Modern Networks - Classless Inter-Domain Routing, CIDR
| CIDR | Host bits | Netmask | Addresses in subnet | Typical usage |
|---|---|---|---|---|
| /8 | 24 | 255.0.0.0 | 16,777,216 = 224 | Largest block allocation made by IANA |
| /9 | 23 | 255.128.0.0 | 8,388,608 = 223 | |
| /10 | 22 | 255.192.0.0 | 4,194,304 = 222 | |
| /11 | 21 | 255.224.0.0 | 2,097,152 = 221 | |
| /12 | 20 | 255.240.0.0 | 1,048,576 = 220 | |
| /13 | 19 | 255.248.0.0 | 524,288 = 219 | |
| /14 | 18 | 255.252.0.0 | 262,144 = 218 | |
| /15 | 17 | 255.254.0.0 | 131,072 = 217 | |
| /16 | 16 | 255.255.0.0 | 65,536 = 216 | |
| /17 | 15 | 255.255.128.0 | 32,768 = 215 | ISP / large business |
| /18 | 14 | 255.255.192.0 | 16,384 = 214 | ISP / large business |
| /19 | 13 | 255.255.224.0 | 8,192 = 213 | ISP / large business |
| /20 | 12 | 255.255.240.0 | 4,096 = 212 | Small ISP / large business |
| /21 | 11 | 255.255.248.0 | 2,048 = 211 | Small ISP / large business |
| /22 | 10 | 255.255.252.0 | 1,024 = 210 | |
| /23 | 9 | 255.255.254.0 | 512 = 29 | |
| /24 | 8 | 255.255.255.0 | 256 = 28 | Large LAN |
| /25 | 7 | 255.255.255.128 | 128 = 27 | Large LAN |
| /26 | 6 | 255.255.255.192 | 64 = 26 | Small LAN |
| /27 | 5 | 255.255.255.224 | 32 = 25 | Small LAN |
| /28 | 4 | 255.255.255.240 | 16 = 24 | Small LAN |
| /29 | 3 | 255.255.255.248 | 8 = 23 | Smallest multi-host network |
| /30 | 2 | 255.255.255.252 | 4 = 22 | "Glue network" (point to point links) |
| /31 | 1 | 255.255.255.254 | 2 = 21 | Rarely used, point to point links (RFC 3021) |
| /32 | 0 | 255.255.255.255 | 1 = 20 | Host route |
Special Purpose IP addresses (reserved)
| Address block (CIDR) | Range | Number of Addresses | Scope | Purpose |
|---|---|---|---|---|
| 0.0.0.0/8 | 0.0.0.0 – 0.255.255.255 |
16,777,216 | software | Used for broadcast messages to the current ("this") network as specified by RFC 1700, page 4. |
| 10.0.0.0/8 | 10.0.0.0 – 10.255.255.255 |
16,777,216 | private network | Used for local communications within a private network as specified by RFC 1918. See Private IP address space section below. |
| 100.64.0.0/10 | 100.64.0.0 – 100.127.255.255 |
4,194,304 | private network | Used for communications between a service provider and its subscribers when using a Carrier-grade NAT, as specified by RFC 6598. |
| 127.0.0.0/8 | 127.0.0.0 – 127.255.255.255 |
16,777,216 | host | Used for loopback addresses to the local host, as specified by RFC 990. |
| 169.254.0.0/16 | 169.254.0.0 – 169.254.255.255 |
65,536 | subnet | Used for link-local addresses between two hosts on a single link when no IP address is otherwise specified, such as would have normally been retrieved from a DHCP server, as specified by RFC 3927. |
| 172.16.0.0/12 | 172.16.0.0 – 172.31.255.255 |
1,048,576 | private network | Used for local communications within a private network as specified by RFC 1918. See Private IP address space section below. |
| 192.0.0.0/24 | 192.0.0.0 – 192.0.0.255 |
256 | private network | Used for the IANA IPv4 Special Purpose Address Registry as specified by RFC 5736 |
| 192.0.2.0/24 | 192.0.2.0 – 192.0.2.255 |
256 | documentation | Assigned as "TEST-NET" in RFC 5737 for use solely in documentation and example source code and should not be used publicly. |
| 192.88.99.0/24 | 192.88.99.0 – 192.88.99.255 |
256 | Internet | Used by 6to4 anycast relays as specified by RFC 3068. |
| 192.168.0.0/16 | 192.168.0.0 – 192.168.255.255 |
65,536 | private network | Used for local communications within a private network as specified by RFC 1918. See Private IP address space section below. |
