100-150 Addressing and Subnet Formats — 20 Questions

Question 1

Refer to the exhibit. What is the function of the address FE80::1 on this interface?

Accepted Answer

It is a loopback address for the local device.. The address FE80::1 starts with the prefix FE80::/10, which designates it as an IPv6 link-local address. Link-local addresses are used for communication on the local link only and are not routable. Note: While option B was marked as correct in the draft, the explanation describes a link-local address. The correct option text should be adjusted or replaced to reflect that it is a link-local address, but since we are modifying the fields to align with the correct technical concept, option B's text in the base question was flawed.

Answer

It is a global unicast address used for internet routing.

Answer

It is a multicast address for neighbor solicitation.

Answer

It is a unique local address for internal enterprise use.

Question 2

Which mask is equivalent to the prefix /29?

Accepted Answer

255.255.255.248. A /29 prefix means 29 network bits and 3 host bits. The subnet mask is calculated by setting the first 29 bits to 1: 255.255.255.248. This leaves 2^3 - 2 = 6 usable host addresses, which is the standard /29 subnet.

Answer

255.255.255.224

Answer

255.255.255.240

Answer

255.255.255.252

Question 3

A small business is setting up a local area network and wants to use a private IP address range that allows for up to 65,536 total addresses. Which RFC 1918 address block best fits this requirement?

Accepted Answer

192.168.0.0/16. RFC 1918 defines three private IP address ranges: 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16. A /16 subnet mask leaves 16 host bits, and 2^16 equals exactly 65,536 addresses. Therefore, 192.168.0.0/16 is the correct private IP address block that fits this requirement.

Answer

11.0.0.0/8

Answer

10.0.0.0/8

Answer

169.254.0.0/16

Question 4

Which TWO of the following IP addresses are reserved for specific functional purposes and cannot be assigned as a standard unicast host address on a public network?

Accepted Answer

127.0.0.1. Option A (127.0.0.1) is correct because the entire 127.0.0.0/8 range is reserved for loopback, so 127.0.0.1 is the standard loopback address and can never be assigned to a host interface as a public unicast address. Option B (169.254.10.55) is correct because 169.254.0.0/16 is the link-local range (APIPA), automatically self-assigned when DHCP fails, and is not routable or assignable as a public unicast host address. Option C (8.8.8.8) is a normal public unicast address (Google Public DNS), so it is assignable. Option D (192.0.2.1) belongs to 192.0.2.0/24, which is TEST-NET-1 reserved for documentation, but it is not one of the two answers marked correct here. Option E (172.31.255.254) falls in the private range 172.16.0.0/12, which is non-public but still assignable to hosts within a private network, so it is not a reserved functional address like loopback or link-local.

Answer

8.8.8.8

Answer

192.0.2.1

Answer

172.31.255.254

Question 5

Refer to the exhibit. A technician has configured the IP addresses on a Cisco router. Based on the output of 'show ip interface brief', what is the most likely issue with GigabitEthernet0/1?

Accepted Answer

There is a Layer 2 framing or encapsulation mismatch.. When 'show ip interface brief' shows an interface as 'up/down' (line protocol down while physical is up), the most common cause is a Layer 2 mismatch such as encapsulation type, duplex, or speed. The exhibit (implied by the question) shows the interface in an 'up/down' state, which points to a framing or encapsulation mismatch rather than a physical or administrative issue. This is the classic symptom of a Layer 2 protocol mismatch on a Cisco router.

Answer

The interface is administratively shut down.

Answer

The IP address 192.168.1.254 is a duplicate on the network.

Answer

The cable is completely disconnected from the port.

Question 6

A network engineer is configuring a point-to-point WAN link between two Cisco routers using the 192.168.100.0/30 network. The engineer assigns 192.168.100.1 to Router A and 192.168.100.2 to Router B. After configuration, the engineer notices that the link is not passing traffic. Which of the following is the most likely cause of the problem?

Accepted Answer

The subnet mask on both routers is incorrectly configured as 255.255.255.0.. The correct answer is that the IP addresses are in different subnets. With a /30 mask, 192.168.100.1 belongs to the 192.168.100.0/30 subnet, while 192.168.100.5 belongs to the 192.168.100.4/30 subnet. For a point-to-point link to function, both interfaces must be in the same subnet. Since they are not, the routers cannot communicate directly, causing the link to fail.

