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IPv4 Addressing

Updated Sep 17, 20261 min readipv4 · dhcp · apipa · rfc1918

On this page
  1. IPv4 Address
  2. Dynamic Host Configuration Protocol (DHCP)
  3. Private IP (RFC 1918)
  4. Automatic Private IP Addressing (APIPA)
  5. Loopback / Localhost

IPv4 Address

An IPv4 address is a unique identifier made up of a 32-bit number written as four octets (e.g., 192.168.1.10). Each octet ranges from 0–255.

Dynamic Host Configuration Protocol (DHCP)

A DHCP server is a network server that automatically assigns IP addresses and other network configuration parameters to devices (clients) on a network. Its main job is to eliminate the need for a network administrator to manually assign IP addresses to every single device.

Private IP (RFC 1918)

Used inside local networks (LANs) and are not routable on the public internet — must go through NAT (Network Address Translation).

Automatic Private IP Addressing (APIPA)

When a Windows device can't reach a DHCP server, it auto-assigns itself an IP address in the 169.254.0.0/16 range.

If you see an IP address starting with 169.254, your device has given itself an APIPA address. (Range: 169.254.0.1 – 169.254.255.254.)

APIPA is activated when the device's attempt to get a "real" IP address fails completely. This is usually due to:

  • DHCP Server is Down or Unreachable: The server that gives out IP addresses is offline.
  • Network Cable Issue: A faulty Ethernet cable can prevent communication with the DHCP server.
  • Switch/Router Problem: The network equipment between the device and the DHCP server has failed.
  • Driver or NIC Issue: A problem with the device's own network card or its software.

Loopback / Localhost

Loopback is used to test network functionality on your own device — data is sent out and received back internally. Range: 127.0.0.0 – 127.255.255.255

Related notes