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1.0 Network Infrastructure and Connectivity

Subnetting Practice Questions

VLSM, subnet math, and host/network calculations.

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

How many usable host addresses does a /27 subnet provide?

30

A /27 leaves 5 host bits, giving 32 total addresses. Subtracting the network and broadcast addresses leaves 30 usable host addresses.

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 9 Subnetting questions in this set

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

  1. What is the subnet mask for a /20 network in dotted decimal?

    • 255.255.240.0 (20 network bits)
    • 255.255.224.0 (19 network bits)
    • 255.255.248.0 (21 network bits)
    • 255.255.192.0 (18 network bits)

  2. Given the network 192.168.10.64/26, what is the broadcast address?

    • 192.168.10.127
    • 192.168.10.95 (end of a /27 block)
    • 192.168.10.126 (last usable host)
    • 192.168.10.191

  3. A network engineer needs at least 500 usable IPv4 host addresses on a single subnet. Which prefix gives the smallest address block that satisfies this requirement?

    • /23 (510 usable hosts)
    • /24 (254 usable hosts)
    • /22 (1022 usable hosts)
    • /25 (126 usable hosts)

  4. What is the wildcard mask that corresponds to a /28 subnet mask, as would be used in an access control list or OSPF network statement?

    • 0.0.0.15
    • 0.0.0.31 (five wildcard bits)
    • 0.0.0.7
    • 0.0.0.255

  5. An address of 172.16.50.10 with a /21 mask belongs to which subnet?

    • 172.16.48.0/21
    • 172.16.50.0/21 (using the third octet unchanged)
    • 172.16.40.0/21 (the preceding /21 block)
    • 172.16.56.0/21 (the following /21 block)

  6. A company needs to subnet 10.10.0.0/16 using VLSM to support one subnet of 500 hosts, one of 100 hosts, and one of 20 hosts, all as small as possible. Which prefix length correctly fits the 100-host subnet?

    • /25 (126 hosts)
    • /24 (254 hosts)
    • /26 (62 hosts)
    • /23 (510 hosts)

  7. Which of the following correctly identifies the first usable host address in the subnet 192.168.5.32/28?

    • 192.168.5.33 (first usable host)
    • 192.168.5.32
    • 192.168.5.34 (second usable host)
    • 192.168.5.31

  8. A router interface is configured with IP address 10.20.30.65 and mask 255.255.255.192. Which subnet does this address belong to?

    • 10.20.30.64/26
    • 10.20.30.0/26
    • 10.20.30.128/26 (the next /26 block)
    • 10.20.30.32/26

  9. Two routers supporting RFC 3021 use a point-to-point IPv4 link needing exactly two endpoint addresses. Which prefix uses the fewest addresses?

    • /30 (4 addresses)
    • /29 (8 addresses)
    • /28 (16 addresses)
    • /31 (2 addresses)