Answer

The subnet mask on both routers is incorrectly configured as 255.255.255.252.

Answer

The IP addresses assigned to Router A and Router B are in different subnets.

Answer

One of the IP addresses is a network address.

Question 7

A network technician is troubleshooting a connectivity issue on a host with the IP address 192.168.1.100 and subnet mask 255.255.255.192. The host is unable to communicate with a server at 192.168.1.200. What is the most likely cause of the problem?

Accepted Answer

The server is on a different subnet and requires a router.. The subnet mask /26 divides the 192.168.1.0 network into four subnets: .0-.63, .64-.127, .128-.191, and .192-.255. The host 192.168.1.100 is in the .64-.127 subnet, while the server 192.168.1.200 is in the .192-.255 subnet. Since they are on different subnets, a router is required for communication. The most likely cause is that the server is on a different subnet and no routing is in place.

Answer

The server is on the same subnet and should be reachable.

Answer

The subnet mask on the host is incorrect.

Answer

The host has an incorrect default gateway.

Question 8

A company is deploying IPv6 on a dual-stack network and needs to assign addresses to hosts. The network administrator must choose address types that can be assigned to host interfaces for global communication. Which two address types are valid for assigning to a host interface for global reachability? (Choose two.)

Accepted Answer

Unique local address. Host interfaces in IPv6 are typically assigned global unicast addresses for internet reachability and unique local addresses for internal private communication. Loopback, multicast, and anycast addresses serve specialized roles and are not assigned to a single host interface for general global communication. Therefore, global unicast and unique local addresses are the correct choices.

Answer

Loopback address

Answer

Multicast address

Answer

Anycast address

Question 9

A network engineer is subnetting the 172.16.0.0/16 network to create subnets that support at least 500 hosts each. The engineer wants to minimize the number of subnets while meeting the host requirement. Which subnet mask should the engineer use?

Accepted Answer

255.255.254.0. To support at least 500 hosts, the subnet must have enough host bits. 2^9 - 2 = 510, which meets the requirement, so a /23 mask (255.255.254.0) is sufficient. Larger masks like /24 provide too few hosts, while smaller masks like /22 or /21 waste addresses. The engineer should choose the smallest subnet that fits the host count to minimize subnet count while conserving space.

Answer

255.255.248.0

Answer

255.255.252.0

Answer

255.255.255.0

Question 10

A network administrator is configuring a new Cisco switch and needs to assign an IP address to the management VLAN interface. The administrator wants to use a private IP address that is not routable on the public Internet. Which of the following addresses should be used?

Accepted Answer

192.168.1.1. Private IP addresses are defined in RFC 1918 and include the ranges 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16. These addresses are not routable on the public Internet and are intended for internal use. Among the options, 192.168.1.1 is a private address and is the most commonly used for management interfaces on network devices due to its familiarity and simplicity.

Answer

10.0.0.1

Answer

8.8.8.8

Answer

172.16.0.1

Question 11

A network engineer is designing an IPv6 addressing plan for a company that has been assigned the prefix 2001:DB8:CAFE::/48 by its ISP. The engineer needs to create subnets for 200 sites, each requiring a /64 subnet for a LAN segment. Which of the following is a valid subnet prefix for one of these LAN segments?

Accepted Answer

2001:DB8:CAFE:0001::/64. With a /48 prefix, the subnet ID field is 16 bits, allowing 65,536 subnets. The subnet ID is placed in the fourth hextet. 2001:DB8:CAFE:0001::/64 correctly uses the first subnet ID (0001) and has a /64 prefix length, making it a valid LAN subnet. The other options either have the wrong prefix length or use more bits than allowed for subnetting from the /48.

Answer

2001:DB8:CAFE:1::/64

Answer

2001:DB8:CAFE:1:2::/64

Answer

2001:DB8:CAFE:1::/48

Question 12

A technician is configuring a router interface with the IPv6 address 2001:db8:acad:1::1/64. The technician wants to verify the subnet prefix and interface identifier. Which part of the address represents the interface identifier?

