What are the private IP ranges, and what are loopback and link-local addresses?
Private ranges are 10.0.0.0/8, 172.16.0.0/12 (172.16.0.0 to 172.31.255.255) and 192.168.0.0/16. They are not routed on the public internet. Loopback is 127.0.0.0/8 (your own machine) and link-local is 169.254.0.0/16 (self-assigned when DHCP fails).
Explain it simply
Private addresses are like internal extension numbers in a company. Many offices can use extension 204 without clashing, because outsiders cannot dial them directly. Public addresses are like full phone numbers with the city code.
Example
10.0.0.0/8 10.0.0.0 - 10.255.255.255 16,777,216 addresses
172.16.0.0/12 172.16.0.0 - 172.31.255.255 1,048,576 addresses
192.168.0.0/16 192.168.0.0 - 192.168.255.255 65,536 addresses
127.0.0.0/8 loopback, 127.0.0.1 = "localhost"
169.254.0.0/16 link-local (APIPA)Your home Wi-Fi router usually hands out 192.168.x.x addresses to your phone and laptop, and NAT converts them to the one public address your ISP gave the router. Many college and company networks use 10.x.x.x.
172.32.0.1 is not private. The 172 range stops at 172.31.255.255, which is a frequent trick question.
What to say in the interview
"RFC 1918 reserves 10/8, 172.16/12 and 192.168/16 for private use. They need NAT to reach the internet. 127.0.0.1 never leaves the machine, and 169.254.x.x means DHCP failed and the OS assigned itself an address."
Common mistakes
- Thinking all 172.x.x.x addresses are private.