Packet Tracer Lab: Building a Network with EIGRP
If you are a non-technical student and have never worked with computer networks before, words like router, IP address, routing table, EIGRP, and subnet can sound complicated.
I felt the same way when I started.
In this lab, I built a small network using Cisco Packet Tracer and learned how three routers can communicate with each other using EIGRP.
The goal of this article is not just to give you commands to copy. I want to explain what each step means and why we are doing it.
1. What is Cisco Packet Tracer?
Cisco Packet Tracer is a program that lets you build and test computer networks on your computer.
Normally, if I wanted to practice with three Cisco routers, I would need three physical routers, cables, switches, and computers.
Packet Tracer gives me virtual versions of these devices.
So instead of buying hardware, I can create this:
PC1 ── Switch ── Router 1 ── Router 2 ── Router 3 ── Switch ── PC3
I can configure the devices and test whether they can communicate.
Think of Packet Tracer as a virtual networking laboratory.
2. What are we building?
Our first project contains three routers:
R1 R2 R3
🛜 🛜 🛜
| | |
PC1 ── Switch ────┘ | └──── Switch ── PC3
The routers are connected like this:
R1 ───────── R2 ───────── R3
Each router has its own job.
R1 connects to PC1's network.
R2 connects R1 and R3 together.
R3 connects to PC3's network.
Our final goal is:
PC1 → R1 → R2 → R3 → PC3
PC1 should eventually be able to communicate with PC3.
3. First, understand IP addresses
Before configuring anything, we need to understand IP addresses.
An IP address is like an address for a device.
For example:
PC1 = 192.168.1.10
You can think of this like a house address.
PC3 has:
PC3 = 192.168.3.10
It is like a house on a different street.
Our network will use these addresses:
| Device | Interface | IP Address |
|---|---|---|
| PC1 | NIC | 192.168.1.10 |
| R1 | G0/0 | 192.168.1.1 |
| R1 | G0/1 | 10.0.12.1 |
| R2 | G0/0 | 10.0.12.2 |
| R2 | G0/1 | 10.0.23.1 |
| R3 | G0/0 | 10.0.23.2 |
| R3 | G0/1 | 192.168.3.1 |
| PC3 | NIC | 192.168.3.10 |
Don't worry if these numbers look strange. We'll learn what they mean as we go.
4. Create the topology in Packet Tracer
Open Cisco Packet Tracer.
Add:
3 routers
2 switches
2 PCs
Connect them like this:
PC1
|
Switch
|
R1
|
R2
|
R3
|
Switch
|
PC3
The important part is that:
R1 ── R2 ── R3
are connected.
5. Configure Router 1
Click R1 and open the CLI.
The CLI is simply a place where we can type commands to control the router.
Start with:
enable
This gives us access to privileged commands.
Then:
configure terminal
This allows us to change the router's configuration.
Now give the router a name:
hostname R1
The prompt should now look something like:
R1(config)#
6. Give R1 its first IP address
We want R1's connection to the local network to use:
192.168.1.1
Enter:
interface gigabitEthernet 0/0
ip address 192.168.1.1 255.255.255.0
no shutdown
exit
What did we just do?
This command:
interface gigabitEthernet 0/0
means:
"I want to configure this particular connection on the router."
Then:
ip address 192.168.1.1 255.255.255.0
gives that connection an IP address.
And:
no shutdown
means:
"Turn this interface on."
Routers can have interfaces that are administratively turned off. no shutdown activates the interface.
7. Configure R1's connection to R2
R1 also needs an IP address for its connection to R2.
Enter:
interface gigabitEthernet 0/1
ip address 10.0.12.1 255.255.255.252
no shutdown
exit
Now R1 has two important connections:
PC1 network
192.168.1.1
|
R1
|
10.0.12.1
8. Check R1
Run:
show ip interface brief
You should see something similar to:
Interface IP-Address Status Protocol
GigabitEthernet0/0 192.168.1.1 up up
GigabitEthernet0/1 10.0.12.1 up up
The important thing is:
up / up
This means the interface is working.
9. Configure Router 2
Now we configure R2.
Enter:
enable
configure terminal
hostname R2
Configure the connection to R1:
interface gigabitEthernet 0/0
ip address 10.0.12.2 255.255.255.252
no shutdown
exit
Configure the connection to R3:
interface gigabitEthernet 0/1
ip address 10.0.23.1 255.255.255.252
no shutdown
exit
Now R2 is between R1 and R3:
R1 ───────── R2 ───────── R3
10.0.12 10.0.23
10. Configure Router 3
Now configure R3.
Enter:
enable
configure terminal
hostname R3
Configure the connection to R2:
interface gigabitEthernet 0/0
ip address 10.0.23.2 255.255.255.252
no shutdown
exit
Configure the local network:
interface gigabitEthernet 0/1
ip address 192.168.3.1 255.255.255.0
no shutdown
exit
Now our network looks like this:
192.168.1.0 192.168.3.0
Network Network
PC1 PC3
| |
SW1 SW3
| |
R1 ───────── R2 ───────────── R3
11. Test the connection
Before learning EIGRP, let's test what the routers currently know.
From R1:
ping 10.0.12.2
If you receive replies, R1 can communicate with R2.
You may see:
Success rate is 80 percent
The first packet can sometimes fail because the devices are learning each other's MAC addresses using ARP.
Try the ping again.
