Chapter 1: Basic OSPF Configuration with Redistribution

Chapter-1: Basic OSPF Configuration with Redistribution


Objective

This lab focuses on configuring OSPF across multiple areas with additional redistribution scenarios to generate Type-4 and Type-5 LSAs. By the end of this lab, participants will understand OSPF redistribution, inter-area communication, and external route advertisement.


Key Features Implemented

  • Multi-Area OSPF configuration
  • OSPF Router ID assignment
  • OSPF DR/BDR elections
  • OSPF Passive interfaces
  • MTU adjustments on OSPF interfaces
  • Route redistribution into OSPF

Topology

The lab uses a multi-area OSPF topology with redistribution from EIGRP AS 10, as depicted in the diagram below.

OSPF Multi-Area Topology with Redistribution Diagram

Configuration Tasks

  1. Assign IP addresses as specified in the topology.
  2. Configure OSPF on all routers using the same Process ID (1).
  3. Set the Router ID (RID) based on the Loopback0 interface of the routers.
  4. Modify DR/BDR election settings for 12.1.1.0/24 network:
    • R4 should not participate in DR/BDR election.
    • R2 should become the DR.
  5. Enable OSPF on interfaces without using the network command.
  6. Ensure that loopback interfaces are advertised with the correct subnet mask.
  7. Configure passive interfaces for all interfaces where OSPF neighbors are not expected.
  8. Adjust OSPF Hello and Dead Intervals:
    • Between R1 & R5:
      • Hello Interval: 250 milliseconds (Note: PDF says "ip ospf dead-interval minimal hello-multiplier 4" which implies hello is 250ms if dead is 1s)
      • Dead Interval: 1 second
  9. Set MTU to 1400 on R7's interface connecting to R3.
  10. Disable DR & BDR elections between R4 and R8.
  11. Configure the EIGRP domain consisting of R8 and R9, as shown in the topology, and set up redistribution between OSPF and EIGRP:
    • On R8, ensure bidirectional redistribution of EIGRP routes into OSPF and vice versa.
  12. Verify the Type-4 and Type-5 LSAs generated due to redistribution:
    • Type-4 LSAs for the ASBR router.
    • Type-5 LSAs for the redistributed external routes.
  13. Ensure end-to-end communication across all areas and external routes.
  14. Verify the number of LSAs in each area:
    • Count and identify LSA Types 1, 2, 3, 4, and 5 across Areas 0, 1, 2, 3, and 4.

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 1.1.1.1 255.255.255.255
interface Ethernet0/0
 ip address 12.1.1.1 255.255.255.0
interface Ethernet0/1
 ip address 192.168.1.1 255.255.255.240
hostname R2

interface Loopback0
 ip address 2.2.2.2 255.255.255.255
interface Ethernet0/0
 ip address 12.1.1.2 255.255.255.0
interface Ethernet0/1
 ip address 192.168.2.2 255.255.255.192
hostname R3

interface Loopback0
 ip address 3.3.3.3 255.255.255.255
interface Ethernet0/0
 ip address 12.1.1.3 255.255.255.0
interface Ethernet0/1
 ip address 192.168.3.3 255.255.255.240
hostname R4

interface Loopback0
 ip address 4.4.4.4 255.255.255.255
interface Ethernet0/0
 ip address 12.1.1.4 255.255.255.0
interface Ethernet0/1
 ip address 192.168.4.4 255.255.255.192
hostname R5

interface Loopback0
 ip address 5.5.5.5 255.255.255.255
interface Loopback1
 ip address 10.5.1.1 255.255.255.0
interface Loopback2
 ip address 10.5.2.1 255.255.255.0
interface Ethernet0/0
 ip address 192.168.1.5 255.255.255.240
hostname R6

interface Loopback0
 ip address 6.6.6.6 255.255.255.255
interface Loopback1
 ip address 10.6.1.1 255.255.255.128
interface Loopback2
 ip address 10.6.2.1 255.255.255.128
interface Ethernet0/0
 ip address 192.168.2.6 255.255.255.192
hostname R7

