Introduction
IPv4 addressing identifies devices and networks so packets can be delivered. Understanding IPv4 structure, address types, and subnetting is essential for building and troubleshooting networks.
IPv4 Address Structure
An IPv4 address is 32 bits long and is usually written in dotted decimal format.
Example:
192.168.10.25
Each decimal number represents 8 bits, called an octet. Therefore, an IPv4 address has four octets.
192 .168 .10 .25
11000000 .10101000 .00001010 .00011001
A subnet mask or prefix length identifies which part of the address is the network portion and which part is the host portion.
Network, Host, and Broadcast Addresses
Each IPv4 network includes special addresses.
| Address Type | Description |
|---|---|
| Network address | Identifies the network itself. Host bits are all 0. |
| Host address | Assigned to an individual device. |
| Broadcast address | Sends to all hosts in the local IPv4 network. Host bits are all 1. |
For 192.168.1.0/24, the network address is 192.168.1.0, usable host addresses are 192.168.1.1 through 192.168.1.254, and the broadcast address is 192.168.1.255.
IPv4 Communication Types
| Type | Description |
|---|---|
| Unicast | One source sends to one destination. |
| Broadcast | One source sends to all hosts in the local network. |
| Multicast | One source sends to a selected group of receivers. |
Types of IPv4 Addresses
IPv4 addresses may be public or private.
| Private Range | Prefix |
|---|---|
| 10.0.0.0 to 10.255.255.255 | 10.0.0.0/8 |
| 172.16.0.0 to 172.31.255.255 | 172.16.0.0/12 |
| 192.168.0.0 to 192.168.255.255 | 192.168.0.0/16 |
Private addresses are used inside organizations and homes. They are not routed directly on the public internet. Network Address Translation (NAT) is commonly used when private hosts access the internet.
Other special address categories include loopback addresses, link-local addresses, and experimental or reserved ranges.
Assignment of IP Addresses
IPv4 addresses can be assigned manually or automatically.
| Method | Description |
|---|---|
| Static assignment | An administrator manually configures the address. |
| Dynamic assignment | DHCP automatically provides IP settings. |
Static addressing is common for routers, servers, printers, and infrastructure devices. DHCP is common for user devices.
Network Segmentation
Network segmentation divides a larger network into smaller subnets. Segmentation helps improve organization, security, broadcast control, and address management.
Subnetting borrows bits from the host portion to create additional network bits.
Subnetting Basics
A prefix length shows how many bits are used for the network portion.
| Prefix | Subnet Mask | Usable Hosts per Subnet |
|---|---|---|
| /24 | 255.255.255.0 | 254 |
| /25 | 255.255.255.128 | 126 |
| /26 | 255.255.255.192 | 62 |
| /27 | 255.255.255.224 | 30 |
| /28 | 255.255.255.240 | 14 |
| /29 | 255.255.255.248 | 6 |
| /30 | 255.255.255.252 | 2 |
Usable hosts are calculated as:
2^(host bits) - 2
The subtraction accounts for the network address and broadcast address.
Subnetting Example
Requirement: Split 192.168.1.0/24 into four equal subnets.
Borrow 2 host bits because 2^2 = 4. The new prefix is /26.
| Subnet | Network Address | Usable Host Range | Broadcast |
|---|---|---|---|
| 1 | 192.168.1.0/26 | 192.168.1.1 - 192.168.1.62 | 192.168.1.63 |
| 2 | 192.168.1.64/26 | 192.168.1.65 - 192.168.1.126 | 192.168.1.127 |
| 3 | 192.168.1.128/26 | 192.168.1.129 - 192.168.1.190 | 192.168.1.191 |
| 4 | 192.168.1.192/26 | 192.168.1.193 - 192.168.1.254 | 192.168.1.255 |
VLSM
Variable Length Subnet Masking (VLSM) allows different subnet sizes inside the same larger address block. This saves addresses because each subnet can be sized according to need.
A common VLSM strategy is to assign the largest subnet first, then continue with smaller requirements.
Subnetting Practice
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VLSM Design Activity
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Review Questions
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