What are private IP addresses

In the Internet addressing architecture, the Internet Engineering Task Force (IETF) and the Internet Assigned Numbers Authority (IANA) have reserved various IP addresses for special purposes.

Misunderstandings about Private IP Addresses

The concepts of internal and external IP addresses are not fixed, but relative. It’s easier to understand them as private and public IP addresses or local area network and internet IP addresses.

Almost all textbooks tell us that there are three types of private IP addresses:

  • Class A: 10.0.0.0 - 10.255.255.255
  • Class B: 172.16.0.0 - 172.31.255.255
  • Class C: 192.168.0.0 - 192.168.255.255

But in fact, private IP addresses are more than these. From the Wikipedia page Reserved_IP_addresses, in the Internet addressing architecture, the Internet Engineering Task Force (IETF) and the Internet Assigned Numbers Authority (IANA) have reserved various IP addresses for special purposes.

List of Reserved IPv4 Addresses

The IPv4 addresses are shown below:

Address block CIDR Address range Number of addresses Scope RFC Description
0.0.0.0/8 0.0.0.0 – 0.255.255.255 16,777,216 Software RFC791 Current network
10.0.0.0/8 10.0.0.0 – 10.255.255.255 16,777,216 Private network RFC1918 Used for local communications within a private network
100.64.0.0/10 100.64.0.0 – 100.127.255.255 4,194,304 Private network RFC6598 Shared address space for communications between a service provider and its subscribers when using a carrier-grade NAT
127.0.0.0/8 127.0.0.0 – 127.255.255.255 16,777,216 Host RFC1122 Used for loopback addresses to the local host
169.254.0.0/16 169.254.0.0 – 169.254.255.255 65,536 Subnet RFC3927 Used for link-local addresses[5] 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
172.16.0.0/12 172.16.0.0 – 172.31.255.255 1,048,576 Private network RFC1918 Used for local communications within a private network
192.0.0.0/24 192.0.0.0 – 192.0.0.255 256 Private network RFC6890 IETF Protocol Assignments.
192.0.2.0/24 192.0.2.0 – 192.0.2.255 256 Documentation RFC5737 Assigned as TEST-NET-1, documentation and examples
192.31.196.0/24 192.31.196.0 - 192.31.196.255 256 Private network RFC7535 AS112-v4
192.52.193.0/24 192.52.193.0 - 192.52.193.255 256 Private network RFC7450 AMT
192.88.99.0/24 192.88.99.0 – 192.88.99.255 256 Internet RFC7526 Deprecated (6to4 Relay Anycast)
192.168.0.0/16 192.168.0.0 – 192.168.255.255 65,536 Private network RFC1918 Used for local communications within a private network
192.175.48.0/24 192.175.48.0 - 192.175.48.255 256 Private network RFC7534 Direct Delegation AS112 Service
198.18.0.0/15 198.18.0.0 – 198.19.255.255 131,072 Private network RFC2544 Used for benchmark testing of inter-network communications between two separate subnets
198.51.100.0/24 198.51.100.0 – 198.51.100.255 256 Documentation RFC5737 Assigned as TEST-NET-2, documentation and examples
203.0.113.0/24 203.0.113.0 – 203.0.113.255 256 Documentation RFC5737 Assigned as TEST-NET-3, documentation and examples
240.0.0.0/4 240.0.0.0 – 255.255.255.254 268,435,455 Internet RFC1112 Reserved for future use
255.255.255.255/32 255.255.255.255 1 Subnet RFC8190, RFC919 Reserved for the “limited broadcast” destination address

References

https://en.wikipedia.org/wiki/Reserved_IP_addresse
https://www.iana.org/assignments/iana-ipv4-special-registry/iana-ipv4-special-registry.xhtml
https://blog.csdn.net/winter_wu_1998/article/details/103626640
https://www.biaodianfu.com/ip.html