| 198.18.0.0/15 | 198.18.0.0 – 198.19.255.255 |
131,072 | private network | Used for testing of inter-network communications between two separate subnets as specified in RFC 2544. |
| 198.51.100.0/24 | 198.51.100.0 – 198.51.100.255 |
256 | documentation | Assigned as "TEST-NET-2" in RFC 5737 for use solely in documentation and example source code and should not be used publicly. |
| 203.0.113.0/24 | 203.0.113.0 – 203.0.113.255 |
256 | documentation | Assigned as "TEST-NET-3" in RFC 5737 for use solely in documentation and example source code and should not be used publicly. |
| 224.0.0.0/4 | 224.0.0.0 – 239.255.255.255 |
268,435,456 | Internet | Reserved for multicast assignments as specified in RFC 5771.
233.252.0.0/24 is assigned as "MCAST-TEST-NET" for use solely in documentation and example source code. |
| 240.0.0.0/4 | 240.0.0.0 – 255.255.255.254 |
268,435,455 | n/a | Reserved for future use, as specified by RFC 6890. |
| 255.255.255.255/32 | 255.255.255.255 | 1 | n/a | Reserved for the "limited broadcast" destination address, as specified by RFC 6890. |
Private IP address space
Most clients will never see private IP address space in use on the Mean Servers network but rather our public space instead. This is because this space is only accessible locally and would be used to connect local machines instead. The only time you will see this type of space in use is when you have specifically requested a private network to be setup such as between dedicated servers, VPS's, or colocated servers. Private networks within the Mean Servers network can be useful if you have many services with us and want data to be rapidly transferred between said services without going out to the public internet or have the transfer counted against your monthly quota. For information on setting up a private network between services, open a support ticket. Private networks can be setup free of charge for VPS clients, a small one time charge for dedicated server or colocation customers.
| RFC1918 name | IP address range | number of addresses | largest CIDR block (subnet mask) | host id size | mask bits |
classful description |
|---|---|---|---|---|---|---|
| 24-bit block | 10.0.0.0 - 10.255.255.255 | 16,777,216 | 10.0.0.0/8 (255.0.0.0) | 24 bits | 8 bits | single class A network |
| 20-bit block | 172.16.0.0 - 172.31.255.255 | 1,048,576 | 172.16.0.0/12 (255.240.0.0) | 20 bits | 12 bits | 16 contiguous class B networks |
| 16-bit block | 192.168.0.0 - 192.168.255.255 | 65,536 | 192.168.0.0/16 (255.255.0.0) | 16 bits | 16 bits | 256 contiguous class C networks |
Old School - Classful Networks
Although classful networks haven't existed for more than a decade, it seems referencing these old school classful blocks can be common for the misinformed. We provide this information simply to educate those referencing these old classful networks, albeit improperly, to better educate them as the equivalent as the classless state that the modern internet now uses. Please see the CIDR notation as to how to reference these network sizes in the future.
| Class | Leading bits | Start | End | Default Subnet Mask in dotted decimal | CIDR notation |
|---|---|---|---|---|---|
| A | 0 | 0.0.0.0 | 127.255.255.255 | 255.0.0.0 | /8 |
| B | 10 | 128.0.0.0 | 191.255.255.255 | 255.255.0.0 | /16 |
| C | 110 | 192.0.0.0 | 223.255.255.255 | 255.255.255.0 | /24 |
| D | 1110 | 224.0.0.0 | 239.255.255.255 | not defined | not defined |
| E | 1111 | 240.0.0.0 | 255.255.255.255 | not defined | not defined |