interface Loopback0
 ip address 7.7.7.7 255.255.255.255
interface Loopback1
 ip address 10.7.1.1 255.255.255.0
interface Loopback2
 ip address 10.7.2.1 255.255.255.0
interface Ethernet0/0
 ip address 192.168.3.7 255.255.255.240
hostname R8

interface Loopback0
 ip address 8.8.8.8 255.255.255.255
interface Loopback1
 ip address 10.8.1.1 255.255.255.128
interface Loopback2
 ip address 10.8.2.1 255.255.255.128
interface Ethernet0/0
 ip address 192.168.4.8 255.255.255.192
interface Ethernet0/1
 ip address 89.1.1.1 255.255.255.252
hostname R9

interface Loopback0
 ip address 9.9.9.9 255.255.255.255
interface Loopback1
 ip address 10.9.1.1 255.255.255.0
interface Loopback2
 ip address 10.9.2.1 255.255.255.0
interface Ethernet0/0
 ip address 89.1.1.2 255.255.255.252

Verification Commands

  • show ip ospf neighbor
    • Check the OSPF adjacency states and confirm neighbor relationships.
  • show ip ospf database
    • View the OSPF link-state database and verify the presence of Type-4 and Type-5 LSAs.
  • show ip ospf interface brief
    • Confirm which interfaces are participating in OSPF.
  • show ip route ospf
    • Ensure the correct OSPF routes, including external routes, are being installed in the routing table.
  • show ip ospf
    • Check Router ID, OSPF process details, and ensure proper configuration.
  • show ip eigrp topology (Run on R8 or relevant EIGRP routers)
    • Verify the routes being redistributed into OSPF.

Expected Outcomes

  • OSPF should form adjacencies as per the topology.
  • The DR/BDR elections should reflect the desired setup.
  • MTU mismatches should be resolved.
  • Passive interfaces should not form neighbors.
  • Type-4 and Type-5 LSAs should be present in the OSPF database.
  • External routes from EIGRP should propagate throughout the OSPF domain.
  • OSPF LSAs should be correctly distributed among the areas.

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 1.1.1.1 255.255.255.255
 ip ospf network point-to-point
 ip ospf 1 area 0
interface Ethernet0/0
 ip address 12.1.1.1 255.255.255.0
 ip ospf 1 area 0
interface Ethernet0/1
 ip address 192.168.1.1 255.255.255.240
 ip ospf dead-interval minimal hello-multiplier 4
 ip ospf 1 area 1

router ospf 1
 router-id 1.1.1.1
 passive-interface Loopback0
hostname R2

interface Loopback0
 ip address 2.2.2.2 255.255.255.255
 ip ospf network point-to-point
 ip ospf 1 area 0
interface Ethernet0/0
 ip address 12.1.1.2 255.255.255.0
 ip ospf priority 100
 ip ospf 1 area 0
interface Ethernet0/1
 ip address 192.168.2.2 255.255.255.192
 ip ospf 1 area 2

router ospf 1
 router-id 2.2.2.2
 passive-interface Loopback0
hostname R3

interface Loopback0
 ip address 3.3.3.3 255.255.255.255
 ip ospf network point-to-point
 ip ospf 1 area 0
interface Ethernet0/0
 ip address 12.1.1.3 255.255.255.0
 ip ospf 1 area 0
interface Ethernet0/1
 ip address 192.168.3.3 255.255.255.240
 ip mtu 1400
 ip ospf 1 area 3

router ospf 1
 router-id 3.3.3.3
 passive-interface Loopback0
hostname R4

interface Loopback0
 ip address 4.4.4.4 255.255.255.255
 ip ospf network point-to-point
 ip ospf 1 area 0
interface Ethernet0/0
 ip address 12.1.1.4 255.255.255.0
 ip ospf priority 0
 ip ospf 1 area 0
interface Ethernet0/1
 ip address 192.168.4.4 255.255.255.192
 ip ospf network point-to-point
 ip ospf 1 area 4

