Default Route in EIGRP: Distributing Internet Access Automatically
Lab Objective
- Configure a default route and distribute it through the EIGRP routing protocol
🛠️ Equipment Needed for This Lab
- 2 Cisco routers
- 2 Cisco 2960 switches
- 2 PCs
- 1 internet access connection
Router Interface Configuration
| Router | Interface | IP Address | Subnet Mask | Serial Type |
|---|---|---|---|---|
| Router 1 | FastEthernet 0/0 | 192.168.14.1 | 255.255.255.0 | — |
| Router 1 | Serial 0/0 | 192.168.15.1 | 255.255.255.0 | DCE |
| Router 2 | Serial 0/0 | 192.168.15.2 | 255.255.255.0 | DTE |
| Router 2 | FastEthernet 0/0 | 192.168.16.1 | 255.255.255.0 | — |
| Router 2 | FastEthernet 1/1 | 192.168.100.2 | 255.255.255.0 | — |
ISP Router Interface Configuration
| Router | Interface | IP Address | Subnet Mask |
|---|---|---|---|
| ISP | FastEthernet 1/1 | 192.168.100.1 | 255.255.255.0 |
PC Configuration
| Computer | IP Address | Subnet Mask | Default Gateway |
|---|---|---|---|
| PC1 | 192.168.14.2 | 255.255.255.0 | 192.168.14.1 |
| PC2 | 192.168.16.2 | 255.255.255.0 | 192.168.16.1 |
Why Distribute the Default Route?
In this lab, we’ll define the default route only on the router directly connected to the internet. Then we’ll advertise it through EIGRP — a dynamic routing protocol — so every router in the network learns the default route automatically.
Simply put: the default route defined on Router2 (directly connected to the ISP) is injected into EIGRP and sent as an update message to all other routers.
Step 1: Configure Router1 and Router2 and Set IP Addresses on Router Interfaces
Configure FastEthernet 0/0 on Router1:
Router1#config t Router1(config)#interface fastEthernet 0/0 Router1(config-if)#ip address 192.168.14.1 255.255.255.0 Router1(config-if)#no shutdown
Configure Serial 0/0 on Router1:
Router1(config)#interface serial 0/0 Router1(config-if)#ip address 192.168.15.1 255.255.255.0 Router1(config-if)#clock rate 64000 Router1(config-if)#no shutdown
Configure FastEthernet 0/0 on Router2:
Router2#config t Router2(config)#interface fastEthernet 0/0 Router2(config-if)#ip address 192.168.16.1 255.255.255.0 Router2(config-if)#no shutdown
Configure FastEthernet 1/1 on Router2 (facing the ISP):
Router2(config)#interface fastEthernet 1/1 Router2(config-if)#ip address 192.168.100.2 255.255.255.0 Router2(config-if)#no shutdown
Configure Serial 0/0 on Router2:
Router2(config)#interface serial 0/0 Router2(config-if)#ip address 192.168.15.2 255.255.255.0 Router2(config-if)#no shutdown
Step 2: Configure the EIGRP Routing Protocol on Router1 and Router2
Configure EIGRP on Router1:
Router1#config t Router1(config)#router eigrp 100 Router1(config-router)#network 192.168.14.0 255.255.255.0 Router1(config-router)#network 192.168.15.0 255.255.255.0 Router1(config-router)#exit Router1(config)#exit
Configure EIGRP on Router2:
Router2#config t Router2(config)#router eigrp 100 Router2(config-router)#network 192.168.15.0 255.255.255.0 Router2(config-router)#network 192.168.16.0 255.255.255.0 Router2(config-router)#exit Router2(config)#exit
Step 3: Configure the Default Route on Router2
Configure a default route so all unknown packets go to the ISP router:
Router2#config t Router2(config)#ip route 0.0.0.0 0.0.0.0 192.168.100.1
Any packet with any destination (0.0.0.0) and any subnet mask (0.0.0.0) that has no matching route is sent to the ISP router at 192.168.100.1.
Note: Configure the default route only on the router directly connected to the internet. No manual default route is needed on other routers.
Step 4: Inject the Default Route into EIGRP for Distribution to Other Routers
Now we’ll advertise the default route defined on Router2 through EIGRP so every router learns it automatically. Other routers will receive the default route through EIGRP updates and add it to their routing tables.
