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Lesson 1 of 5

Why Network Automation

Lab Objectives

  • Understand the business case for network automation: speed, consistency, and reduced human error.
  • Perform a small, manual network configuration using the provided topology to illustrate the problems automation solves.
  • Verify configuration and observe how manual tasks scale (and why they become error-prone).

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 Router Interfaces

Assign IP addresses to the router interfaces in the base topology so each neighbor link is reachable. Use the Gi0/0–Gi0/2 interface names on R1 and the Gi0/0/Gi0/1 names on R2 and the Gi0/0 name on R4. For R3, assign the matching 10.10.20.x address to its Gi0/0 interface.

Parameters:

  • R1: Gi0/0 = 10.10.10.1/24, Gi0/1 = 10.10.20.1/24, Gi0/2 = 10.10.30.1/24
  • R2: Gi0/0 = 10.10.10.2/24, Gi0/1 = 10.10.40.1/24
  • R3: Gi0/0 = 10.10.20.2/24
  • R4: Gi0/0 = 10.10.30.2/24

Task 2: Configure Default Routes (Manual)

On each branch router (R2, R3, R4) configure a static default route that points to R1 so they can reach the simulated Internet. On R1 configure a default route that points to the Internet gateway 203.0.113.1.

Parameters:

  • On R2: default via 10.10.10.1
  • On R3: default via 10.10.20.1
  • On R4: default via 10.10.30.1
  • On R1: default via 203.0.113.1

Task 3: Create VLANs on S1 and SVI IPs

On S1 create three VLANs and configure SVI addresses to represent the three internal networks. Use these addresses for the switch virtual interfaces (SVIs):

  • VLAN 10 — 192.168.1.1/24 (Sales)
  • VLAN 20 — 192.168.2.1/24 (Engineering)
  • VLAN 30 — 192.168.3.1/24 (Management)

Think About It: If you had 200 switches and 2,000 VLANs to configure across a campus, why would doing Task 3 manually be a problem? What kinds of errors would you expect humans to make, and how could automation help?

Lab Solution

Task 1 Solution: Configure Router Interfaces

What we are doing: Assign interface IPs so each point-to-point link is in the correct subnet; this establishes layer-3 adjacency so routers can exchange traffic and forward packets.

! R1 configuration
configure terminal
interface GigabitEthernet0/0
 ip address 10.10.10.1 255.255.255.0
 no shutdown
exit
interface GigabitEthernet0/1
 ip address 10.10.20.1 255.255.255.0
 no shutdown
exit
interface GigabitEthernet0/2
 ip address 10.10.30.1 255.255.255.0
 no shutdown
exit
end

What the commands do and why they matter:

  • interface GigabitEthernet0/0 — selects the physical interface; you must be in interface configuration mode to set addresses.
  • ip address 10.10.10.1 255.255.255.0 — assigns the IP and mask for the link. Without a correct IP, the neighbor cannot be reached.
  • no shutdown — ensures the interface is administratively up. Many connectivity problems are simply caused by interfaces being shut down.

Verification:

R1#show ip interface brief
Interface              IP-Address      OK? Method Status                Protocol
GigabitEthernet0/0     10.10.10.1      YES manual up                    up
GigabitEthernet0/1     10.10.20.1      YES manual up                    up
GigabitEthernet0/2     10.10.30.1      YES manual up                    up

Repeat on R2, R3, R4:

! R2 configuration
configure terminal
interface GigabitEthernet0/0
 ip address 10.10.10.2 255.255.255.0
 no shutdown
exit
interface GigabitEthernet0/1
 ip address 10.10.40.1 255.255.255.0
 no shutdown
exit
end

Verification:

R2#show ip interface brief
Interface              IP-Address      OK? Method Status                Protocol
GigabitEthernet0/0     10.10.10.2      YES manual up                    up
GigabitEthernet0/1     10.10.40.1      YES manual up                    up

! R3 configuration
configure terminal
interface GigabitEthernet0/0
 ip address 10.10.20.2 255.255.255.0
 no shutdown
exit
end

Verification:

R3#show ip interface brief
Interface              IP-Address      OK? Method Status                Protocol
GigabitEthernet0/0     10.10.20.2      YES manual up                    up

! R4 configuration
configure terminal
interface GigabitEthernet0/0
 ip address 10.10.30.2 255.255.255.0
 no shutdown
exit
end

Verification:

R4#show ip interface brief
Interface              IP-Address      OK? Method Status                Protocol
GigabitEthernet0/0     10.10.30.2      YES manual up                    up


<div class="topology-diagram">
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</div>

cisco
! On R2
configure terminal
ip route 0.0.0.0 0.0.0.0 10.10.10.1
end

What this does and why it matters:

  • ip route 0.0.0.0 0.0.0.0 10.10.10.1 — creates a default route (catch-all). Branch routers usually use the hub/router as the default path to external networks. This is how hosts behind R2 will reach networks they do not know about.

