IP Class Finder
Identify IP address class, type, and range
What is an IP Class Finder?
An IP Class Finder identifies the class (A, B, C, D, or E) of any IPv4 address based on its first octet. While classful addressing has been largely replaced by CIDR, understanding IP classes remains important for legacy systems and networking fundamentals. It also reports the historical default mask, private/loopback/multicast flags, and a plain-English description in one click.
How to Use This Tool
- Enter the IPv4 address, Type an address like 172.16.0.1 in the IPv4 Address field.
- Click Find Class, Class, default mask, private/loopback/multicast flags appear instantly; Reset restores the 172.16.0.1 example.
- Use the Default Mask row for context, It shows the historical classful mask, not a recommendation for modern CIDR subnetting.
Understanding the Results
Class comes from the first octet: 0–127 is A, 128–191 is B, 192–223 is C, 224–239 is D, 240–255 is E, with a plain-English Description of each. Default Mask/CIDR shows 255.0.0.0/8, 255.255.0.0/16 or 255.255.255.0/24 for A/B/C and N/A for D/E. Private Range flags 10/8, 172.16/12, 192.168/16 plus 127 loopback as Yes; Loopback is Yes only for 127.x and Multicast only for 224–239.
Tips & Best Practices
• Treat the class as background, not a subnet plan, design real subnets with the IPv4 Subnet Calculator and CIDR prefixes.
• Class D never yields usable host addresses; if you see Class D, you are looking at a multicast group, not a host.
• For certification study, memorize first-octet boundaries and the three default masks; the tool is a fast self-check.
Frequently Asked Questions
Classful addressing was replaced by CIDR in 1993, so modern networks use variable-length prefixes instead of fixed /8, /16 and /24 boundaries. Class knowledge still matters for certification exams, legacy configs with default masks, and quickly recognizing multicast (D) versus experimental (E) space.
Class A is 0–127, B is 128–191, C is 192–223, D is 224–239 and E is 240–255. The tool applies exactly these cutoffs to the first octet you enter.
127.0.0.0/8 is the loopback block, and this tool flags it as private as well as loopback so it is never mistaken for a routable address. Loopback Yes appears only for 127.x.
Class A defaults to 255.0.0.0 (/8), B to 255.255.0.0 (/16) and C to 255.255.255.0 (/24). Classes D and E have no host mask, so those rows show N/A.
Sized this for your site?
Free engineers turn these numbers into a working design, topology, hardware and quote included.