🏷️ Network Class Identifier
Enter an IPv4 address to identify its legacy classful network class (A, B, C, D multicast or E reserved) and whether it falls in a private (RFC 1918) range.
The class is decided by the leading bits
Only the first octet is read, and only its top bits matter. Each class is defined by a prefix of fixed bits, which is what produces the familiar first-octet boundaries:
0xxxxxxx -> A 1 - 126 (127 is loopback)
10xxxxxx -> B 128 - 191
110xxxxx -> C 192 - 223
1110xxxx -> D 224 - 239 multicast
1111xxxx -> E 240 - 255 reserved192 is 11000000, so the leading 110 puts 192.168.1.10 in class C. The counts fall out of the same split: class B fixes 2 of its 16 network bits, leaving 2^14 = 16,384 networks of 65,534 hosts, while class C fixes 3 of 24, leaving 2^21 = 2,097,152 networks of 254 hosts each.
Class, mask and privacy are three separate things
| Class | First octet | Old default | Usable hosts |
|---|---|---|---|
| A | 1-126 | /8 | 16,777,214 |
| B | 128-191 | /16 | 65,534 |
| C | 192-223 | /24 | 254 |
| D | 224-239 | none | multicast groups |
| E | 240-255 | none | reserved |
The "old default" column is history. Since CIDR arrived in 1993 the mask travels with the route, so 10.1.2.3 is far more often a /24 on somebody's LAN than the /8 its class implies. The private flag is independent again: 10.0.0.0/8 sits in class A, 172.16.0.0/12 covers 16 class B networks, and 192.168.0.0/16 covers 256 class C ones.
Frequently asked questions
Is 192.168.1.1 a class B or class C address?
Class C. The first octet 192 falls in 192-223, and it is also private under RFC 1918, which is a separate property from its class.
How many hosts can a class A network hold?
16,777,214. A classful /8 leaves 24 host bits, so 2^24 = 16,777,216 addresses minus the network and broadcast addresses.
Do IP address classes still matter?
Only for exams and for reading old documentation. Routing has been classless since 1993, so a prefix length is always carried explicitly and no router infers a mask from the first octet any more.