NHPREP — Hands-On CCNA, CCNP, CCIE Labs & Networking Courses

Lab Objectives

Learn how to calculate the network address, broadcast address, and first/last usable host for any IPv4 address + mask.
Apply those calculations to subnets used in the base topology and verify router interface configuration.
Practice configuring router interfaces and a Loopback to represent a VLAN gateway so you can verify your calculations with IOS commands.

ASCII Topology (BASE LAB TOPOLOGY — exact IPs shown)

                    [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

IP Scheme (exact)

10.10.10.0/24 — R1-R2 link
10.10.20.0/24 — R1-R3 link
10.10.30.0/24 — R1-R4 link
10.10.40.0/24 — R2-S1 link
192.168.1.0/24 — VLAN 10 (Sales)
192.168.2.0/24 — VLAN 20 (Engineering)
192.168.3.0/24 — VLAN 30 (Management)
203.0.113.0/24 — Public/Internet simulation

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 Interface IP addresses

Assign the exact IP addresses to R1, R2, R3 and R4 interfaces shown in the topology:

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 Do not change other parameters.

Task 2: Calculate subnet details (network, broadcast, usable hosts)

For each of these example host IPs and masks, calculate:

Network address
Broadcast address
First usable host
Last usable host Use manual calculation or binary method (no IOS commands). a) 192.168.1.57/26
b) 192.168.2.130/25
c) 192.168.3.5/29

Task 3: Configure a Loopback to represent VLAN 10 gateway and verify

Create Loopback0 on R2 and assign 192.168.1.1/24 (represents the VLAN 10 gateway). Verify the IP is present and reachable from R1 by displaying interface and route information.

Think About It: If VLAN 10 uses the /26 subnets in Task 2a, why would you choose /26 instead of /24 for a departmental VLAN in a real network? Consider address waste and broadcast domain size.

Lab Solution

Task 1 Solution: Configure Router Interface IP addresses

What we are doing: Setting the exact IPv4 addresses on router physical interfaces to match the lab topology so devices share the right L2/L3 networks. This is necessary because correct addressing ensures adjacency and reachability between routers and downstream networks.

! On R1
interface GigabitEthernet0/0
 ip address 10.10.10.1 255.255.255.0
 no shutdown
!
interface GigabitEthernet0/1
 ip address 10.10.20.1 255.255.255.0
 no shutdown
!
interface GigabitEthernet0/2
 ip address 10.10.30.1 255.255.255.0
 no shutdown

! On R2
interface GigabitEthernet0/0
 ip address 10.10.10.2 255.255.255.0
 no shutdown
!
interface GigabitEthernet0/1
 ip address 10.10.40.1 255.255.255.0
 no shutdown

! On R3
interface GigabitEthernet0/0
 ip address 10.10.20.2 255.255.255.0
 no shutdown

! On R4
interface GigabitEthernet0/0
 ip address 10.10.30.2 255.255.255.0
 no shutdown

What just happened:

Each interface command selects the physical interface.
ip address x.x.x.x 255.255.255.0 assigns the IPv4 address and mask (here /24).
no shutdown enables the interface so it can form adjacency and pass traffic. These steps matter because wrong IP or mask means devices will be on different networks and cannot communicate directly.

Verify:

show ip interface brief

Expected output excerpt (full lines shown for lab interfaces):

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
Loopback0              unassigned      YES manual administratively down down

(Repeat show ip interface brief on R2/R3/R4 to confirm their configured addresses.)

Tip: On a simulator/emulator physical link state may show "up up" only if both ends are configured. If the far side is missing, you'll see "up/down" — this is a clue to check the neighbor.

