## **Objective**

Controlled and **loop-free route redistribution between OSPF (HQ1) and EIGRP (HQ2)**, implemented on the boundary routers **CR3 and CR4**, based on a **proven, working configuration logic**.

Detailed goals:

- Mutual reachability between HQ1 and HQ2 networks
- Prevention of routing loops
- Clear separation of routing domains using tags
- Redistribution of **only explicitly defined networks**
- Preservation of summary routing

---

## **1. Redistribution Core Principle**

- Redistribution is **bidirectional**
- Implemented only on **CR3 and CR4**
- Controlled via:
    - prefix-lists
    - route-maps
    - route tags

Tags used:

- **Tag 12** → HQ1 → EIGRP
- **Tag 34** → HQ2 → OSPF

These tags are actively checked to prevent re-redistribution loops.

---

## **2. Prefix-Lists**

### **2.1 HQ1-SUBNETS (OSPF → EIGRP)**

Contains all networks that are allowed to be propagated from HQ1 to HQ2.

```
ip prefix-list HQ1-SUBNETS permit 10.10.0.0/24 le 32
ip prefix-list HQ1-SUBNETS permit 10.10.100.0/22
```

---

### **2.2 HQ2-SUBNETS (EIGRP → OSPF)**

Contains all networks that are allowed to be propagated from HQ2 to HQ1.

```
ip prefix-list HQ2-SUBNETS permit 10.11.100.0/22
ip prefix-list HQ2-SUBNETS permit 10.10.0.11/32
ip prefix-list HQ2-SUBNETS permit 10.10.0.12/32
ip prefix-list HQ2-SUBNETS permit 10.10.0.13/32
```

---

## **3. Route-Maps**

### **3.1 OSPF → EIGRP (HQ1 → HQ2)**

- Blocks all routes with tag 34 (return traffic)
- Sets tag 12 for HQ1 routes

```
route-map OSPF_TO_EIGRP deny 5
 match tag 34

route-map OSPF_TO_EIGRP permit 10
 match ip address prefix-list HQ1-SUBNETS
 set tag 12
```

---

### **3.2 EIGRP → OSPF (HQ2 → HQ1)**

- Blocks all routes with tag 12 (return traffic)
- Sets tag 34 for HQ2 routes

```
route-map EIGRP_TO_OSPF deny 5
 match tag 12

route-map EIGRP_TO_OSPF permit 10
 match ip address prefix-list HQ2-SUBNETS
 set tag 34
```

---

## **4. Redistribution in the Routing Processes**

### **4.1 OSPF → EIGRP (CR3 / CR4)**

```
router eigrp WSC2024
 address-family ipv4 unicast autonomous-system 100
  topology base
   redistribute ospf 100 metric 1000000 1000 255 1 1500 route-map OSPF_TO_EIGRP
  exit-af-topology
 exit-address-family
```

---

### **4.2 EIGRP → OSPF (CR3 / CR4)**

```
router ospf 100
 redistribute eigrp 100 subnets route-map EIGRP_TO_OSPF
```

---

## **5. Verification**

```
show ip route ospf
show ip route eigrp
show route-map
```

Expected:

- HQ1 routes appear in EIGRP with **tag 12**
- HQ2 routes appear in OSPF with **tag 34**
- No double-redistributed routes
- No routing loops

---

## **Status**

- Redistribution between OSPF and EIGRP is stable
- Loop prevention implemented via consistent tagging
- Networks propagated selectively and under control
- Solution fully based on a productive, working configuration
- Suitable for scoring and competition use