IP Class Identifier — TechKnowSurge

About this interactive

Every IPv4 address announces its class in its first octet, and once you can read that octet the rest follows: 1-126 is Class A, 128-191 is Class B, 192-223 is Class C, 224-239 is Class D for multicast, and 240 and up is Class E, reserved. That is one rule, applied fifteen times, and it is the foundation the whole of subnetting is built on. But two things sit on top of it, and this activity is really about those. The first is that some ranges are carved out and outrank the class they numerically fall inside. 127.0.0.1 is inside Class A's span, and 169.254.10.25 is inside Class B's, yet neither belongs there — loopback and APIPA are special-purpose ranges with their own meaning, and a special range always wins over the class that surrounds it. The second is that public and private are a separate question from class, not the same one. Classes A, B, and C each carry both: 10.0.0.1 and 8.8.8.8 are both Class A, and only one of them is RFC 1918 private. Sort by class first, then ask whether the address is routable. Two independent axes, asked at the same time, which is exactly how a real address arrives.

What you'll learn

Classify IPv4 addresses by class (A-E) using the first-octet range
Identify the special-purpose IPv4 ranges: RFC 1918 private, 127.x loopback, and 169.254.x APIPA
Distinguish public from private addresses within Classes A, B, and C

Aligned to

CompTIA Network+

1.7 Given a scenario, use appropriate IPv4 network addressing.

CompTIA A+ Core 1

2.6 Compare and contrast common network configuration concepts.

2.5 Given a scenario, install and configure basic wired/wireless SOHO networks.

Cisco CCNA

1.6 Configure and verify IPv4 addressing and subnetting

1.7 Describe private IPv4 addressing

Key terms

IPv4 Address Class: One of five categories (A–E) into which IPv4 addresses are grouped based on leading bit patterns, each defining a specific range of addresses and a fixed network-to-host bit boundary.
Classful Addressing: An early IPv4 addressing scheme that divided the address space into fixed classes (A, B, and C for hosts; D for multicast; E reserved) based on the leading bits of the address, with each class defining a fixed boundary between the network and host portions. Classful addressing was replaced by CIDR because it wasted large blocks of address space.
Class A Network: An IPv4 address class using the range 1–126 in the first octet, with a default subnet mask of 255.0.0.0, providing a large number of host addresses.
Class B Network: An IPv4 address class with a default subnet mask of 255.255.0.0 (/16), supporting up to 65,534 usable hosts on a single network.
Private IPv4 Address: An IP address from RFC 1918 ranges (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16) that is not routable on the public internet and must be translated before traversing it.
Public IP Address: A globally unique IP address assigned to a device or network that is routable and reachable across the public internet.
Loopback Address: The reserved IPv4 address 127.0.0.1 (within the 127.0.0.0/8 range) that a device uses to send traffic to itself, allowing the local network stack to be tested without sending packets onto a physical network. Pinging 127.0.0.1 is a quick way to verify that a device's TCP/IP stack is functioning.
Automatic Private IP Addressing: A feature that automatically assigns a device an IP address in the 169.254.0.0/16 range when it cannot obtain an address from a DHCP server. APIPA allows limited local-network communication but does not provide internet access.
RFC 1918: The internet standard that defines three private IPv4 address ranges reserved for use within private networks and not routable on the public internet.
Multicast: A transmission type in which data is sent from one source to a specific group of devices that have subscribed to a multicast group address, rather than to all devices or just one. This differs from broadcast (all devices) and unicast (one device).
IPv4: The fourth version of the Internet Protocol, using 32-bit addresses that provide approximately 4.3 billion unique addresses.

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