Class B IP Address
Class B IP Address Definition
A Class B IP address is a type of IPv4 address from a legacy classification system that organized IPs into classes. Class B IP addresses range from 128.0.0.0 to 191.255.255.255 and allow for 214 (16,384) different networks, each with 216 (65,534) usable addresses. They were designed for medium-sized networks, like universities or corporations.
The class-based addressing system was mostly replaced by CIDR (Classless Inter-Domain Routing) in the early 1990s. The new system is more efficient because it allows for much more precise allotting of IP addresses, so they don’t go to waste.
How a Class B IP Address Works
A class B IP address has the same base structure as all other IPv4 addresses—it has 32 bits, separated into 4 octets. The first two octets make up the network ID, which uniquely identifies a network. The last two octets make up the host ID, which identifies an individual device on the network. For example, in the class B IP address 191.198.0.25, the network ID would be 191.198 (or 191.198.0.0 in some notation), while the host ID would be 0.25.
Where Are Class B IP Addresses Used?
Originally, class B IP addresses were assigned to organizations with thousands of devices on the same network, such as universities, government agencies, and large companies. Because each class B network can handle up to 65,534 usable addresses, they were often split into smaller blocks for the sake of efficiency.
While class B IP addresses and the classful addressing system are now mostly obsolete, there’s still some form of legacy use. For example, routers might give connected devices IP addresses from the class B private IP range (172.16.0.0 to 172.31.255.255).
Class B IP Addresses vs Other IP Addresses
| IP range | Hosts per network | Number of networks | Use cases | |
| Class A IP Address | 0.0.0.0 to 127.255.255.255 | 16,777,214 | 128 (126 usable) | Large organizations and ISPs |
| Class B IP Address | 128.0.0.0 to 191.255.255.255 | 65,536 (65,534 usable) | 16,384 | Medium to large organizations and ISPs |
| Class C IP Address | 192.0.0.0 to 223.255.255.255 | 254 | 2,097,152 | LANs, office networks, and small websites |
| Class D IP Address | 224.0.0.0 to 239.255.255.255 | Not applicable | Not applicable | Multicasting (video conferencing, gaming) |
| Class E IP Address | 240.0.0.0 to 255.255.255.255 | Not applicable | Not applicable | Experimental, not intended for public use |
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FAQ
Yes, but very rarely. Some older networks in academia or enterprises still use class B IP addresses. Because there’s a limited number of possible IPv4 addresses, class B networks are typically split into smaller subnets to reduce wastefulness. Newer networks usually use CIDR (Classless Inter-Domain Routing) for more flexibility and efficiency.
Class B addresses range from 128.0.0.0 to 191.255.255.255. The first octet has to be between 128 (10000000) and 191 (10111111) because a class B IP address always starts with 10. The first two octets define the network, while the remaining two identify unique devices on the network. This range covers 16,384 networks, each supporting up to 65,534 usable addresses.
Class B IP addresses always start with 10 in their first two bits because of the old system of determining IP address classes. When the classful addressing system was developed, the classes were identified by the first bits of their IP address ranges. For example, class A IP addresses started with 0, class B addresses with 10, class C with 110, and so on.
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