Examkin

Private IPv4 Addressing and RFC 1918

24 questions

All types24Multiple choice14Multiple select4Matching6
Question 21Question →

A network auditing tool generates a report listing IPv4 addresses detected on internal branch office node interfaces. Which of the following IPv4 addresses are compliant with RFC 1918 private IP addressing standards? (Select TWO.)

Select all that apply

Show answer & explanation

Answer: 10.254.1.50; 172.29.40.10

Answer

The IPv4 addresses 10.254.1.50 and 172.29.40.10 are valid RFC 1918 private IPv4 addresses.
The addresses 10.254.1.50 and 172.29.40.10 fit directly inside the RFC 1918 standard private ranges: 10.0.0.0/8 (10.0.0.0 to 10.255.255.255) and 172.16.0.0/12 (172.16.0.0 to 172.31.255.255) respectively.

Step-by-Step Solution

1
Recall the three designated RFC 1918 private IPv4 address ranges.
Class A: 10.0.0.0/8 (10.0.0.0 – 10.255.255.255), Class B: 172.16.0.0/12 (172.16.0.0 – 172.31.255.255), Class C: 192.168.0.0/16 (192.168.0.0 – 192.168.255.255).
Establishing accurate range boundaries is necessary to differentiate private non-routable IPs from public IPs.
2
Evaluate candidate address 10.254.1.50 against the RFC 1918 specifications.
10.254.1.50 begins with 10 in the first octet, making it a valid member of the 10.0.0.0/8 block.
Any IP starting with 10.x.x.x is private under RFC 1918.
3
Evaluate candidate address 172.29.40.10 against the RFC 1918 specifications.
172.29.40.10 has a second octet of 29, which lies within the inclusive 16–31 range for the 172.16.0.0/12 block.
Addresses from 172.16.0.0 through 172.31.255.255 are valid private addresses.
4
Evaluate invalid candidate addresses 172.33.1.1 and 192.169.50.25.
172.33.1.1 falls outside the 172.16–172.31 range, and 192.169.50.25 falls outside the 192.168.0.0/16 range.
Both 172.33.x.x and 192.169.x.x are public IPv4 addresses assigned on the Internet.

Key Concept

RFC 1918 Private IPv4 Address Scope
Question 22Question →

A system administrator is setting up an internal application server and needs to assign an IPv4 address from the RFC 1918 Class B private address space. Which of the following IPv4 addresses is a valid private IP address within this Class B block?

Show answer & explanation

Answer: 172.20.15.5

Answer

172.20.15.5 is a valid RFC 1918 Class B private IPv4 address.
RFC 1918 defines the Class B private IPv4 space as 172.16.0.0 to 172.31.255.255 (172.16.0.0/12). The address 172.20.15.5 falls directly inside this range because its second octet (20) is within the 16–31 boundary.

Step-by-Step Solution

1
Identify the RFC 1918 Class B private IPv4 address block boundaries.
The Class B private address range is 172.16.0.0 to 172.31.255.255 (with a /12 prefix length).
RFC 1918 reserves specific IPv4 address spaces for internal, non-globally routable enterprise networks.
2
Evaluate the candidate IPv4 addresses against the Class B boundary range.
172.20.15.5 has a second octet value of 20, which lies inclusively between 16 and 31.
Any IP address starting with 172.16.x.x through 172.31.x.x is part of the RFC 1918 Class B private allocation.

Key Concept

RFC 1918 Private IPv4 Addressing
Question 23Question →

Match each RFC 1918 private IPv4 address prefix block to its corresponding scope and address range definition.

Click a left item, then click its matching right item

Items

10.0.0.0/8
172.16.0.0/12
192.168.0.0/16

Matches

Show answer & explanation

Answer

10.0.0.0/8 matches a single Class A network block (10.0.0.0 - 10.255.255.255); 172.16.0.0/12 matches 16 contiguous Class B network blocks (172.16.0.0 - 172.31.255.255); 192.168.0.0/16 matches 256 contiguous Class C network blocks (192.168.0.0 - 192.168.255.255).
RFC 1918 explicitly defines three private address blocks: one Class A block (10.0.0.0/8), 16 contiguous Class B blocks (172.16.0.0/12, spanning 172.16.0.0 to 172.31.255.255), and 256 contiguous Class C blocks (192.168.0.0/16, spanning 192.168.0.0 to 192.168.255.255).

Step-by-Step Solution

1
Identify the RFC 1918 range and structure for Class A private addressing.
10.0.0.0/8 covers addresses from 10.0.0.0 through 10.255.255.255, representing a single Class A block.
RFC 1918 allocates one /8 block for Class A private networks.
2
Identify the RFC 1918 range and structure for Class B private addressing.
172.16.0.0/12 covers addresses from 172.16.0.0 through 172.31.255.255, forming 16 contiguous Class B (/16) blocks.
RFC 1918 allocates 16 contiguous /16 blocks starting at 172.16.0.0 up to 172.31.255.255.
3
Identify the RFC 1918 range and structure for Class C private addressing.
192.168.0.0/16 covers addresses from 192.168.0.0 through 192.168.255.255, forming 256 contiguous Class C (/24) blocks.
RFC 1918 allocates 256 contiguous /24 blocks starting at 192.168.0.0 up to 192.168.255.255.

Key Concept

RFC 1918 Private IPv4 Address Space Allocation
Question 24Question →

A network engineer is configuring an internal WLAN management interface on an enterprise wireless LAN controller. To comply with corporate security policy, the interface must be assigned an IPv4 address from the RFC 1918 private address space so that it is non-routable over the public Internet. Which of the following IPv4 addresses meets this requirement?

Show answer & explanation

Answer: 172.22.100.15

Answer

172.22.100.15 is the only address within the RFC 1918 private IPv4 specification.
The IPv4 address 172.22.100.15 belongs to the 172.16.0.0/12 block (range 172.16.0.0 – 172.31.255.255), which is explicitly reserved by RFC 1918 for private internal networking.

Step-by-Step Solution

1
Recall the defined RFC 1918 private IPv4 address blocks.
Class A: 10.0.0.0 to 10.255.255.255 (10.0.0.0/8); Class B: 172.16.0.0 to 172.31.255.255 (172.16.0.0/12); Class C: 192.168.0.0 to 192.168.255.255 (192.168.0.0/16).
RFC 1918 sets aside specific address ranges for internal private enterprise networks.
2
Compare each option against the RFC 1918 range limits.
172.22.100.15 has a second octet of 22, which is between 16 and 31.
Any address in the 172.16.0.0/12 block is a valid private IPv4 address.

Key Concept

RFC 1918 Private IPv4 Address Ranges
Estimated Time:1m 0s
PreviousPage 2 / 2
Private IPv4 Addressing and RFC 1918 Practice Questions — Cisco CCNA — Page 2 | Examkin