Which of the following is an invalid IP address?

Correct answer: 256.10.12.5 is invalid

Why:

IPv4 addresses use four octets separated by dots. Each octet must be an integer between 0 and 255 inclusive.

• 100.0.10.32 — valid: all octets (100, 0, 10, 32) are within 0–255.

• 255.255.255.10 — valid: all octets (255, 255, 255, 10) are within 0–255. (In networking contexts, octets of 255 can be special, but the address is syntactically valid.)

• 192.168.10.15 — valid: all octets are within range and this falls in the private 192.168.0.0/16 block.

• 256.10.12.5 — invalid: the first octet is 256, which is greater than the maximum allowed value 255.