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A company wants private IPv4 addressing that can be routed internally but not on the public Internet. Which range meets that requirement?

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A company wants private IPv4 addressing that can be routed internally but not on the public Internet. Which range meets that requirement?

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Answer choices

Why each option matters

Good practice is not just finding the correct option. The wrong answers often show the exact trap the exam wants you to fall into.

A

Distractor review

198.51.100.0/24

This is a documentation range, not an RFC 1918 private range.

B

Best answer

172.20.0.0/16

Correct. It falls within the private 172.16.0.0/12 block.

C

Distractor review

169.254.0.0/16

That is link-local APIPA space, not general private addressing for routed design.

D

Distractor review

224.0.0.0/4

That is multicast space.

Common exam trap

Common exam trap: answer the scenario, not the keyword

A common exam trap is mistaking link-local (169.254.0.0/16) or documentation ranges (198.51.100.0/24) for private IP addresses. Link-local addresses are automatically assigned when DHCP fails and are not routable beyond the local segment, making them unsuitable for internal routed networks. Documentation ranges are reserved for examples and cannot be used for actual network addressing. Another trap is confusing multicast addresses (224.0.0.0/4) with private addresses; multicast is for group communication and cannot be assigned to hosts. Selecting these incorrect ranges leads to routing failures and violates RFC 1918 rules.

Technical deep dive

How to think about this question

Private IPv4 addressing is defined by RFC 1918 to provide IP address ranges that organizations can use internally without conflicting with public Internet addresses. These private addresses are routable within an organization's internal network but are not routable on the public Internet, ensuring internal communication while preserving global address uniqueness. The three main private IPv4 blocks are 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16, each offering different address space sizes for various network scales. The decision to select 172.20.0.0/16 as a private address range follows the rule that any IP within 172.16.0.0 to 172.31.255.255 is reserved for private use. This range is part of the 172.16.0.0/12 block, which includes addresses from 172.16.0.0 to 172.31.255.255. Cisco devices and routing protocols recognize these addresses as private, allowing internal routing without leaking to the public Internet. Using this range enables internal routing protocols like OSPF or EIGRP to operate normally without IP conflicts. A common exam trap is confusing private address ranges with other special-use IP blocks such as link-local (169.254.0.0/16), multicast (224.0.0.0/4), or documentation/test ranges (198.51.100.0/24). These are not suitable for internal routing or private addressing. For example, 169.254.0.0/16 is used for Automatic Private IP Addressing (APIPA) and is not routable. Understanding these distinctions helps avoid selecting incorrect ranges that would break internal routing or cause addressing conflicts.

KKey Concepts to Remember

  • RFC 1918 defines three private IPv4 address blocks that are routable internally but not on the public Internet.
  • The 172.16.0.0/12 block includes addresses from 172.16.0.0 to 172.31.255.255 and is valid for private internal routing.
  • Private IP addresses enable internal routing protocols like OSPF and EIGRP to function without IP conflicts on the public Internet.
  • Link-local addresses (169.254.0.0/16) are used for automatic IP assignment and are not routable beyond the local link.
  • Multicast address ranges (224.0.0.0/4) are reserved for group communication and cannot be used for private host addressing.
  • Documentation IP ranges such as 198.51.100.0/24 are reserved for examples and testing, not for private internal routing.
  • Selecting an IP range outside RFC 1918 private blocks can cause routing issues and IP conflicts with public Internet addresses.
  • Cisco devices recognize RFC 1918 addresses as private and typically require NAT to communicate with public networks.

TExam Day Tips

  • Watch for words such as best, first, most likely and least administrative effort.
  • Review why wrong options are wrong, not only why the correct option is correct.

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More questions from this exam

Keep practising from the same exam bank, or move into a focused topic page if this question exposed a weak area.

Question 1

A router learns the same prefix from both OSPF and EIGRP. Which route is installed by default?

Question 2

A router shows this output: R1#show ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 10.1.1.2 1 FULL/DR 00:00:34 192.168.12.2 GigabitEthernet0/0 10.1.1.3 1 2WAY/DROTHER 00:00:39 192.168.12.3 GigabitEthernet0/0 Which statement is correct?

Question 3

What is the OSPF metric called?

Question 4

A non-root switch has two uplinks toward the root bridge. One path has a lower total STP cost than the other. What role will the lower-cost uplink have?

Question 5

A router interface applies this ACL inbound: 10 deny tcp any any eq 80 20 permit ip any any A user reports that web browsing to a server by IP address fails, but ping works. Which statement best explains the behavior?

Question 6

A router learns route 198.51.100.0/24 from OSPF with AD 110 and also has a static route to the same prefix configured with AD 150. Which route is installed?

FAQ

Questions learners often ask

What does this 200-301 question test?

RFC 1918 defines three private IPv4 address blocks that are routable internally but not on the public Internet.

What is the correct answer to this question?

The correct answer is: 172.20.0.0/16 — RFC 1918 private addressing includes 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16.

What should I do if I get this 200-301 question wrong?

Then try more questions from the same exam bank and focus on understanding why the wrong options are tempting.

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