Back
Lesson 4 of 5

Basic Redistribution

Lab Objectives

  • Configure basic EIGRP (AS 111) and OSPF (process 1) on the base topology and advertise local networks.
  • Configure mutual redistribution between OSPF and EIGRP on the router that connects the two domains.
  • Understand and verify the role of seed metrics when redistributing into EIGRP and confirm routes are learned in both protocols.

Base ASCII Topology (use this EXACT topology and IPs for the lab):

                [Internet]
               203.0.113.1
                    |
               R1 (Gateway)
              Gi0/0: 10.10.10.1
              Gi0/1: 10.10.20.1
              Gi0/2: 10.10.30.1
              /     |     \
           R2      R3      R4

Gi0/0: 10.10.10.2 | Gi0/0: 10.10.30.2 Gi0/1: 10.10.40.1 | / \ | S1 S2 S3 / \ | /
PC1 PC2 PC3 PC4 PC5

IP scheme (use these EXACT networks):

  • 10.10.10.0/24 — R1-R2 link
  • 10.10.20.0/24 — R1-R3 link
  • 10.10.30.0/24 — R1-R4 link
  • 10.10.40.0/24 — R2-S1 link
  • 192.168.1.0/24 — VLAN 10 (Sales) — represented here by R2 loopback
  • 192.168.2.0/24 — VLAN 20 (Engineering) — represented here by R2 loopback
  • 192.168.3.0/24 — VLAN 30 (Management) — represented here by R3 loopback
  • 203.0.113.0/24 — Public/Internet simulation

Key concepts introduced: Redistribution, ASBR (Autonomous System Boundary Router), Seed Metric.

Tip: Think of an ASBR as a border post that translates routes between two routing "languages." When you redistribute into EIGRP, you must provide a seed metric because EIGRP needs a full composite metric to place the external route into its topology — without it, EIGRP cannot compare or install the external route.

Lab Tasks (Try It Yourself First!)

Complete these tasks WITHOUT looking at the solution below. Use ? and show commands to figure it out.

Task 1: Configure EIGRP on R2

Enable EIGRP AS 111 on R2 so it advertises:

  • 10.10.10.0/24 (link to R1)
  • 10.10.40.0/24 (LAN toward S1)
  • Loopbacks representing VLANs: 192.168.1.1/24 and 192.168.2.1/24

(do NOT paste commands here — just plan the network statements)

Task 2: Configure OSPF on R1 and R3

Enable OSPF process 1 and advertise:

  • On R1: 10.10.10.0/24, 10.10.20.0/24, 10.10.30.0/24
  • On R3: advertise 10.10.20.0/24 and create a loopback 192.168.3.1/24 to simulate VLAN 30

Task 3: Configure Mutual Redistribution on R1 (ASBR)

On R1 run both EIGRP 111 (for the R1–R2 link) and OSPF 1 (for the R1–R3/R4 links). Configure mutual route redistribution so OSPF routes are available in EIGRP and EIGRP routes are available in OSPF. Use the seed metric values shown in the reference when redistributing into EIGRP.

Think About It: If you redistribute R2's 192.168.1.0/24 into OSPF, why must you also provide a metric when redistributing OSPF routes into EIGRP? What would happen if you omitted the metric?

Lab Solution

Task 1 Solution: Configure EIGRP on R2

What we are doing: Configure EIGRP AS 111 on R2 to advertise the connected LANs and loopbacks. This creates the EIGRP domain for R2 and allows R1 (when configured for EIGRP on the shared link) to form an adjacency.

