IPv4
IPv4 (32 bits)
What is IPv4?
IPv4 (Internet Protocol Version 4) is the most widely used protocol for identifying devices on a network and routing data across the Internet.
An IP address is like a home's mailing address. It tells data where to go and where it came from.
IPv4 Chart
Class IP Range Subnet Mask CIDR Hosts Networks Use for
A 1-126 255.0.0.0 /8 126 16,777,214 Large NetworksB 128-191 255.255.0.0 /16 16,384 65,536 Medium NetworksC 192-223 255.255.255.0 /24 2,097,152 254 Small NetworksD 224-239 Multicast NetworksE 240-255 Reserved Networks
What is 127.0.0.1? 127.0.0.1 is called the loopback address or localhost in IPv4 networking. It is a special IP address that always refers to your own computer.
What is APIPA? APIPA stands for Automatic Private IP Addressing. APIPA is a feature in Windows that automatically assigns an IP address to a device when it cannot obtain one from a DHCP (Dynamic Host Configuration Protocol) server. How APIPA Works Normally: Plain Text Computer → DHCP Server → IP Address Assigned Show more lines If the DHCP server is unavailable: Plain Text Computer → No DHCP Response ↓ APIPA assigns an address Show more lines The computer automatically assigns itself an IP address in the APIPA range. APIPA Address Range Plain Text 169.254.0.1 to 169.254.255.254 Show more lines Example: Plain Text 169.254.125.50 Show more lines If you see an IP address beginning with 169.254.x.x, it usually means the device could not contact a DHCP server. Why APIPA Exists APIPA allows devices on the same local network to communicate with each other even when DHCP is unavailable. However, APIPA devices typically: Cannot reach the Internet Cannot communicate outside their local network Cannot use routers effectively Common Causes of an APIPA Address DHCP server is offline Network cable unplugged Wi-Fi connectivity issues DHCP service failure Network configuration problems Example Troubleshooting Scenario You run: Shell ipconfig Show more lines and see: Plain Text IPv4 Address. . . . . . : 169.254.15.20 Show more lines This indicates your computer failed to obtain an address from DHCP. A network administrator would check: Network connection Router or switch status DHCP server availability Cable or wireless connection issues APIPA vs Private IP Addresses Type Address RangeAPIPA 169.254.0.0/16 Private Class A 10.0.0.0/8 Private Class B 172.16.0.0 - 172.31.255.255 Private Class C 192.168.0.0/16 Network+ Exam Tip Remember: APIPA = 169.254.x.x Assigned automatically when DHCP fails Used for local communication only Usually indicates a DHCP or connectivity problem Easy Memory Trick Think: Plain Text 169.254 = "DHCP Failed" Show more lines Whenever you see a 169.254.x.x address, your first troubleshooting step should be to verify that the device can communicate with the DHCP server.
IPv4 Address Format An IPv4 address consists of 32 bits and is typically written as four decimal numbers separated by periods. Example: Plain Text 192.168.1.10 Show more lines Each number (called an octet) ranges from: Plain Text 0 to 255 Show more lines Examples of IPv4 addresses: Plain Text 10.0.0.1 172.16.0.1 192.168.1.100 8.8.8.8 Show more lines How IPv4 Works When your computer sends data: The data is broken into packets. Each packet contains a source IP address. Each packet contains a destination IP address. Routers use the destination address to forward the packet. The packet reaches the intended device. Plain Text PC (192.168.1.10) | Router | Internet | Server (142.250.190.78) Show more lines Public vs Private IPv4 Addresses Private Addresses Used inside homes and businesses. Ranges: Private IP Addresses (RFC 1918) 10.0.0.0 – 10.255.255.255 172.16.0.0 – 172.31.255.255 192.168.0.0 – 192.168.255.255 Show more lines Example: Plain Text 192.168.1.50 Show more lines Public Addresses Used on the Internet and assigned by Internet Service Providers (ISPs). Example: Plain Text 8.8.8.8 Show more lines IPv4 Structure An IPv4 address has two parts: Plain Text Network Portion Host Portion Show more lines Example: Plain Text 192.168.1.25/24 Show more lines Network = 192.168.1 Host = 25 Subnet Masks A subnet mask identifies the network and host portions. Common subnet masks: Plain Text 255.0.0.0 (/8) 255.255.0.0 (/16) 255.255.255.0 (/24) Show more lines Example: Plain Text IP Address: 192.168.1.25 Subnet Mask: 255.255.255.0 Show more lines Why IPv4 Is Being Replaced IPv4 supports approximately: Plain Text 4.3 billion addresses Show more lines Because of the huge growth of the Internet, IPv4 addresses are limited. To solve this problem, IPv6 was introduced. IPv4 vs IPv6 Feature IPv4 IPv6Address Length 32-bit 128-bit Example 192.168.1.1 2001:db8::1 Total Addresses ~4.3 Billion 340 Undecillion+ Widely Used Yes Growing Network+ Exam Tip Remember these facts: IPv4 = 32-bit address 4 octets 0-255 per octet Written in dotted decimal format Used to identify devices on a network Example If your laptop has: Plain Text IP Address: 192.168.1.100 Subnet Mask: 255.255.255.0 Default Gateway: 192.168.1.1 Show more lines Then: Your laptop's identity on the network is 192.168.1.100 The router is 192.168.1.1 Devices on the same network can communicate directly Simple definition: IPv4 is the addressing system that allows devices to communicate on networks and the Internet by giving each device a unique 32-bit IP address.