Verification:

R2#show ip route
Codes: C - connected, S - static, * - candidate default
S*    0.0.0.0/0 [1/0] via 10.10.10.1
C     10.10.10.0/24 is directly connected, GigabitEthernet0/0
C     10.10.40.0/24 is directly connected, GigabitEthernet0/1

! On R3
configure terminal
ip route 0.0.0.0 0.0.0.0 10.10.20.1
end

Verification:

R3#show ip route
S*    0.0.0.0/0 [1/0] via 10.10.20.1
C     10.10.20.0/24 is directly connected, GigabitEthernet0/0

! On R4
configure terminal
ip route 0.0.0.0 0.0.0.0 10.10.30.1
end

Verification:

R4#show ip route
S*    0.0.0.0/0 [1/0] via 10.10.30.1
C     10.10.30.0/24 is directly connected, GigabitEthernet0/0

! On R1 - point unknown traffic to the simulated Internet gateway
configure terminal
ip route 0.0.0.0 0.0.0.0 203.0.113.1
end

Verification:

R1#show ip route
S*    0.0.0.0/0 [1/0] via 203.0.113.1
C     10.10.10.0/24 is directly connected, GigabitEthernet0/0
C     10.10.20.0/24 is directly connected, GigabitEthernet0/1
C     10.10.30.0/24 is directly connected, GigabitEthernet0/2


<div class="topology-diagram">
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</div>

cisco
! On S1
configure terminal
vlan 10
 name Sales
exit
vlan 20
 name Engineering
exit
vlan 30
 name Management
exit

interface Vlan10
 ip address 192.168.1.1 255.255.255.0
 no shutdown
exit

interface Vlan20
 ip address 192.168.2.1 255.255.255.0
 no shutdown
exit

interface Vlan30
 ip address 192.168.3.1 255.255.255.0
 no shutdown
exit
end

What this does and why it matters:

  • vlan <id> creates the VLAN in the VLAN database — without this, trunked ports cannot carry that VLAN.
  • interface VlanX and ip address assign the SVI address used as the default gateway for hosts in that VLAN. Without an SVI, hosts need an external router-on-a-stick to reach other subnets.

Verification:

S1#show ip interface brief
Interface              IP-Address      OK? Method Status                Protocol
Vlan10                 192.168.1.1     YES manual up                    up
Vlan20                 192.168.2.1     YES manual up                    up
Vlan30                 192.168.3.1     YES manual up                    up


<div class="topology-diagram">
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</div>

cisco
R2#configure terminal
R2(config)#no ip route 0.0.0.0 0.0.0.0 10.10.20.1
R2(config)#ip route 0.0.0.0 0.0.0.0 10.10.10.1
R2(config)#end

Explanation: R2's correct upstream neighbor is R1 at 10.10.10.1 on Gi0/0. Pointing the default to the wrong router makes the traffic black-hole.

Verification Checklist

  • All router interfaces show the correct IP and status (use show ip interface brief).
  • Each branch router (R2/R3/R4) has a default route pointing to R1 (show ip route).
  • S1 has VLANs 10/20/30 created and SVIs configured with the correct IPs (show ip interface brief on S1).

Common Mistakes

SymptomCauseFix
Default route missing on R3Forgot to configure ip route 0.0.0.0 0.0.0.0 10.10.20.1Add the static default route pointing to R1
Interface shows administratively downno shutdown not appliedEnter interface mode and run no shutdown
VLAN exists but SVI is downVLAN not created or no active ports in VLANCreate VLAN with vlan <id> and ensure at least one access/trunk port is up, then enable the SVI

Challenge Task

Without step-by-step guidance, design a simple automation plan (describe tools, templates, and verification commands) that would automate Tasks 1–3 for 50 branch sites. Consider idempotency (re-running should not cause errors), templating for IP assignments, and verification steps to prove success.

Important insight: Automation doesn’t remove the need to understand the network — it amplifies human intent. Learn the manual steps first (this lab) so your automation templates apply the correct intent consistently and safely.

Key takeaway: Manual configuration is essential to learn fundamentals, but automation scales those fundamentals across hundreds or thousands of devices with consistent, repeatable results — reducing time to deploy and the chance of human error.

Practice with Hands-On Labs

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