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Lesson 5 of 5

Configuration Fundamentals Challenge

Lab Objectives

  • Configure router hostnames and physical interfaces with the exact IP addresses from the base topology.
  • Add static default routes on edge routers so all routers can forward to the central gateway.
  • Verify basic IPv4 connectivity between routers using show and ping commands.

Lab Tasks (Try It Yourself First!)

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

ASCII topology (use this exact topology and IPs):

                    [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

Task 1: Configure Router Hostnames and Interfaces

Configure R1, R2, R3 and R4 hostnames and the Gi0/0–Gi0/2 interface IPs exactly as shown in the topology. Enable interfaces (no shutdown).

Task 2: Configure Default Routes on R2, R3, R4

On R2, R3 and R4 configure a static default route (0.0.0.0/0) pointing to R1’s address on the shared link (next-hop toward R1).

Task 3: Verify Router Connectivity

From each router:

  • Confirm interfaces are up and have the configured IPs.
  • Verify you can ping R1 from R2, R3 and R4.
  • Show the routing table to confirm the default route is present.

Think About It: Why do we configure a default route on R2/R3/R4 to point to R1 rather than adding individual routes to every remote network? When would you prefer a routing protocol instead?

Lab Solution

Task 1 Solution: Configure Router Hostnames and Interfaces

What we are doing: We assign meaningful hostnames and configure the physical GigabitEthernet interfaces with the IP addresses defined in the topology. This creates the L2/L3 adjacency required for inter-router IP reachability. In production, naming devices and setting correct interface IPs is the first step before adding services or routing.

R1(config)# hostname R1
R1(config)# interface GigabitEthernet0/0
R1(config-if)# ip address 10.10.10.1 255.255.255.0
R1(config-if)# no shutdown
R1(config-if)# exit
R1(config)# interface GigabitEthernet0/1
R1(config-if)# ip address 10.10.20.1 255.255.255.0
R1(config-if)# no shutdown
R1(config-if)# exit
R1(config)# interface GigabitEthernet0/2
R1(config-if)# ip address 10.10.30.1 255.255.255.0
R1(config-if)# no shutdown

What just happened:

  • hostname R1 — sets the device prompt; meaningful names make troubleshooting and monitoring easier.
  • interface GigabitEthernet0/x — enters interface configuration mode for the physical link.
  • ip address A.B.C.D 255.255.255.0 — assigns the IPv4 address and mask.
  • no shutdown — administratively enables the interface so the link can pass traffic.

Verify:

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 the same pattern on R2, R3 and R4 using these commands (replace hostname and IPs exactly):

R2:

R2(config)# hostname R2
R2(config)# interface GigabitEthernet0/0
R2(config-if)# ip address 10.10.10.2 255.255.255.0
R2(config-if)# no shutdown
R2(config-if)# exit
R2(config)# interface GigabitEthernet0/1
R2(config-if)# ip address 10.10.40.1 255.255.255.0
R2(config-if)# no shutdown

Verify:

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:

R3(config)# hostname R3
R3(config)# interface GigabitEthernet0/0
R3(config-if)# ip address 10.10.20.2 255.255.255.0
R3(config-if)# no shutdown

Verify:

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

R4:

R4(config)# hostname R4
R4(config)# interface GigabitEthernet0/0
R4(config-if)# ip address 10.10.30.2 255.255.255.0
R4(config-if)# no shutdown

Verify:

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

Tip: Think of each interface IP like a mailbox address on a street: if the boxes (IP addresses) are wrong or closed (shutdown), mail (packets) cannot be delivered.

Task 2 Solution: Configure Default Routes on R2, R3, R4

What we are doing: We configure a single default route on each spoke router (R2, R3, R4) pointing toward R1. This tells the router “send everything you don’t know to R1.” This is common in small topologies or where a central edge router handles Internet or inter-site traffic.

R2:

R2(config)# ip route 0.0.0.0 0.0.0.0 10.10.10.1

What it does: Creates a static default route; any packet without a more specific route will be sent to 10.10.10.1 (R1).

Verify:

R2# show ip route
Codes: C - connected, S - static, ... 
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

R3:

R3(config)# ip route 0.0.0.0 0.0.0.0 10.10.20.1

Verify:

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

R4:

R4(config)# ip route 0.0.0.0 0.0.0.0 10.10.30.1

Verify:

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

Real-world context: Small branch offices often use a default route to the hub router to avoid maintaining many individual routes. In larger networks you would use a dynamic routing protocol instead.

Task 3 Solution: Verify Router Connectivity

What we are doing: Use ping and show commands to confirm the network is reachable and the default routes are installed.

From R2, ping R1:

R2# ping 10.10.10.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.10.10.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/1/2 ms

From R3, ping R1:

R3# ping 10.10.20.1
.....
Success rate is 100 percent (5/5)

From R4, ping R1:

R4# ping 10.10.30.1
.....
Success rate is 100 percent (5/5)

Also verify R1’s routing table shows the connected networks and can forward traffic to spokes (if static routes to other subnets added later):

R1# show ip route
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

Troubleshooting Scenario

Scenario: R2 cannot ping R1

Symptom: R2# ping 10.10.10.1 shows all dots (no replies). Your task: Find and fix the issue.

Hint: Check the interface status and IP configuration on both ends.

Solution:

  1. On R2 run:
R2# show ip interface brief

If GigabitEthernet0/0 is administratively down or has wrong IP (e.g., 10.10.10.3), fix:

  1. Correct commands:
R2(config)# interface GigabitEthernet0/0
R2(config-if)# ip address 10.10.10.2 255.255.255.0
R2(config-if)# no shutdown
  1. Verify with:
R2# ping 10.10.10.1

Explanation: A common mistake is a typo in the IP or forgot no shutdown. Interfaces must be up/up and IPs must be in the same subnet to establish link-layer and IP connectivity.

Verification Checklist

  • Each router hostname is set to R1, R2, R3, R4.
  • IP addresses configured on GigabitEthernet interfaces per topology.
  • Interfaces are administratively up and operational (Status = up, Protocol = up).
  • Default route exists on R2, R3, R4 pointing to the appropriate R1 interface.
  • R2/R3/R4 can ping R1 successfully.

Common Mistakes

SymptomCauseFix
Ping to R1 times outInterface is shutdown (administratively down)Enter interface and run no shutdown
Ping to neighbor failsWrong IP address or mask (typo)Reconfigure ip address to the correct value
Default route not visibleip route not configured, or wrong next-hop IPAdd ip route 0.0.0.0 0.0.0.0 <R1-IP> with correct next-hop
Interface shows up/downPhysical/link mismatch or cable issueCheck cables, check remote interface, ensure both ends are up

Warning: Small typos in IPs or using the wrong interface name (Gig0/0 vs Gi0/0) are frequent mistakes for beginners. Use ? to discover exact interface names and show run to review config.

Challenge Task

Without step-by-step guidance, configure R1 to reach the simulated Internet IP 203.0.113.1 by adding an additional interface (or loopback) and add a static route on each spoke so that they can reach 203.0.113.1 through R1. Verify end-to-end reachability from R2 to 203.0.113.1.

This challenge practices extending the hub-and-spoke default route logic to reach an external network and tests your use of ip route and verification commands independently.

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