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1.0 Network Infrastructure and Connectivity

IPv4 Addressing Troubleshooting Practice Questions

Updated for CCNA v2.0

Subnet boundaries, gateways, duplicate and overlapping addressing, and public versus private ranges.

CCNA v2.0 objective 1.3 · objective map

Author-reviewed by LabFabric · 25 September 2026 · Report a content issue

One solved question, so you can see how these are marked

Which address ranges are private under RFC 1918?

10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16

The 172 range is only 172.16.0.0 to 172.31.255.255. 169.254.0.0/16 is link-local, 127.0.0.0/8 is loopback, and the 192.0.2.0 style ranges are documentation.

Every question in the set below is marked like this. The answers stay hidden until you pick one.

Find related practice in the CCNA path
Practise subnetting hands-onSee the 32 bits, split blocks into subnets, drill the 128/64/32/16/8/4/2/1 ladder, and practise the hex behind IPv6 (compression, prefixes, EUI-64). Free, in your browser.Open subnetting practice
All 8 IPv4 Addressing Troubleshooting questions in this set

Answers and explanations appear when you work through the set above.

  1. A host is configured 192.168.10.130/26. What are its network and broadcast addresses?

    • 192.168.10.128 and 192.168.10.191
    • 192.168.10.0 and 192.168.10.255
    • 192.168.10.128 and 192.168.10.255
    • 192.168.10.129 and 192.168.10.190

  2. A host at 10.1.1.200/25 is given a default gateway of 10.1.1.1. It cannot reach other networks. Why?

    • The gateway is in a different /25 subnet than the host
    • The gateway address ends in .1
    • The host is using a private address
    • The mask should be 255.255.255.255

  3. Two hosts on the same LAN show intermittent connectivity and both logged 'duplicate IP address' warnings. What is the most likely cause?

    • Two devices are configured with the same IPv4 address
    • The switch is running Rapid PVST+
    • The router has OSPF enabled
    • The DNS server is unreachable

  4. How many usable host addresses are in a /27 subnet?

    • 30
    • 32
    • 62
    • 14

  5. Which mask is commonly used for a point-to-point router link to conserve addresses?

    • /30, or /31 where supported
    • /24
    • /16
    • /8

  6. An engineer plans two subnets, 192.168.1.0/25 and 192.168.1.64/26, on different VLANs. What is the problem?

    • The subnets overlap, since 192.168.1.64/26 falls inside 192.168.1.0/25
    • Both subnets are public addresses
    • A /26 cannot be used with a /25
    • There is no problem

  7. Why do hosts with private addresses need NAT to communicate with servers on the internet?

    • Private addresses are not routable on the public internet
    • Private addresses cannot be used with TCP
    • Private addresses are always blocked by ARP
    • Private addresses cannot be subnetted

  8. Which command shows the IPv4 address and up/down status of every interface on a router in one summary?

    • show ip interface brief
    • show interfaces status
    • show ip protocols
    • show version