How IP Addresses Work
Reserved and Special-Use IP Addresses
Certain IP addresses are set aside for specific jobs and never route across the public internet. Recognizing them saves a lot of confusion.
Loopback: talking to yourself
The address 127.0.0.1 (and the whole 127.0.0.0/8 block) is the loopback, meaning "this device." Traffic sent there never leaves the machine. Developers use localhost, which resolves to loopback, to test software on their own computer. In IPv6 the loopback is written ::1.
Private ranges: local networks
Three IPv4 ranges are reserved for private networks and are never used on the public internet:
10.0.0.0/8172.16.0.0/12192.168.0.0/16
Your home router almost certainly hands out addresses from 192.168.x.x or 10.x.x.x.
Link-local: the emergency address
If a device cannot get an address from a DHCP server, it can assign itself a link-local address — 169.254.x.x in IPv4, or fe80:: in IPv6. These work only on the immediate network segment and never route further. Seeing a 169.254 address usually means a device failed to get a real one.
Other special addresses
0.0.0.0— "this network" or "any address," depending on context.- The last address in a subnet — the broadcast address, reaching all devices at once.
100.64.0.0/10— reserved for carrier-grade NAT used by some ISPs.- Documentation ranges like
192.0.2.0/24— reserved for examples (which is why guides, including this one, use them).
Why it's worth knowing
When you glance at an address and recognize it as loopback, private, or link-local, you immediately understand its scope — and you know it will never be the public IP the wider internet sees. That instinct makes troubleshooting home and office networks far quicker.