Task 2 Solution: Calculate subnet details

What we are doing: For each IP and prefix, we manually derive the network ID, broadcast, and usable host range. Understanding binary division of the host portion is essential — think of the mask as a divider that partitions the 32-bit address into network and host bits.

a) 192.168.1.57/26

/26 = 255.255.255.192 => block size in last octet = 256 - 192 = 64
Subnet blocks: 0, 64, 128...
57 lies in the 0–63 block.
Network = 192.168.1.0
Broadcast = 192.168.1.63
First usable = 192.168.1.1
Last usable = 192.168.1.62

b) 192.168.2.130/25

/25 = 255.255.255.128 => block size = 128
Blocks: 0–127, 128–255
130 lies in 128–255 block.
Network = 192.168.2.128
Broadcast = 192.168.2.255
First usable = 192.168.2.129
Last usable = 192.168.2.254

c) 192.168.3.5/29

/29 = 255.255.255.248 => block size = 8
Blocks: 0–7, 8–15, ...
5 lies in 0–7 block.
Network = 192.168.3.0
Broadcast = 192.168.3.7
First usable = 192.168.3.1
Last usable = 192.168.3.6

Why this matters in production: Choosing /26 instead of /24 lets you split a /24 into four smaller VLAN networks. That reduces broadcast domain size and preserves address space when you only need ~60 hosts per VLAN. Conversely, picking too-small a mask wastes administrative effort and can complicate routing.

Task 3 Solution: Configure Loopback0 on R2 as VLAN 10 gateway and verify

What we are doing: Create a Loopback on R2 with 192.168.1.1/24 to represent the VLAN 10 gateway. Loopbacks are logical interfaces always up/up and are useful for stable gateway addresses and testing.

! On R2
interface Loopback0
 ip address 192.168.1.1 255.255.255.0
!
end

What just happened:

interface Loopback0 creates a stable virtual interface.
ip address assigns the VLAN gateway address. Using a Loopback ensures the address won't go down with a physical link failure and is ideal for testing and routing protocols.

Verify:

show ip interface brief

Expected relevant output on R2:

Interface              IP-Address      OK? Method Status                Protocol
Loopback0              192.168.1.1     YES manual up                    up
GigabitEthernet0/0     10.10.10.2      YES manual up                    up
GigabitEthernet0/1     10.10.40.1      YES manual up                    up

To verify reachability from R1 (assuming connectivity on the 10.10.10.0/24 link):

! From R1
ping 192.168.1.1

Expected ping success (sample):

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.1.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/5/10 ms

Troubleshooting Scenario

Scenario: R1 cannot ping 192.168.1.1

Symptom: Ping from R1 to 192.168.1.1 fails.

Your task: Find and fix the issue.

Hint: Check both addressing and mask on R2 Loopback and the R1-R2 link status.

Solution:

Verify R2 Loopback address with show ip interface brief. If Loopback is unassigned or has wrong mask, correct it:

interface Loopback0
 ip address 192.168.1.1 255.255.255.0

Verify R1 and R2 Gi0/0 are in same /24 and up:

show ip interface brief

If link down, ensure no shutdown on both ends and physical connectivity in emulator.

Verification Checklist

R1 interfaces configured with 10.10.10.1/24, 10.10.20.1/24, 10.10.30.1/24
R2 configured with 10.10.10.2/24 and Loopback0 192.168.1.1/24
Manual subnet calculations for /26, /25, /29 match the answers above
R1 can ping R2 Loopback0

Common Mistakes

Symptom	Cause	Fix
Ping to Loopback fails	Loopback mask mistaken (e.g., /26 vs /24)	Reconfigure Loopback with correct mask `ip address 192.168.1.1 255.255.255.0`
Interfaces show up/down	One side of link not configured or shutdown	`no shutdown` on both interfaces; check neighbor IPs
Wrong subnet calculation	Incorrect block size or not converting mask to decimal	Recompute: block = 256 - mask_octet; find containing block

Important: Think of subnetting like dividing a cake — the mask decides the slice size. If you pick a slice (subnet) too big, you waste cake; pick too small and you may not feed everyone.

Challenge Task

Divide 192.168.1.0/24 into 8 equal subnets. For the subnet that contains host 192.168.1.210, identify network, broadcast, and usable host range. Then assign that gateway address as Loopback1 on R3 and verify end-to-end reachability from R4. (No step-by-step provided.)

Calculating Subnets