What three blocks of addresses are defined by RFC 1918 for private network use? (Choose three.) Option 1: Class A, Class B, Class C
Option 2: Class X, Class Y, Class Z
Option 3: Block 1, Block 2, Block 3
Option 4: Private 1, Private 2, Private 3
The Correct Answer and Explanation is:
The correct answer is Option 1: Class A, Class B, Class C.
Explanation:
RFC 1918, titled “Address Allocation for Private Internets,” defines three blocks of IP addresses that are reserved for use in private networks. These addresses are not routable on the public Internet but can be used internally within organizations or private networks. This is important for network security and conserving globally unique IP addresses. The private address blocks defined by RFC 1918 are as follows:
- Class A Private Address Range:
- IP Range: 10.0.0.0 to 10.255.255.255
- Subnet Mask: 255.0.0.0 (or /8)
- Total Addresses: 16,777,216 addresses
- This block provides a large range of IP addresses, making it suitable for large organizations or networks that require a significant number of private IP addresses. The range starts with the “10” prefix, and addresses within this range are commonly used in large enterprises.
- Class B Private Address Range:
- IP Range: 172.16.0.0 to 172.31.255.255
- Subnet Mask: 255.240.0.0 (or /12)
- Total Addresses: 1,048,576 addresses
- This block is intended for medium-sized networks. The range is smaller than the Class A range, but it still provides a considerable number of private IP addresses. It is commonly used by organizations that do not need as many addresses as Class A offers.
- Class C Private Address Range:
- IP Range: 192.168.0.0 to 192.168.255.255
- Subnet Mask: 255.255.255.0 (or /24)
- Total Addresses: 65,536 addresses
- The Class C range is the most commonly used private address space, often seen in smaller networks, such as home networks, small businesses, or branch offices. It provides a limited number of addresses compared to Class A and B but is often sufficient for smaller-scale operations.
Why Other Options Are Incorrect:
- Option 2: Class X, Class Y, Class Z — This is not valid. These are not defined address classes in any RFC, including RFC 1918.
- Option 3: Block 1, Block 2, Block 3 — This is not correct because RFC 1918 specifically defines address blocks based on the class of the address, not generic “blocks.”
- Option 4: Private 1, Private 2, Private 3 — Similar to Option 3, this terminology is not used in RFC 1918.
Therefore, the correct answer is Option 1: Class A, Class B, Class C as they are the three address blocks specifically defined for private network use in RFC 1918.