100-150 · domain
Addressing and Subnet Formats
This domain covers IPv4 and IPv6 addressing and subnetting: address classes, private ranges, subnet masks and prefixes, network, host and broadcast addresses, and subnet design from a given block. Cisco 100-150 questions ask you to compute broadcast addresses, pick valid subnet IDs, read interface configurations, and identify what a mask defines.
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What to know about Addressing and Subnet Formats
Be able to convert between prefix length and subnet mask, find network and broadcast addresses, and pick valid subnets inside a given block. The single most important thing is correctly identifying the network and host boundaries before computing any address.
Deriving network, host, and broadcast addresses from an IPv4 address and prefix such as 172.16.20.0/24.
Selecting valid subnet IDs when dividing a block like 10.50.0.0/16 into /24 segments.
Interpreting IPv6 interface configuration, including global unicast and link-local addressing, to judge router connectivity.
Explaining that the subnet mask separates the network portion of an IPv4 address from the host portion.
Why learners struggle
Why Addressing and Subnet Formats questions are commonly missed
Subnetting questions are missed when learners calculate the right subnet size but pick the wrong network address, forget to subtract network and broadcast addresses from usable hosts, or confuse the number of subnets with the number of hosts per subnet.
- ·Network and broadcast are not usable — subtract 2 from the host count for every subnet
- ·Block size — always a power of 2; 2^host-bits gives addresses per subnet
- ·Which subnet a host is in — divide the host octet by block size to find the network address
- ·Subnets vs hosts per subnet — different calculations that learners frequently swap
- ·CIDR prefix vs subnet mask — /24 = 255.255.255.0, /25 = 255.255.255.128
- ·A valid mask does not mean it meets the design requirement — check the host count
Watch out for
Common Addressing and Subnet Formats exam traps
- ▸Setting the broadcast address to the first address or the network address instead of the last address in the subnet.
- ▸Choosing subnet IDs that fall outside the parent block or overlap, or that are not aligned to the new prefix boundary.
- ▸Assuming an IPv6 interface is unreachable when only a link-local address is shown, or confusing link-local with global unicast.
Question index
All Addressing and Subnet Formats questions (43)
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A network administrator is configuring a point-to-point WAN link between two Cisco routers. To conserve IPv4 address space, the administrator decides to use a /30 subnet mask on the serial interface. Which of the following best describes the number of usable host addresses provided by this subnet mask?
Medium2Refer to the exhibit. An administrator is configuring subnets on a Cisco router. Based on the output, what is the broadcast address for the subnet connected to Gig0/0?
Hard3A network administrator is configuring a point-to-point link between two routers and wants to use the most efficient subnet mask that allows for only two usable host addresses. However, the administrator is told to use a /28 mask instead for future expansion. How many usable host addresses are provided by a /28 mask?
Hard4Which of the following is a Class C IP address?
Easy5What is the decimal equivalent of the subnet mask 255.255.255.224?
Easy6In an IPv6 environment, which address type is automatically configured on every IPv6-enabled interface and is used for neighbor discovery and router solicitation?
Medium7A network technician is configuring a small branch office network. The ISP has assigned a single public IPv4 address that must be shared by all internal devices. The technician needs a solution that allows multiple internal hosts to communicate on the internet simultaneously without requiring a one-to-one mapping of internal to external addresses. Which technology should the technician implement?
Medium8An engineer needs to subnet a 192.168.10.0/24 network to provide at least 5 usable subnets, with each subnet accommodating a minimum of 25 host devices. Which subnet mask meets these specific design requirements?
Medium9A host with the IP address 192.168.1.50 and a subnet mask of 255.255.255.0 is attempting to send data to a server at 10.1.1.5. Which address must be configured on the host to allow the data to exit the local subnet?
Easy10A network administrator is planning to deploy IPv6 on a Cisco router. The administrator needs to assign a global unicast address to the GigabitEthernet0/0 interface. Which of the following addresses is a valid global unicast IPv6 address that can be manually configured on the interface?
Hard11A small branch office has been assigned the network 192.168.50.0/24. The network administrator must divide it into four equal-sized subnets to match four separate departments. Which subnet mask should be configured on the router interfaces to create exactly four usable subnets?
Easy12Which IPv6 address type is represented by the prefix fe80::/10?
Easy13Refer to the exhibit. An administrator is reviewing the interface configuration. Which statement regarding these subnets is true?
Hard14Which TWO of the following statements correctly describe the characteristics of IPv4 address classes?
Medium15An organization is using Variable Length Subnet Masking (VLSM) to optimize their 10.0.0.0/24 space. They need one subnet for 100 hosts and two subnets for 50 hosts each. Which of the following set of subnets correctly fulfills this requirement without overlapping?
Hard16Which of the following is the correct representation of the IPv6 address 2001:0DB8:0000:0000:0008:0800:200C:417A in compressed format?
