.255.240.0
 redistribute connected subnets
hostname R2

interface Ethernet0/0
 ip address 12.1.1.2 255.255.255.252
 ip ospf 2 area 0
interface Ethernet0/1
 ip address 24.1.1.1 255.255.255.252
 ip ospf 2 area 1

router ospf 2
 area 1 range 192.168.0.0 255.255.252.0
hostname R3

interface Ethernet0/0
 ip address 13.1.1.2 255.255.255.252
 ip ospf 3 area 0
interface Ethernet0/1
 ip address 35.1.1.1 255.255.255.252
 ip ospf 3 area 2

router ospf 3
 area 2 range 172.16.0.0 255.255.248.0
hostname R4

interface Loopback0
 ip address 192.168.0.1 255.255.255.255
 ip ospf 4 area 1
interface Loopback1
 ip address 192.168.1.1 255.255.255.255
 ip ospf 4 area 1
interface Loopback2
 ip address 192.168.2.1 255.255.255.255
 ip ospf 4 area 1
interface Loopback3
 ip address 192.168.3.1 255.255.255.255
 ip ospf 4 area 1
interface Ethernet0/0
 ip address 24.1.1.2 255.255.255.252
 ip ospf 4 area 1

router ospf 4
hostname R5

interface Loopback0
 ip address 172.16.1.1 255.255.255.255
 ip ospf 5 area 2
interface Loopback1
 ip address 172.16.2.1 255.255.255.255
 ip ospf 5 area 2
interface Loopback2
 ip address 172.16.3.1 255.255.255.255
 ip ospf 5 area 2
interface Loopback3
 ip address 172.16.4.1 255.255.255.255
 ip ospf 5 area 2
interface Loopback4
 ip address 172.16.5.1 255.255.255.255
 ip ospf 5 area 2
interface Loopback5
 ip address 172.16.6.1 255.255.255.255
 ip ospf 5 area 2
interface Loopback6
 ip address 172.16.7.1 255.255.255.255
 ip ospf 5 area 2
interface Ethernet0/0
 ip address 35.1.1.2 255.255.255.252
 ip ospf 5 area 2

router ospf 5
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