Same for: 37.4.9 Lab - Verify Address With a Subnet Calculator
1.4.9 Lab - Verify Address with a Subnet Calculator
Objectives
Subnet calculators can be helpful in providing information about a specific network or subnet. Typically, a subnet calculator will ask for a specific IPv4 or IPv6 address along with its subnet mask or prefix length. It will then calculate the address ranges for the full range of subnetworks specified.
In this activity, you will determine the IPv4 address and subnet mask of your device and use an online subnet calculator to determine the IPv4 network address.
Instructions
Part 1: Determine Your Device’s IPv4 Address and Subnet Mask
Depending on your device’s operating system (computer or mobile phone), use the proper command to determine the following:
- IPv4 address
- Subnet mask
Record IPv4 address and subnet mask for your device.
Answer: The exact values will vary depending on your device and network. Use the command or menu that matches your operating system:
- Windows: Open Command Prompt and enter
ipconfig. Find the adapter you are currently using (Wi-Fi or Ethernet) and look for the IPv4 Address and Subnet Mask lines. - Linux: Open a terminal and enter
ip -4 addr show. The address is displayed in prefix notation (for example,192.168.1.105/24), where/24is equal to the subnet mask255.255.255.0. - macOS: Open Terminal and enter
ipconfig getifaddr en0to display the IPv4 address, thenipconfig getoption en0 subnet_maskto display the subnet mask. On some Macs, the active interface may been1instead ofen0. - iOS: Go to Settings > Wi-Fi and tap the (i) icon next to the connected network.
- Android: Go to Settings > Network & internet > Wi-Fi and tap the connected network. The menu names may differ slightly depending on the device manufacturer.
Example output (Windows):
C:\> ipconfig Wireless LAN adapter Wi-Fi: Connection-specific DNS Suffix . : IPv4 Address. . . . . . . . . . . : 192.168.1.105 Subnet Mask . . . . . . . . . . . : 255.255.255.0 Default Gateway . . . . . . . . . : 192.168.1.1
Based on this example, record the following information:
- IPv4 address: 192.168.1.105
- Subnet mask: 255.255.255.0 (/24)
Tip: Also write down the Default Gateway address. You will use it in Part 4 to verify that your device and its default gateway are on the same network.
Part 2: Search for an Online Subnet Calculator
a. Using your web browser, search for IP subnet calculator to get a list of various IP subnet calculators.
b. Choose an IP subnet calculator from the web search results.
Answer: You can use any IP subnet calculator from the search results. For the quickest way to complete this lab, use our free Subnet & Wildcard Mask Calculator. It is ad-light, works on both computers and mobile phones, and does not require registration.
Compared with most online subnet calculators, this tool shows you more than the final result:
- Complete subnet details: network address, range of host addresses, broadcast address, and number of usable hosts. These are the exact values required in Part 4 of this lab.
- Binary breakdown: each value is displayed in binary, so you can see how the subnet mask separates the network portion from the host portion.
- Step-by-step calculation: the tool explains how each result is calculated, which helps you practice subnetting for the CCNA exam instead of only copying the answer.
- Wildcard mask: useful later when you configure ACLs and OSPF on Cisco routers.
How to use it:
- Open the Subnet & Wildcard Mask Calculator.
- In the IP Address field, enter the IPv4 address you recorded in Part 1 (for example,
192.168.1.105). - In the Subnet Mask / CIDR drop-down list, select the matching subnet mask (for example,
/24 — 255.255.255.0). - Click Calculate and review the results in the Subnet Details table.
Tip: The calculator opens in a new tab, so you can keep this lab page open and switch back to record your answers in Part 4.
Part 3: Enter the IPv4 Address and Subnet Mask
In the appropriate area, enter your device’s IPv4 address and subnet mask. Perform the calculation to determine the IPv4 network address.
Using the example from Part 1, enter 192.168.1.105 and select /24, then click Calculate.
Part 4: Examine the IPv4 Network Address
The actual information provided will vary but the most common information includes:
- Network address
- Range of host addresses
- Broadcast address
- Number of usable hosts
The IPv4 network address displayed is the network address of your device. If the output includes a range of host addresses, the address of your device should be within that range.
This information can be useful in verifying:
- If the device in question is on the same network as its default gateway.
- If two devices are on different networks, and therefore, proper routing must be utilized for reachability.
Note: Many of these subnet calculators will also give the address class; Class A, B or C. It is important to note that this information is no longer relevant. Classful addressing was discontinued with the introduction of Classless Inter-Domain Routing (CIDR) in 1993.
Using the information from the results, answer the following questions:
Note: The answers below are based on the example used in this lab (IPv4 address 192.168.1.105 with subnet mask 255.255.255.0 or /24). Your own results will be different if your device has a different IPv4 address or subnet mask.
What is your network address?
Answer: 192.168.1.0 (written as 192.168.1.0/24 in CIDR notation)
Explanation: The subnet mask /24 means the first 24 bits (the first three octets) are the network portion, and the last 8 bits are the host portion. The network address is found by setting all host bits to 0:
IP address: 11000000.10101000.00000001.01101001 (192.168.1.105) Subnet mask: 11111111.11111111.11111111.00000000 (255.255.255.0) Network address: 11000000.10101000.00000001.00000000 (192.168.1.0)
What is the range of host addresses?
Answer: 192.168.1.1 – 192.168.1.254
Explanation: The first address in the subnet (.0) is reserved as the network address, and the last address (.255) is reserved as the broadcast address. All addresses in between can be assigned to hosts. The example device address 192.168.1.105 is within this range, as expected.
What is the broadcast address?
Answer: 192.168.1.255
Explanation: The broadcast address is found by setting all host bits to 1 (11000000.10101000.00000001.11111111). A packet sent to this address is delivered to every host in the 192.168.1.0/24 network.
What is the number of usable hosts?
Answer: 254
Explanation: A /24 subnet has 8 host bits, which gives 28 = 256 total addresses. Subtract 2 reserved addresses (the network address and the broadcast address): 256 − 2 = 254 usable host addresses.
Quick formula: Usable hosts = 2n − 2, where n is the number of host bits (32 − prefix length).
Verification: In this example, the default gateway 192.168.1.1 is also within the host range 192.168.1.1 – 192.168.1.254. This confirms that the device and its default gateway are on the same network, so the device can send traffic to other networks through the gateway. If the default gateway were outside this range, the device would not be able to reach remote networks.
Note about “IP Class”: The calculator also shows that 192.168.1.105 is a Class C address. As mentioned in this lab, this information is for reference only. Classful addressing is no longer used; modern networks use CIDR, where the prefix length (such as /24) defines the network portion, not the address class.