! On R2
interface GigabitEthernet0/0
 ip address 10.10.10.2 255.255.255.0
!
interface GigabitEthernet0/1
 ip address 10.10.40.1 255.255.255.0
!
interface Loopback10
 ip address 192.168.1.1 255.255.255.0
!
interface Loopback20
 ip address 192.168.2.1 255.255.255.0
!
router eigrp 111
 network 10.10.10.0
 network 10.10.40.0
 network 192.168.1.0
 network 192.168.2.0

What each command does and why it matters:

  • interface ... ip address ... — assigns the IPs to interfaces so EIGRP can bring them into the routing process; without interface IPs there is nothing to advertise.
  • interface Loopback... ip address ... — loopbacks represent internal networks (VLANs) that should be advertised into EIGRP.
  • router eigrp 111 — enters EIGRP config for AS 111.
  • network X.X.X.X — enables EIGRP on interfaces whose IPs fall into the listed networks; this causes R2 to advertise those prefixes.

Verify:

! On R2
show ip route

Expected output excerpt (you should see local connected prefixes and EIGRP entries):

Gateway of last resort is not set

C    10.10.10.0/24 is directly connected, GigabitEthernet0/0
C    10.10.40.0/24 is directly connected, GigabitEthernet0/1
L    192.168.1.1/32 is directly connected, Loopback10
L    192.168.2.1/32 is directly connected, Loopback20

Why this matters: Confirming the networks exist locally before redistribution prevents confusion — you must have the original networks present in their native protocol before trying to redistribute them.

Task 2 Solution: Configure OSPF on R1 and R3

What we are doing: Configure OSPF process 1 on R1 and R3 and advertise the point-to-point links and R3’s loopback (192.168.3.1/24).

! On R1
interface GigabitEthernet0/0
 ip address 10.10.10.1 255.255.255.0
!
interface GigabitEthernet0/1
 ip address 10.10.20.1 255.255.255.0
!
interface GigabitEthernet0/2
 ip address 10.10.30.1 255.255.255.0
!
router ospf 1
 network 10.10.10.0 0.0.0.255 area 0
 network 10.10.20.0 0.0.0.255 area 0
 network 10.10.30.0 0.0.0.255 area 0

! On R3
interface GigabitEthernet0/0
 ip address 10.10.20.2 255.255.255.0
!
interface Loopback30
 ip address 192.168.3.1 255.255.255.0
!
router ospf 1
 network 10.10.20.0 0.0.0.255 area 0
 network 192.168.3.0 0.0.0.255 area 0

What each command does and why it matters:

  • Interface IPs ensure OSPF has neighbors on the correct networks.
  • router ospf 1 starts OSPF process 1.
  • network ... area 0 tells OSPF which interfaces to enable; area 0 is the OSPF backbone — in production the backbone must connect OSPF routers reliably.

Verify:

! On R3
show ip route ospf

Expected output excerpt:

O    10.10.20.0/24 [110/11] via 10.10.20.1, 00:00:12, GigabitEthernet0/0
C    192.168.3.0/24 is directly connected, Loopback30

In production: OSPF is commonly used inside the data center or campus; the backbone (area 0) transports inter-area traffic and external routes redistributed into OSPF appear as type-5 LSAs (external).

Task 3 Solution: Configure Mutual Redistribution on R1 (ASBR)

What we are doing: R1 will be the ASBR — it runs both EIGRP and OSPF and performs mutual redistribution. When redistributing OSPF into EIGRP, EIGRP requires a seed metric (composite metric). When redistributing EIGRP into OSPF, use the subnets keyword so OSPF advertises the external subnets.

! On R1 - enable EIGRP for the R1-R2 link
router eigrp 111
 network 10.10.10.0
 redistribute ospf 1 metric 10 10 10 10 10

! On R1 - OSPF already configured; add redistribution of EIGRP into OSPF
router ospf 1
 redistribute eigrp 111 subnets

What each command does and why it matters:

  • router eigrp 111 / network 10.10.10.0 — brings the R1–R2 interface into EIGRP so R1 peers with R2.
  • redistribute ospf 1 metric 10 10 10 10 10 — takes routes known via OSPF and injects them into EIGRP AS 111 with a seed metric. This is required because EIGRP uses a composite metric; without the metric the router would not accept/advertise the redistributed OSPF routes.
  • router ospf 1 / redistribute eigrp 111 subnets — injects EIGRP routes into OSPF. The subnets keyword ensures OSPF advertises all subnet masks (not only classful networks).

