Monday, May 11, 2026

Complete Cisco Nexus OSPF & EIGRP Redistribution Lab Configuration Guide

Cisco Nexus OSPF & EIGRP Redistribution Lab Guide

Complete Cisco Nexus OSPF & EIGRP Redistribution Lab Guide

This advanced Cisco networking tutorial explains how to configure OSPF and EIGRP together in a multi-protocol enterprise topology using Cisco routers and Cisco Nexus switches. The lab covers multi-area OSPF, OSPF router IDs, loopback advertisement, point-to-point loopbacks, redistribution between OSPF and EIGRP, and enterprise routing verification.

Main Learning Objective: This lab teaches how enterprise networks integrate multiple routing protocols together using redistribution and hierarchical OSPF design.

Table of Contents

1. OSPF and EIGRP Lab Overview

Open Shortest Path First (OSPF) is a link-state routing protocol commonly used in enterprise environments. Unlike EIGRP, OSPF uses the SPF algorithm to calculate shortest paths.

This lab demonstrates:

  • OSPF Area configuration
  • OSPF Router IDs
  • OSPF loopback advertisements
  • Point-to-point loopback behavior
  • Multi-area OSPF
  • EIGRP and OSPF redistribution
  • End-to-end routing verification

OSPF Administrative Distance

OSPF routes use:

\[ AD = 110 \]

Lower values are preferred over higher administrative distances.

2. Task 0 - Remove EIGRP Configurations

Before enabling OSPF, all EIGRP configurations from previous labs must be removed.

Important: Removing old configurations prevents route conflicts and overlapping protocol advertisements.

Example EIGRP Removal

no router eigrp NX-12
no router eigrp NEXUS
no feature eigrp

3. Understanding OSPF Fundamentals

OSPF is a hierarchical link-state routing protocol that organizes networks into areas.

Main OSPF Concepts

  • Router ID
  • Area 0 Backbone
  • LSA Flooding
  • SPF Algorithm
  • ABR (Area Border Router)
  • ASBR (Autonomous System Boundary Router)

OSPF Cost Formula

OSPF uses:

\[ \text{Cost} = \frac{\text{Reference Bandwidth}}{\text{Interface Bandwidth}} \]

Default Cisco reference bandwidth:

\[ 100000000 \]

Backbone Rule: All OSPF areas must connect to Area 0 either physically or virtually.

4. Task 1 - Configure EIGRP AS 12

R1 and R2 continue using EIGRP Autonomous System 12.

R1 Configuration

router eigrp NX-12
 address-family ipv4 unicast autonomous-system 12
 eigrp router-id 10.1.1.1
 network 192.1.12.0

R2 Configuration

router eigrp NX-12
 address-family ipv4 unicast autonomous-system 12
 eigrp router-id 10.1.1.2
 network 192.1.12.0
 network 2.0.0.0
 network 10.1.1.2 0.0.0.0
 network 100.1.2.0 0.0.0.255
EIGRP Neighbor Verification 
R1# show ip eigrp neighbors

Address          Interface
192.1.12.2       Ethernet0/0

5. Task 2 - Configure OSPF Area 0

R1, NX-01, and NX-02 participate in OSPF Area 0.

Important: Area 0 is the OSPF backbone area and is mandatory in multi-area OSPF deployments.

R1 OSPF Configuration

router ospf 1
 router-id 0.0.0.1
 network 192.1.10.0 0.0.0.255 area 0
 network 192.1.20.0 0.0.0.255 area 0
 network 1.0.0.0 0.255.255.255 area 0
 network 10.1.1.1 0.0.0.0 area 0
 network 100.1.1.0 0.0.0.255 area 0

Loopback Point-to-Point Configuration

interface loopback0
 ip ospf network point-to-point

interface loopback1
 ip ospf network point-to-point

interface loopback10
 ip ospf network point-to-point

NX-01 OSPF Configuration

feature ospf

router ospf 1
 router-id 0.0.0.21

interface loopback0
 ip router ospf 1 area 0
 ip ospf network point-to-point

interface vlan10
 ip router ospf 1 area 0

NX-02 OSPF Configuration

feature ospf

router ospf 1
 router-id 0.0.0.22

interface loopback0
 ip router ospf 1 area 0
 ip ospf network point-to-point

interface vlan20
 ip router ospf 1 area 0
Why Use Point-to-Point on Loopbacks?

By default, OSPF advertises loopbacks as /32 host routes. Using: 

ip ospf network point-to-point

forces OSPF to advertise the actual subnet mask configured on the interface.

6. Task 3 - Configure OSPF Area 10

NX-01 and NX-03 participate in OSPF Area 10.

