Detailed information about IPv4 and IPv6 CIDR notation
CIDR (Classless Inter-Domain Routing) notation is a compact method for specifying IP addresses and their routing suffix. Select a CIDR prefix below to view detailed information about that specific subnet size.
CIDR (Classless Inter-Domain Routing) is a method for allocating IP addresses and IP routing. It replaced the previous classful network addressing architecture and helps address the scarcity of IPv4 addresses.
The CIDR notation combines the network address with a suffix that indicates the number of bits in the prefix, for example 192.168.1.0/24.
The suffix "/24" indicates that the first 24 bits are used for the network part, leaving the remaining 8 bits for host addresses within that network.
This comprehensive table shows all IPv4 CIDR notations from /0 to /32 with their corresponding subnet masks, number of usable hosts, and available IPs for different cloud providers.
| CIDR | Subnet Mask | Usable Hosts | AWS IPs | Azure IPs | GCP IPs |
|---|---|---|---|---|---|
| /0 | 0.0.0.0 | 4,294,967,294 | 4,294,967,289 | 4,294,967,289 | 4,294,967,290 |
| /1 | 128.0.0.0 | 2,147,483,646 | 2,147,483,641 | 2,147,483,641 | 2,147,483,642 |
| /2 | 192.0.0.0 | 1,073,741,822 | 1,073,741,817 | 1,073,741,817 | 1,073,741,818 |
| /3 | 224.0.0.0 | 536,870,910 | 536,870,905 | 536,870,905 | 536,870,906 |
| /4 | 240.0.0.0 | 268,435,454 | 268,435,449 | 268,435,449 | 268,435,450 |
| /5 | 248.0.0.0 | 134,217,726 | 134,217,721 | 134,217,721 | 134,217,722 |
| /6 | 252.0.0.0 | 67,108,862 | 67,108,857 | 67,108,857 | 67,108,858 |
| /7 | 254.0.0.0 | 33,554,430 | 33,554,425 | 33,554,425 | 33,554,426 |
| /8 | 255.0.0.0 | 16,777,214 | 16,777,209 | 16,777,209 | 16,777,210 |
| /9 | 255.128.0.0 | 8,388,606 | 8,388,601 | 8,388,601 | 8,388,602 |
| /10 | 255.192.0.0 | 4,194,302 | 4,194,297 | 4,194,297 | 4,194,298 |
| /11 | 255.224.0.0 | 2,097,150 | 2,097,145 | 2,097,145 | 2,097,146 |
| /12 | 255.240.0.0 | 1,048,574 | 1,048,569 | 1,048,569 | 1,048,570 |
| /13 | 255.248.0.0 | 524,286 | 524,281 | 524,281 | 524,282 |
| /14 | 255.252.0.0 | 262,142 | 262,137 | 262,137 | 262,138 |
| /15 | 255.254.0.0 | 131,070 | 131,065 | 131,065 | 131,066 |
| /16 | 255.255.0.0 | 65,534 | 65,529 | 65,529 | 65,530 |
| /17 | 255.255.128.0 | 32,766 | 32,761 | 32,761 | 32,762 |
| /18 | 255.255.192.0 | 16,382 | 16,377 | 16,377 | 16,378 |
| /19 | 255.255.224.0 | 8,190 | 8,185 | 8,185 | 8,186 |
| /20 | 255.255.240.0 | 4,094 | 4,089 | 4,089 | 4,090 |
| /21 | 255.255.248.0 | 2,046 | 2,041 | 2,041 | 2,042 |
| /22 | 255.255.252.0 | 1,022 | 1,017 | 1,017 | 1,018 |
| /23 | 255.255.254.0 | 510 | 505 | 505 | 506 |
| /24 | 255.255.255.0 | 254 | 249 | 249 | 250 |
| /25 | 255.255.255.128 | 126 | 121 | 121 | 122 |
| /26 | 255.255.255.192 | 62 | 57 | 57 | 58 |
| /27 | 255.255.255.224 | 30 | 25 | 25 | 26 |
| /28 | 255.255.255.240 | 14 | 9 | 9 | 10 |
| /29 | 255.255.255.248 | 6 | 1 | 1 | 2 |
| /30 | 255.255.255.252 | 2 | 0 | 0 | 0 |
| /31 | 255.255.255.254 | 0 (point-to-point) | 0 | 0 | 0 |
| /32 | 255.255.255.255 | 1 (single host) | 0 | 0 | 0 |
IPv6 introduces several types of addresses, each serving a specific purpose in the network. Understanding these types is crucial for proper network design and implementation.
| Address Type | Prefix | Description | Example |
|---|---|---|---|
| Global Unicast | 2000::/3 | Globally routable addresses | 2001:db8:: |
| Unique Local | fc00::/7 | Private addresses (similar to IPv4 private ranges) | fd12:3456:789a:: |
| Link-Local | fe80::/10 | Addresses for communication within a single network segment | fe80::1 |
| Multicast | ff00::/8 | One-to-many communication | ff02::1 |
| Loopback | ::1/128 | Localhost address | ::1 |
| Unspecified | ::/128 | Used when no address is specified | :: |
IPv6 addresses are structured into three main parts, each serving a specific purpose in network routing and host identification.
Assigned by your ISP, identifies your organization's network on the global internet.
Used by organizations to create up to 65,536 subnets within their allocated prefix.
Identifies individual interfaces on a subnet, often generated using EUI-64 or randomly.
IPv6 uses a 128-bit address space and CIDR notation from /0 to /128. Here is a comprehensive reference of common IPv6 prefix lengths and their uses.
| CIDR | Description | Number of /64 Subnets | Common Usage |
|---|---|---|---|
| /0 | Entire IPv6 address space | 2^64 | Default route |
| /3 | 1/8 of the IPv6 address space | 2^61 | IANA allocation |
| /12 | Regional Internet Registry allocation | 2^52 | RIR allocation |
| /16 | Large ISP allocation | 2^48 | Major ISP |
| /24 | Medium ISP allocation | 2^40 | Medium ISP |
| /32 | ISP allocation | 2^32 | ISP allocation |
| /40 | Large organization allocation | 2^24 | Large enterprise |
| /48 | Organization/Site allocation | 2^16 (65,536) | Enterprise network |
| /52 | Medium organization allocation | 2^12 (4,096) | Medium business |
| /56 | Small organization/Home network | 2^8 (256) | Small business/Home |
| /60 | Small office allocation | 2^4 (16) | Small office |
| /64 | Standard subnet size | 1 | Individual subnet |
| /80 | Small subnet allocation | 2^-16 | Specialized networks |
| /96 | IPv4-mapped IPv6 addresses | 2^-32 | IPv4/IPv6 translation |
| /112 | Very small subnet | 2^-48 | Point-to-point links |
| /126 | Point-to-point links | 2^-62 | Router interconnects |
| /127 | Point-to-point links | 2^-63 | Router interconnects |
| /128 | Single host address | 2^-64 | Loopback, anycast |