RFC 1918 private address
RFC 1918 reserves three blocks of IPv4 address space -- 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16 -- for use inside private networks, never to be routed on the public internet. Any organization or home network can reuse these same addresses internally without coordinating with anyone else, which is what makes NAT (network address translation) necessary at the boundary: a router rewrites a private source address to its one public address before traffic leaves the network, then reverses the mapping for replies. Seeing one of these ranges as a device's own address is normal and expected behind a home router or office firewall. Seeing one show up where a public-facing address is expected instead usually signals a misconfigured NAT, proxy, or double-NAT setup rather than a real internet-reachable host.
By AdminKit team, Netbase JSC · Updated