IPv4 Subnetting and Special Purpose IP Addresses

This reference sheet is intended as a quick use guide when working with IPv4. Although most clients will never need to worry about subnets or subnetting, this information can be useful for our dedicated server clients, those running a VPN (virtual private network), adding additional IP addresses to control panels, and anything requiring some network expertise.

Modern Networks - Classless Inter-Domain Routing, CIDR

CIDRHost bitsNetmaskAddresses in subnetTypical 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)RangeNumber of AddressesScopePurpose
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 nameIP address rangenumber of addresseslargest CIDR block (subnet mask)host id sizemask bits

classful description
(old school)

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.

ClassLeading bitsStartEndDefault Subnet Mask in dotted decimalCIDR 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
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