Use the following command on Router2 to redistribute the default route into EIGRP:
Router2(config)#router eigrp 100 Router2(config-router)#redistribute static
This command injects the default route written on Router2 into EIGRP. The default route is sent to other routers through EIGRP update packets.
Step 5: View the Routing Tables on Router1 and Router2
Run show ip route on Router1:
Router1#show ip route Gateway of last resort is 192.168.15.2 to network 0.0.0.0 C 192.168.14.0/24 is directly connected, FastEthernet0/0 C 192.168.15.0/24 is directly connected, Serial0/0 D 192.168.16.0/24 [90/20514560] via 192.168.15.2, 01:26:47, Serial0/0 D*EX 0.0.0.0/0 [170/20537600] via 192.168.15.2, 01:26:26, Serial0/0
In the show ip route output above, Router1 has learned a default route through EIGRP — marked as D*EX in the routing table.
Run show ip route on Router2:
Router2#show ip route D 192.168.14.0/24 [90/20514560] via 192.168.15.1, 01:29:44, Serial0/0 C 192.168.15.0/24 is directly connected, Serial0/0 C 192.168.16.0/24 is directly connected, FastEthernet0/0 C 192.168.100.0/24 is directly connected, FastEthernet1/1 S* 0.0.0.0/0 [1/0] via 192.168.100.1
❓ Why Do Router1 and Router2 Show Different Default Route Codes?
Router1 shows the default route as D*EX — learned through EIGRP as an external route with AD 170. Router2 shows it as S* — statically configured with AD 1. Both point to the same destination, but they’re added differently.
Router1 Final Configuration
hostname Router1 ! ! ! interface fastEthernet 0/0 ip address 192.168.14.1 255.255.255.0 no shutdown ! ! ! interface Serial 0/0 ip address 192.168.15.1 255.255.255.0 clock rate 64000 no shutdown ! ! ! router eigrp 100 network 192.168.14.0 network 192.168.15.0 ! ! End
Router2 Final Configuration
hostname Router2 ! ! ! interface fastEthernet 0/0 ip address 192.168.16.1 255.255.255.0 no shutdown ! ! ! interface fastEthernet 1/1 ip address 192.168.100.2 255.255.255.0 no shutdown ! ! ! interface Serial 0/0 ip address 192.168.15.2 255.255.255.0 no shutdown ! ! ! router eigrp 100 redistribute static network 192.168.15.0 network 192.168.16.0 ! ! ip route 0.0.0.0 0.0.0.0 192.168.100.1 ! ! End
Command Reference
| Command | Description |
|---|---|
| Router2(config)#ip route 0.0.0.0 0.0.0.0 192.168.100.1 | Configures a static default route pointing to the ISP router. |
| Router2(config-router)#redistribute static | Injects the static default route into EIGRP so neighbors learn it automatically. |
| Router1#show ip route | Displays the routing table, including the D*EX default route learned via EIGRP. |
| Router2#show ip route | Displays the routing table, including the S* default route configured statically. |
Routing Table Codes
| Code | Meaning | How It’s Added |
|---|---|---|
| C | Connected | Automatically |
| D | EIGRP | Dynamic — internal EIGRP |
| D*EX | EIGRP External | Dynamic — redistributed into EIGRP |
| S* | Static Default | Manually — ip route 0.0.0.0 |
| R* | RIP Default | Dynamic — learned via RIP |
The D*EX code: D = EIGRP, * = candidate default, EX = external route (redistributed from static or another protocol). External EIGRP routes have AD 170.
Default Route Distribution Best Practices
- Configure the default route only on the ISP-facing router.
- Use
redistribute staticto inject the default route into EIGRP. - Verify with
show ip route— Router1 should show D*EX. - Check that the ISP-facing router shows S* for its locally configured default route.
- External EIGRP routes have AD 170 — higher than internal EIGRP (90).
- Test with ping from internal PCs to an external destination.
✅ Key Takeaways
- Configure the default route only on the ISP-facing router.
- Use
redistribute staticto advertise the default route through EIGRP. - All other routers learn the default route automatically.
- Router1 shows the default route as D*EX — external EIGRP route with AD 170.
- Router2 shows the default route as S* — statically configured with AD 1.
- This approach simplifies default route management in large networks.
- No need to manually configure the default route on every router.
- EIGRP automatically propagates the default route through its update messages.
