Convert decimal to binary and back — understand how subnet masks work in binary
2
Design a VLSM addressing plan — fit 4 subnets of different sizes into 192.168.1.0/24
3
Configure R1 interfaces with the correct IPs and masks from your VLSM plan
4
Verify the routing table — all 4 subnets must appear as connected routes
5
Ping across subnets to confirm end-to-end reachability
6
Troubleshoot a wrong-mask fault — diagnose why one subnet is overlapping
7
Knowledge check — binary, subnetting and VLSM mastery
VLSM Requirements — fit all 4 into 192.168.1.0/24
Subnet
Hosts needed
Interface
Suggested allocation
Sales LAN
60 hosts
Gi0/0
192.168.1.0/26 (62 usable)
Engineering LAN
28 hosts
Gi0/1
192.168.1.64/27 (30 usable)
Management LAN
12 hosts
Gi0/2
192.168.1.96/28 (14 usable)
WAN Link
2 hosts
Gi0/3
192.168.1.112/30 (2 usable)
Key Concepts
Concept
What it means
VLSM
Variable Length Subnet Masking — using different prefix lengths for different subnets to avoid wasting IP addresses.
Subnet mask
Defines which bits are the network portion. /26 = 26 network bits = 255.255.255.192. The remaining 6 bits = 2⁶−2 = 62 hosts.
Usable hosts
2^(host bits) − 2. Subtract 2 for network address (all 0s) and broadcast (all 1s).
Subnet ID
The lowest address in the block (host bits all 0s). Not assignable to a device.
Broadcast
The highest address in the block (host bits all 1s). Not assignable to a device.
Supported Commands — R1
Command
Purpose
enable
Enter privileged EXEC mode
configure terminal
Enter global configuration mode
interface Gi0/0–3
Enter interface config (Gi0/0, Gi0/1, Gi0/2, Gi0/3)
ip address <addr> <mask>
Assign IP and subnet mask to interface
no shutdown
Bring interface up
show ip interface brief
Verify all interface IPs and state
show ip route
Confirm all 4 subnets are in the routing table
ping <ip>
Test reachability across subnets
show running-config
View full device configuration
🧮 After configuring Gi0/0, the Subnet Calculator button appears in the top bar — use it for binary conversion, VLSM design reference, and mask lookup.
The IP addresses in the table above are suggested. As long as each interface uses the correct prefix length and a valid host address from that subnet, the lab will accept it.
🧮 Subnet Calculator
Binary converter · VLSM design · Mask reference
Enter a decimal number (0–255) to see its binary representation, or enter binary to convert to decimal.
Decimal
⇄
Binary (8 bits)
Bit breakdown
192 = 128 + 64 = 11000000
Common subnet mask octets in binary
/24 → .0
00000000
/25 → .128
10000000
/26 → .192
11000000
/27 → .224
11100000
/28 → .240
11110000
/29 → .248
11111000
/30 → .252
11111100
/32 → .255
11111111
VLSM allocates subnets largest-first to avoid gaps. Here is the complete plan for this lab's 192.168.1.0/24 address block.
Subnet
Network
Mask
Usable Range
Broadcast
Hosts
Sales (Gi0/0)
192.168.1.0
/26
192.168.1.1 – .62
192.168.1.63
62
Engineering (Gi0/1)
192.168.1.64
/27
192.168.1.65 – .94
192.168.1.95
30
Management (Gi0/2)
192.168.1.96
/28
192.168.1.97 – .110
192.168.1.111
14
WAN Link (Gi0/3)
192.168.1.112
/30
192.168.1.113 – .114
192.168.1.115
2
Address space visualisation — 192.168.1.0/24 (256 addresses)
/26 Sales
/27 Eng
/28 Mgmt
/30
Unused
How VLSM works: Sort subnets by hosts needed, largest first. Allocate the smallest possible prefix that fits. Move the start address forward by the block size after each allocation. Never overlap.