router ospf 1
 router-id 4.4.4.4
 passive-interface Loopback0
hostname R5

interface Loopback0
 ip address 5.5.5.5 255.255.255.255
 ip ospf network point-to-point
 ip ospf 1 area 1
interface Loopback1
 ip address 10.5.1.1 255.255.255.0
 ip ospf network point-to-point
 ip ospf 1 area 1
interface Loopback2
 ip address 10.5.2.1 255.255.255.0
 ip ospf network point-to-point
 ip ospf 1 area 1
interface Ethernet0/0
 ip address 192.168.1.5 255.255.255.240
 ip ospf dead-interval minimal hello-multiplier 4
 ip ospf 1 area 1

router ospf 1
 router-id 5.5.5.5
 passive-interface Loopback0
 passive-interface Loopback1
 passive-interface Loopback2
hostname R6

interface Loopback0
 ip address 6.6.6.6 255.255.255.255
 ip ospf network point-to-point
 ip ospf 1 area 2
interface Loopback1
 ip address 10.6.1.1 255.255.255.128
 ip ospf network point-to-point
 ip ospf 1 area 2
interface Loopback2
 ip address 10.6.2.1 255.255.255.128
 ip ospf network point-to-point
 ip ospf 1 area 2
interface Ethernet0/0
 ip address 192.168.2.6 255.255.255.192
 ip ospf 1 area 2

router ospf 1
 router-id 6.6.6.6
 passive-interface Loopback0
 passive-interface Loopback1
 passive-interface Loopback2
hostname R7

interface Loopback0
 ip address 7.7.7.7 255.255.255.255
 ip ospf network point-to-point
 ip ospf 1 area 3
interface Loopback1
 ip address 10.7.1.1 255.255.255.0
 ip ospf network point-to-point
 ip ospf 1 area 3
interface Loopback2
 ip address 10.7.2.1 255.255.255.0
 ip ospf network point-to-point
 ip ospf 1 area 3
interface Ethernet0/0
 ip address 192.168.3.7 255.255.255.240
 ip mtu 1400
 ip ospf 1 area 3

router ospf 1
 router-id 7.7.7.7
 passive-interface Loopback0
 passive-interface Loopback1
 passive-interface Loopback2
hostname R8

interface Loopback0
 ip address 8.8.8.8 255.255.255.255
 ip ospf network point-to-point
 ip ospf 1 area 4
interface Loopback1
 ip address 10.8.1.1 255.255.255.128
 ip ospf network point-to-point
 ip ospf 1 area 4
interface Loopback2
 ip address 10.8.2.1 255.255.255.128
 ip ospf network point-to-point
 ip ospf 1 area 4
interface Ethernet0/0
 ip address 192.168.4.8 255.255.255.192
 ip ospf network point-to-point
 ip ospf 1 area 4
interface Ethernet0/1
 ip address 89.1.1.1 255.255.255.252

router ospf 1
 router-id 8.8.8.8
 redistribute eigrp 10 subnets
 passive-interface Loopback0
 passive-interface Loopback1
 passive-interface Loopback2

router eigrp 10
 network 89.1.1.1 0.0.0.0
 redistribute ospf 1 metric 1 1 1 1 1
hostname R9

interface Loopback0
 ip address 9.9.9.9 255.255.255.255
interface Loopback1
 ip address 10.9.1.1 255.255.255.0
interface Loopback2
 ip address 10.9.2.1 255.255.255.0
interface Ethernet0/0
 ip address 89.1.1.2 255.255.255.252

router eigrp 10
 network 9.9.9.9 0.0.0.0
 network 10.9.1.1 0.0.0.0
 network 10.9.2.1 0.0.0.0
 network 89.1.1.2 0.0.0.0
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