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Applicable Model(s)
MapleLink
MapleLink-Lite
Title
How to subnet
Date
04/24/2025
Rev
00
P/N
TN3002
Summary
Subnetting is the practice of dividing a large IP network into smaller, more manageable subnetworks. Each subnet functions as its own small network while still being part of the larger whole. This allows for better organization and segmentation of devices within a network. Subnetting helps conserve IP addresses and provides greater control over traffic flow between devices.
Note: Subnetting improves network performance, enhances security and broadcast containment, as well as simplifies management and reduces congestion.
Solution
Key Terms Defined
- IP Address: A unique ID assigned to each device on a network.
- Example: 192.168.1.10
- Subnet Mask: A 32-bit number that determines the network and host portions of an IP address.
- Example: 255.255.255.0
- Network Portion: The network portion IDs the subnet
- Example: 192.168.1.0/24, network portion is 192.168.1 with a network address of 192.168.1.0
- Host Portions: The host portion IDs devices within that subnet, and assignable IPs to devices.
- Example: 192.168.1.0/24, host portion is 192.168.1.1 to 192.168.1.254
- CIDR Notation: Classless Inter-Domain Routing notation (e.g., /24) defines how many bits are used for the network portion.
- Broadcast Address: The last IP in a subnet, used to send data to all devices in that subnet.
- Example: 192.168.1.0/24, broadcast IP is 192.168.1.255
- Boundary IP: First and Last IP addresses with a subnet. First being Network address, last being a Broadcast Address. These addresses cannot be assigned to individual devices within a network.
How subnetting works
Note: Network address is always the lowest in the block. Broadcast address is always the highest in the block. /8, /16, /24 CIDRs require starting at .0 boundary.
Let’s start with a Class C IP range: 192.168.1.0/24. This gives 256 addresses, including network and broadcast. We can break this into smaller subnets like:
- /25 —> 2 subnets with 128 addresses each
- /26 —> 4 subnets with 6 addresses each
- /27 —> 8 subnets with 32 addresses each
Visual aid
Understanding Subnet Boundaries Using CIDR
When working with IP addresses, CIDR (Classless Inter-Domain Routing) notation defines the size of a subnet, not the starting address. CIDR helps you determine how many IP addresses are available in a subnet and where subnet boundaries occur. You can use an online subnet calculator to simplify these calculations: https://www.calculator.net/ip-subnet-calculator.html
- Know the CIDR Value
- CIDR notation uses a slash followed by a number (e.g., /28), which tells you how many bits are used for the network portion of the address.
- CIDR notation uses a slash followed by a number (e.g., /28), which tells you how many bits are used for the network portion of the address.
- Calculate Subnet mask using CIDR
- CIDR = Subnet Mask
- /28 = 255.255.255.240
- /18 = 255.255.192.0
- CIDR = Subnet Mask
- Calculate Number of IP Addresses
- To find how many total IPs a subnet provides, subtract the CIDR value from 32 and raise 2 to that power:
– /28: 32 – 28 = 4 → 2⁴ = 16 IPs
– /18: 32 – 18 = 14 → 2¹⁴ = 16,384 IPs
Note: Two addresses in each subnet are reserved for the network ID and the broadcast address, so the number of usable IPs is always 2 less than the total.
- To find how many total IPs a subnet provides, subtract the CIDR value from 32 and raise 2 to that power:
- Understand Where Subnetting Happens
- CIDR Range —> Affected Octet
- /25 – /32 —> 4th octet
- /17 – /24 —> 3rd octet
- /9 – /16 —> 2nd octet
- /1 – /8 —> 1st octet
- CIDR Range —> Affected Octet
- Determine Subnet Boundaries
- To calculate subnet boundaries, subtract the subnet mask value from 256 and increment by that amount.
- Example: /28
- Subnet mask for 4th octet = 240
- 256 – 240 = 16
- Subnet boundaries: .0, .16, .32, .48, …, .240
- Example: /28
- To calculate subnet boundaries, subtract the subnet mask value from 256 and increment by that amount.
CIDR to subnet mask conversion table
Note: /0, /1, /32, /31 subnets are rare, and are used for special networking applications.