You should normally get:
Success rate is 100 percent
12. Why can't R1 reach R3 yet?
Try:
ping 10.0.23.2
You may get:
Success rate is 0 percent
Why?
Because R1 doesn't know where the 10.0.23.0 network is.
This is one of the most important ideas in networking.
A router needs a map.
That map is called the:
Routing table
13. Look at R1's routing table
Run:
show ip route
You should see routes similar to:
C 10.0.12.0/30 is directly connected
C 192.168.1.0/24 is directly connected
The letter:
C
means:
Connected
R1 knows about these networks because they are directly connected to R1.
But R1 does not yet know about:
10.0.23.0
192.168.3.0
Those networks are farther away.
We need a way for the routers to share this information.
14. What is EIGRP?
This is where EIGRP comes in.
EIGRP stands for:
Enhanced Interior Gateway Routing Protocol
The name sounds complicated, but the basic idea is simple.
Think of three delivery drivers.
R1 knows some roads.
R2 knows some roads.
R3 knows some roads.
They communicate with each other and share information about the roads they know.
EIGRP is basically a system that allows routers to share information about networks and routes.
So:
R1: "I know how to reach Network 1."
R2: "I know how to reach Network 1 and Network 3."
R3: "I know how to reach Network 3."
Now the routers have a bigger map.
15. Configure EIGRP on R1
On R1:
enable
configure terminal
Start EIGRP:
router eigrp 100
The number 100 is the EIGRP autonomous system number.
For this lab, all three routers will use:
100
Now tell EIGRP which networks R1 should advertise:
network 192.168.1.0 0.0.0.255
network 10.0.12.0 0.0.0.3
Then:
no auto-summary
Finally:
end
16. Configure EIGRP on R2
On R2:
enable
configure terminal
router eigrp 100
network 10.0.12.0 0.0.0.3
network 10.0.23.0 0.0.0.3
no auto-summary
end
R2 can now exchange routing information with R1 and eventually R3.
17. Configure EIGRP on R3
On R3:
enable
configure terminal
router eigrp 100
network 10.0.23.0 0.0.0.3
network 192.168.3.0 0.0.0.255
no auto-summary
end
Now all three routers are running EIGRP.
EIGRP
↓
R1 ←────────────→ R2 ←────────────→ R3
18. Check the EIGRP neighbors
On R1, run:
show ip eigrp neighbors
You should see R2 as a neighbor.
This means:
R1 and R2 have successfully discovered each other using EIGRP.
Think of it like two people exchanging phone numbers.
Before:
R1 ❌ R2
After EIGRP:
R1 🤝 R2
They can now exchange routing information.
19. Check the routing table again
On R1:
show ip route
Now you should see routes beginning with:
D
For example:
D 192.168.3.0/24
The letter D means:
This route was learned through EIGRP.
This is a big moment in the lab.
Before EIGRP:
R1:
192.168.1.0 ✅
10.0.12.0 ✅
192.168.3.0 ❌
After EIGRP:
R1:
192.168.1.0 ✅
10.0.12.0 ✅
192.168.3.0 ✅
R1 has learned how to reach the network behind R3.
20. Test communication again
Now try:
ping 10.0.23.2
This time it should work.
The path is:
R1 → R2 → R3
R1 learned from EIGRP that R2 can help it reach the network behind R3.
21. The big picture
Everything we did can be simplified to this:
EIGRP
↓
PC1 R1 R2 R3 PC3
| | | | |
| | | | |
192.168.1.0 ─────┘ | └──── 192.168.3.0
\______________|______________/
routing information
When PC1 wants to communicate with PC3:
PC1
↓
R1
↓
R2
↓
R3
↓
PC3
EIGRP helps the routers understand which direction to send the traffic.
22. What I learned from this lab
As a beginner, these are the concepts I would remember:
IP address
An IP address is like a device's address.
Example:
192.168.1.10
Router
A router is like a traffic director.
It decides where network traffic should go.
Routing table
A routing table is like a map.
It tells the router where different networks can be reached.
EIGRP
EIGRP allows routers to share route information.
ping
ping is a simple way to ask:
"Can I reach that device?"
show ip route
This lets us look at the router's map.
show ip eigrp neighbors
This lets us see which routers have established an EIGRP relationship.
23. Commands we learned
Here are the important commands from this lab:
enable
Enter privileged mode.
configure terminal
Enter configuration mode.
hostname R1
Give the router a name.
interface gigabitEthernet 0/0
Select a router interface.
ip address 192.168.1.1 255.255.255.0
Give the interface an IP address.
no shutdown
Turn the interface on.
show ip interface brief
Check interface status.
ping 10.0.12.2
Test connectivity.
show ip route
View the routing table.
router eigrp 100
Start EIGRP.
show ip eigrp neighbors
Check EIGRP neighbors.
24. What's next?
This was my first step into Cisco networking.
The next lab will be more interesting:
VLANs and Inter-VLAN Routing
We'll create something like:
Router
|
Switch
/ \
VLAN 10 VLAN 20
| |
Sales PC IT PC
We'll learn why companies separate departments into different networks and how a router allows those networks to communicate.
After that, we can continue toward:
VLANs
Inter-VLAN routing
DHCP
Static routing
EIGRP troubleshooting
OSPF
ACLs
NAT
Network security
AWS networking
The goal is not just to memorize Cisco commands.
The goal is to understand what the network is doing and why.
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