Medium17Which THREE fields are found in the standard IPv4 header and are directly related to the delivery or identification of the packet across subnets?
Medium18A network administrator is documenting the addressing scheme for a new subnet. The subnet uses the IPv4 address 192.168.100.0 with a prefix length of /26. How many usable host addresses are available in this subnet?
Easy19A network engineer is troubleshooting connectivity on a host configured with the address 10.10.10.130/26. The host cannot reach a server at 10.10.10.200. Assuming no ACLs or routing issues, what is the most likely explanation?
Hard20Which TWO of the following statements regarding IPv4 address types are true?
Medium21Refer to the exhibit. What is the maximum number of usable host IP addresses available on this subnet?
Hard22A network engineer is configuring a large subnet for a campus and uses the 172.16.0.0/23 prefix. What is the last usable host address available in this subnet?
Hard23What is the directed broadcast address for the subnet in which the host 172.16.50.131/29 resides?
Medium24A network administrator is subnetting the 172.16.0.0/22 network into smaller subnets to support point-to-point WAN links between routers. Each WAN link requires exactly two usable IP addresses. Which subnet mask should the administrator use to maximize the number of subnets while meeting the requirement?
Hard25A company uses the 172.16.0.0/16 private address block. The network architect needs to create subnets that each support at least 500 hosts while maximizing the number of subnets available. Which subnet mask should be chosen?
Medium26A network technician is tasked with dividing the 192.168.10.0/24 network into four equal-sized subnets to accommodate different departments. Which subnet mask should be applied to achieve this requirement, and how many usable host addresses will be available in each subnet?
Medium27An administrator needs to subnet the 192.168.10.0/24 network into subnets that support at least 25 hosts each. Which CIDR mask provides the most efficient use of addresses while meeting the requirement?
Medium28A network engineer is configuring IPv6 on a Cisco router interface. The engineer assigns the address 2001:db8:acad:1::1/64 to GigabitEthernet0/0. Which of the following statements is true regarding the interface's IPv6 configuration?
Hard29A network administrator is documenting the IPv6 addressing scheme for a new campus. The administrator must identify which statements about IPv6 address structure and notation are accurate. (Choose two.)
Hard30A network engineer needs to allocate a subnet for a link connecting two routers. Which prefix provides the most efficient addressing for a point-to-point connection?
Medium31An administrator needs to subnet the 192.168.10.0/24 network into subnets that can support at least 25 hosts each. Which subnet mask provides the maximum number of subnets while meeting the host requirement?
Medium32Which TWO of the following statements regarding IPv6 address representation are accurate?
Medium33What is the broadcast address for the network 172.16.20.0/24?
Medium34A network engineer is configuring IPv6 on a Cisco router interface. The engineer wants to ensure that the interface can automatically generate a link-local address and participate in neighbor discovery without manual configuration. Which IPv6 address type is automatically generated on the interface when IPv6 is enabled?
Medium35A small office technician is assigning IPv4 addresses to devices on a network that will not connect to the internet and uses the 192.168.50.0/24 range. The technician needs to pick an address from the valid host range for this network. Which address should the technician choose?
Easy36Which TWO statements correctly describe valid rules for compressing or representing IPv6 addresses?
Medium37Which THREE of the following are valid private IPv4 address ranges as defined in RFC 1918?
Medium38Which TWO of the following statements are true regarding IPv4 and IPv6 coexistence?
Hard39Refer to the exhibit. Based on the IPv6 configuration of the GigabitEthernet0/0 interface, which statement is true regarding the connectivity of this router?
Hard40Which component of an IPv4 address does the subnet mask identify?
Easy41A network technician is configuring a point-to-point serial link between two Cisco routers. To conserve address space, the engineer wants the smallest possible subnet that still provides two usable host addresses. Which subnet mask should be applied to the serial interfaces?
Medium42A network designer is planning to use the 10.50.0.0/16 address space. Which TWO of the following represent valid network IDs for subnets created by further dividing this space into /24 segments?
Hard43A network administrator is documenting a subnet used for a point-to-point WAN link between two Cisco routers. The link is configured with the address 10.10.10.1/30. What is the network address and the usable host range for this subnet?
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Frequently asked questions
- What does the Addressing and Subnet Formats domain cover on the 100-150 exam?
- Be able to convert between prefix length and subnet mask, find network and broadcast addresses, and pick valid subnets inside a given block. The single most important thing is correctly identifying the network and host boundaries before computing any address.
- How many questions are in this domain?
- This page lists all 43 Addressing and Subnet Formats questions in the 100-150 question bank. The actual exam draws from this domain proportionally to its weighting in the official exam blueprint.
- What is the best way to practise this domain?
- Start with a short focused session (10 questions) to identify gaps, then work through explanations. Repeat with a longer session once the weak areas feel solid.
- Can I practise only Addressing and Subnet Formats questions?
- Yes — the session launcher on this page filters questions to this domain only. Choose any session length for inline explanations and scoring.