Verify:

! On R2 (EIGRP-only router) check routing table for 192.168.3.0/24 (learned via EIGRP as external)
show ip route 192.168.3.0

Expected output excerpt (EIGRP external):

Routing entry for 192.168.3.0/24
  Known via "eigrp 111", distance 170, metric 3840000, type external
  Redistributing via eigrp 111
  Advertised by external route
  * 10.10.10.1 (GigabitEthernet0/0)

! On R3 (OSPF-only router) check routing table for 192.168.1.0/24 (learned via OSPF external)
show ip route 192.168.1.0

Expected output excerpt (OSPF external type 2):

O E2 192.168.1.0/24 [110/20] via 10.10.20.1, 00:00:05, GigabitEthernet0/0

Why this matters: These verifications confirm routes learned from the opposite protocol are present. The EIGRP "external" entry indicates routes that originated outside EIGRP; OSPF's "O E2" shows an external Type-2 LSA from redistribution.

Important note: When redistributing between protocols, always plan metrics and loop prevention (tags/filters) in production. Uncontrolled mutual redistribution can cause routing loops or route feedback.

Troubleshooting Scenario

Scenario: Redistribution configured but routes are not appearing in EIGRP

Symptom: On R2 you do not see R3's 192.168.3.0/24 in the routing table after configuring redistribution on R1.

Your task: Find and fix the issue.

Hint: Check the redistribution commands on R1 and remember EIGRP requires a metric value when importing routes from another protocol.

Solution:

  • Show current redistribution on R1:
! On R1
show running-config | section router eigrp
  • If redistribute ospf 1 is missing the metric parameters, add them:
! On R1
router eigrp 111
 redistribute ospf 1 metric 10 10 10 10 10
  • Verify on R2:
show ip route 192.168.3.0

Explanation: EIGRP will not install redistributed routes without a seed metric. Adding the metric provides the composite metric values EIGRP needs to evaluate and install the external route.

Verification Checklist

  • R2 has EIGRP 111 configured and is advertising 192.168.1.0/24 and 192.168.2.0/24.
  • R1 has OSPF process 1 and advertises the 10.10.10/20/30 links.
  • R1 performs mutual redistribution: redistribute ospf 1 metric ... under EIGRP and redistribute eigrp 111 subnets under OSPF.
  • R3 (OSPF) sees 192.168.1.0/24 as an OSPF external (O E2).
  • R2 (EIGRP) sees 192.168.3.0/24 as an EIGRP external route.

Common Mistakes

SymptomCauseFix
No EIGRP external routes on R2redistribute ospf on R1 missing metricAdd redistribute ospf 1 metric 10 10 10 10 10 under router eigrp 111 on R1
OSPF shows only a summary or no external LSAsredistribute eigrp on R1 missing subnetsAdd redistribute eigrp 111 subnets under router ospf 1 on R1
Route flapping or loops after redistributionMutual redistribution without tagging or filteringIn production, use route tags or route-maps to prevent re-injection loops (advanced)

Challenge Task

Create a simple route-tagging or route-map based filter so that routes learned from EIGRP and redistributed into OSPF are not readvertised back into EIGRP. Do this without step-by-step guidance — your goal: prevent route feedback in a mutual-redistribution setup while still allowing the opposite-domain prefixes to be reachable.

Real-world insight: In production, mutual redistribution usually includes route tagging and filtering to prevent feedback loops and to control which external networks are accepted. This lab focuses on the mechanics and necessity of seed metrics and the basic verification steps.

Practice with Hands-On Labs

30 step-by-step labs for CCNA, CCNP Enterprise & Security