Private IP Address Ranges

Private IP addresses are reserved for internal network use and are not routable on the public internet. RFC 1918 defines three private address ranges for IPv4, while additional special-use ranges serve specific purposes like link-local addressing and loopback testing.

RFC 1918 Private Ranges

These three ranges are defined by RFC 1918 for private internets. They will never be assigned as public addresses.

Quick Lookup Table

CIDR Block	First IP	Last IP	Addresses	Type
10.0.0.0/8	10.0.0.0	10.255.255.255	16,777,216	Private
172.16.0.0/12	172.16.0.0	172.31.255.255	1,048,576	Private
192.168.0.0/16	192.168.0.0	192.168.255.255	65,536	Private

Other Special-Use IPv4 Ranges

Beyond RFC 1918, several other address ranges have special purposes and are not routable on the public internet.

CIDR Block	Range	Purpose	RFC
127.0.0.0/8	127.0.0.0 - 127.255.255.255	Loopback Local host (typically 127.0.0.1)	RFC 1122
169.254.0.0/16	169.254.0.0 - 169.254.255.255	Link-Local Auto-configured when DHCP fails	RFC 3927
100.64.0.0/10	100.64.0.0 - 100.127.255.255	CGN Carrier-grade NAT (ISP internal)	RFC 6598
192.0.0.0/24	192.0.0.0 - 192.0.0.255	IETF Protocol Protocol assignments	RFC 6890
192.0.2.0/24	192.0.2.0 - 192.0.2.255	Documentation TEST-NET-1 for examples	RFC 5737
198.51.100.0/24	198.51.100.0 - 198.51.100.255	Documentation TEST-NET-2 for examples	RFC 5737
203.0.113.0/24	203.0.113.0 - 203.0.113.255	Documentation TEST-NET-3 for examples	RFC 5737
198.18.0.0/15	198.18.0.0 - 198.19.255.255	Benchmarking Network device testing	RFC 2544
224.0.0.0/4	224.0.0.0 - 239.255.255.255	Multicast One-to-many delivery	RFC 5771
240.0.0.0/4	240.0.0.0 - 255.255.255.254	Reserved Future use (Class E)	RFC 1112
255.255.255.255/32	255.255.255.255	Broadcast Limited broadcast address	RFC 919
0.0.0.0/8	0.0.0.0 - 0.255.255.255	This Network Source only, for DHCP/boot	RFC 1122

IPv6 Private/Special Ranges

Prefix	Purpose	IPv4 Equivalent
::1/128	Loopback Localhost	127.0.0.1
fc00::/7	Unique Local Private IPv6 (ULA)	10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16
fe80::/10	Link-Local Auto-configured, single link only	169.254.0.0/16
::ffff:0:0/96	IPv4-Mapped IPv4 addresses in IPv6 format	N/A
2001:db8::/32	Documentation Examples and documentation	192.0.2.0/24, 198.51.100.0/24, 203.0.113.0/24
ff00::/8	Multicast One-to-many delivery	224.0.0.0/4

Common Network Configurations

Is This IP Private?

# Quick regex check for private IPv4
# 10.x.x.x
^10\.([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])\.([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])\.([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])$

# 172.16.x.x - 172.31.x.x
^172\.(1[6-9]|2[0-9]|3[0-1])\.([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])\.([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])$

# 192.168.x.x
^192\.168\.([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])\.([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])$

# Bash function to check if IP is private
is_private_ip() {
    local ip=$1
    if [[ $ip =~ ^10\. ]] || \
       [[ $ip =~ ^172\.(1[6-9]|2[0-9]|3[0-1])\. ]] || \
       [[ $ip =~ ^192\.168\. ]]; then
        echo "Private"
    else
        echo "Public (or special-use)"
    fi
}

# Usage
is_private_ip "192.168.1.100"  # Private
is_private_ip "8.8.8.8"        # Public