NX-01 Area 10 Configuration

interface loopback1
 ip router ospf 1 area 10
 ip ospf network point-to-point

interface loopback10
 ip router ospf 1 area 10
 ip ospf network point-to-point

interface vlan30
 ip router ospf 1 area 10

NX-03 Configuration

feature ospf

router ospf 1
 router-id 0.0.0.23

interface loopback0
 ip router ospf 1 area 10
 ip ospf network point-to-point

interface loopback1
 ip router ospf 1 area 10
 ip ospf network point-to-point

interface loopback10
 ip router ospf 1 area 10
 ip ospf network point-to-point

interface vlan30
 ip router ospf 1 area 10

OSPF SPF Calculation

If:

  • Path A cost = 10
  • Path B cost = 20

Then:

\[ 10 < 20 \]

OSPF selects Path A.

7. Task 4 - Configure OSPF Area 20

NX-02 and NX-04 participate in OSPF Area 20.

NX-02 Configuration

interface loopback1
 ip router ospf 1 area 20
 ip ospf network point-to-point

interface loopback10
 ip router ospf 1 area 20
 ip ospf network point-to-point

interface ethernet1/5
 ip router ospf 1 area 20

NX-04 Configuration

feature ospf

router ospf 1
 router-id 0.0.0.24

interface loopback0
 ip router ospf 1 area 20
 ip ospf network point-to-point

interface loopback1
 ip router ospf 1 area 20
 ip ospf network point-to-point

interface loopback10
 ip router ospf 1 area 20
 ip ospf network point-to-point

interface ethernet1/6
 ip router ospf 1 area 20
ABR Function: NX-01 and NX-02 function as Area Border Routers because they connect Area 0 to other OSPF areas.

8. Task 5 - Configure Redistribution

R1 redistributes routes between EIGRP and OSPF.

R1 Redistribution Configuration

router eigrp NX-12
 address-family ipv4 unicast autonomous-system 12
 topology base
 redistribute ospf 1 metric 10 10 10 10 10

OSPF Redistribution Configuration

router ospf 1
 redistribute eigrp 12

EIGRP Redistribution Metric Mathematics

Redistribution requires:

  • Bandwidth
  • Delay
  • Reliability
  • Load
  • MTU

Metric values:

\[ 10,10,10,10,10 \]

These parameters create a valid composite EIGRP metric.

Important: EIGRP requires a metric during redistribution because external routes do not automatically contain EIGRP metric values.

9. Verification Commands

Command Purpose
show ip ospf neighbor Displays OSPF neighbors
show ip ospf database Displays LSDB
show ip route ospf Displays OSPF routes
show ip route eigrp Displays EIGRP routes
ping Connectivity verification
OSPF Neighbor Verification 
R1# show ip ospf neighbor

Neighbor ID     State
0.0.0.21        FULL
0.0.0.22        FULL
Redistribution Verification 
R2# show ip route

O E2 121.121.121.0/8
O E2 123.123.123.0/8

10. OSPF Mathematics & Metric Calculations

OSPF Cost Example

If interface bandwidth:

\[ 100000000 \text{ bps} \]

Then:

\[ \frac{100000000}{100000000}=1 \]

OSPF cost equals:

\[ 1 \]

Summed Path Cost

If:

  • Link 1 cost = 10
  • Link 2 cost = 20
  • Link 3 cost = 5

Total SPF path:

\[ 10 + 20 + 5 = 35 \]

LSA Flooding Calculation

If:

  • 5 routers exist in Area 0
  • Each router sends 3 LSAs

Total LSAs:

\[ 5 \times 3 = 15 \]

11. OSPF Troubleshooting

Common OSPF issues include:

  • Area mismatch
  • Hello/dead timer mismatch
  • Authentication mismatch
  • Incorrect wildcard masks
  • Duplicate router IDs
  • Missing Area 0 connectivity
Golden Rule: OSPF neighbors must match Area ID, timers, subnet, and authentication settings.

Troubleshooting Commands

show ip ospf neighbor
show ip ospf interface
show ip ospf database
show ip protocols
debug ip ospf adj
Common OSPF Neighbor Failure 
%OSPF-4-ERRRCV:
Received invalid packet from neighbor

Usually caused by:

  • Area mismatch
  • Authentication mismatch
  • MTU mismatch

13. Conclusion

This Cisco Nexus OSPF and EIGRP redistribution lab demonstrated:

  • OSPF Area configuration
  • Router IDs
  • Loopback advertisement
  • Point-to-point loopbacks
  • Multi-area OSPF
  • EIGRP redistribution
  • OSPF redistribution
  • End-to-end routing verification

Enterprise networks often require multiple routing protocols to coexist. Redistribution enables seamless communication between these routing domains.

Final Learning Point: OSPF provides scalable hierarchical routing, while redistribution allows multiple routing protocols to exchange routes efficiently. Mastering redistribution is one of the most important advanced routing skills in enterprise networking.
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