IPv4 Chart
Class IP Range Subnet Mask CIDR Hosts Networks Use for
A 1-126 255.0.0.0 /8 126 16,777,214 Large NetworksB 128-191 255.255.0.0 /16 16,384 65,536 Medium NetworksC 192-223 255.255.255.0 /24 2,097,152 254 Small NetworksD 224-239 Multicast NetworksE 240-255 Reserved Networks
What is 127.0.0.1? 127.0.0.1 is called the loopback address or localhost in IPv4 networking. It is a special IP address that always refers to your own computer.
What is APIPA? APIPA stands for Automatic Private IP Addressing. APIPA is a feature in Windows that automatically assigns an IP address to a device when it cannot obtain one from a DHCP (Dynamic Host Configuration Protocol) server. How APIPA Works Normally: Plain Text Computer → DHCP Server → IP Address Assigned Show more lines If the DHCP server is unavailable: Plain Text Computer → No DHCP Response ↓ APIPA assigns an address Show more lines The computer automatically assigns itself an IP address in the APIPA range. APIPA Address Range Plain Text 169.254.0.1 to 169.254.255.254 Show more lines Example: Plain Text 169.254.125.50 Show more lines If you see an IP address beginning with 169.254.x.x, it usually means the device could not contact a DHCP server. Why APIPA Exists APIPA allows devices on the same local network to communicate with each other even when DHCP is unavailable. However, APIPA devices typically: Cannot reach the Internet Cannot communicate outside their local network Cannot use routers effectively Common Causes of an APIPA Address DHCP server is offline Network cable unplugged Wi-Fi connectivity issues DHCP service failure Network configuration problems Example Troubleshooting Scenario You run: Shell ipconfig Show more lines and see: Plain Text IPv4 Address. . . . . . : 169.254.15.20 Show more lines This indicates your computer failed to obtain an address from DHCP. A network administrator would check: Network connection Router or switch status DHCP server availability Cable or wireless connection issues APIPA vs Private IP Addresses Type Address RangeAPIPA 169.254.0.0/16 Private Class A 10.0.0.0/8 Private Class B 172.16.0.0 - 172.31.255.255 Private Class C 192.168.0.0/16 Network+ Exam Tip Remember: APIPA = 169.254.x.x Assigned automatically when DHCP fails Used for local communication only Usually indicates a DHCP or connectivity problem Easy Memory Trick Think: Plain Text 169.254 = "DHCP Failed" Show more lines Whenever you see a 169.254.x.x address, your first troubleshooting step should be to verify that the device can communicate with the DHCP server.
IPv4 Address Format An IPv4 address consists of 32 bits and is typically written as four decimal numbers separated by periods. Example: Plain Text 192.168.1.10 Show more lines Each number (called an octet) ranges from: Plain Text 0 to 255 Show more lines Examples of IPv4 addresses: Plain Text 10.0.0.1 172.16.0.1 192.168.1.100 8.8.8.8 Show more lines How IPv4 Works When your computer sends data: The data is broken into packets. Each packet contains a source IP address. Each packet contains a destination IP address. Routers use the destination address to forward the packet. The packet reaches the intended device. Plain Text PC (192.168.1.10) | Router | Internet | Server (142.250.190.78) Show more lines Public vs Private IPv4 Addresses Private Addresses Used inside homes and businesses. Ranges: Private IP Addresses (RFC 1918) 10.0.0.0 – 10.255.255.255 172.16.0.0 – 172.31.255.255 192.168.0.0 – 192.168.255.255 Show more lines Example: Plain Text 192.168.1.50 Show more lines Public Addresses Used on the Internet and assigned by Internet Service Providers (ISPs). Example: Plain Text 8.8.8.8 Show more lines IPv4 Structure An IPv4 address has two parts: Plain Text Network Portion Host Portion Show more lines Example: Plain Text 192.168.1.25/24 Show more lines Network = 192.168.1 Host = 25 Subnet Masks A subnet mask identifies the network and host portions. Common subnet masks: Plain Text 255.0.0.0 (/8) 255.255.0.0 (/16) 255.255.255.0 (/24) Show more lines Example: Plain Text IP Address: 192.168.1.25 Subnet Mask: 255.255.255.0 Show more lines Why IPv4 Is Being Replaced IPv4 supports approximately: Plain Text 4.3 billion addresses Show more lines Because of the huge growth of the Internet, IPv4 addresses are limited. To solve this problem, IPv6 was introduced. IPv4 vs IPv6 Feature IPv4 IPv6Address Length 32-bit 128-bit Example 192.168.1.1 2001:db8::1 Total Addresses ~4.3 Billion 340 Undecillion+ Widely Used Yes Growing Network+ Exam Tip Remember these facts: IPv4 = 32-bit address 4 octets 0-255 per octet Written in dotted decimal format Used to identify devices on a network Example If your laptop has: Plain Text IP Address: 192.168.1.100 Subnet Mask: 255.255.255.0 Default Gateway: 192.168.1.1 Show more lines Then: Your laptop's identity on the network is 192.168.1.100 The router is 192.168.1.1 Devices on the same network can communicate directly Simple definition: IPv4 is the addressing system that allows devices to communicate on networks and the Internet by giving each device a unique 32-bit IP address.
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