IP addressing is the map a device uses to decide what is local and what must go through a router. A useful explanation connects the address to its prefix/subnet mask, default gateway, DHCP lease, DNS settings and route table. Looking at the address alone is rarely enough.

Not every special-looking address means the same thing

RFC 1918 defines private IPv4 ranges used inside networks. 169.254/16 is link-local fallback space. 100.64/10 is shared service-provider space used for address sharing such as CGNAT. IPv6 adds link-local, global and other scopes. Treating all non-public-looking addresses as “router IPs” creates bad troubleshooting and bad content.

Stable addressing without collisions

DHCP reservations are often the cleanest way to keep printers, NAS systems and servers predictable while retaining automatic gateway and DNS updates. Manual static addressing remains useful when designed carefully and documented outside dynamic assignment.

Addressing guides

Know which “special” range you are looking at

RFC 1918 private space, IPv4 link-local 169.254/16, shared provider space 100.64/10, loopback, and IPv6 link-local/ULA ranges all have different purposes. A non-public address is not automatically a router address, and a private-looking WAN address can be evidence of another NAT boundary.

Design addresses around routes, not visual patterns

Use prefixes mathematically, keep DHCP pools and reservations documented, and check overlap with VPNs or second sites before changing a LAN. Two addresses that begin with the same three octets are not always in the same subnet, and two different-looking ranges can still overlap depending on prefix length.

Video walkthrough for IP Addressing, DHCP & Subnetting Center

Visual foundation for network/host bits, masks, CIDR and subnetting. Use the calculator on this site for the exact arithmetic after understanding the concept.