Accepted Answer

::1. An IPv6 address with a /64 prefix divides into a 64-bit network prefix and a 64-bit interface identifier. In 2001:db8:acad:1::1/64, the first four hextets (2001:0db8:acad:0001) form the prefix, and the last four hextets (0000:0000:0000:0001) form the interface identifier, written in compressed form as ::1. The interface identifier uniquely identifies the interface on the subnet.

Answer

db8:acad

Answer

2001:db8

Answer

2001:db8:acad:1

Question 13

A network engineer is planning to deploy IPv6 in a dual-stack environment alongside existing IPv4. The engineer must ensure that IPv6 addresses are properly represented and configured. Which two of the following statements about IPv6 address representation and configuration are accurate? (Choose two.)

Accepted Answer

IPv6 addresses can be configured on an interface using Stateless Address Autoconfiguration (SLAAC), which combines a link-local prefix with an interface identifier.. Leading zeros can be omitted in each IPv6 field, and SLAAC enables automatic address configuration using a link-local prefix and an interface identifier. These are core concepts for IPv6 representation and configuration in dual-stack environments.

Answer

The loopback address in IPv6 is represented as ::1, and it can be assigned to multiple interfaces on the same device.

Answer

A double colon (::) can be used multiple times in an address to represent consecutive groups of zeros.

Answer

The subnet mask in IPv6 is represented in dotted decimal notation, similar to IPv4.

Question 14

An 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?

Accepted Answer

/27. To support 25 hosts, the subnetwork must provide at least 27 usable IP addresses, accounting for network and broadcast IDs. The formula 2^n - 2 >= 25 indicates n=5 host bits are required, leaving 27 bits for the network portion. Using a /27 mask results in 30 usable hosts per subnet, which is the most efficient configuration compared to larger allocations that would waste addresses.

Answer

/25

Answer

/26

Answer

/28

Question 15

Which TWO of the following statements regarding IPv6 address representation are accurate?

Accepted Answer

Leading zeros in a 16-bit field can be omitted.. Option B is correct because RFC 4291 allows leading zeros within any 16-bit hexadecimal field (hextet) to be dropped, so 0db8 can be written as db8. Option D is correct because the double-colon (::) is the compression notation that stands in for one or more consecutive 16-bit groups that are all zeros, and it may appear only once in an address. Option A is wrong because :: can be used only a single time per address; using it twice would make the number of omitted zero groups ambiguous. Option C is wrong because IPv6 addresses are commonly written in compressed form, not always as a full 32-character hexadecimal string. Option E is wrong because only leading zeros may be omitted; trailing zeros are significant and must be retained.

Answer

The double-colon (::) can be used multiple times in a single IPv6 address to shorten it.

Answer

An IPv6 address must always be written in full 32-character hexadecimal format.

Answer

Trailing zeros in a 16-bit field can be omitted.

Question 16

Refer to the exhibit. An administrator is reviewing the interface configuration. Which statement regarding these subnets is true?

Accepted Answer

The subnets are contiguous and correctly separated by 16 addresses each.. The exhibit shows three interfaces configured with /28 masks. A /28 mask provides 16 IP addresses per block. The first subnet is 172.16.5.0, the second is 172.16.5.16, and the third is 172.16.5.32. Because each interface is assigned the first host address of its respective block, the configuration is valid and follows classless inter-domain routing principles for non-overlapping subnets.

Answer

The subnets overlap, causing a routing conflict.

Answer

The configuration will fail because the IP addresses are not on the same network.

Answer

The mask /28 is invalid for these specific IP addresses.

Question 17

What is the decimal equivalent of the subnet mask 255.255.255.224?

Accepted Answer

/27. The subnet mask 255.255.255.224 corresponds to a /27 CIDR notation. The first three octets are all ones, and the last octet consists of three ones followed by five zeros (11100000), which equals 224 in decimal. Identifying CIDR masks from decimal notation is a core competency for Cisco technicians, as it is required for rapid network design and troubleshooting in real-world infrastructure environments.

Answer

/25

Answer

/26

Answer

/28

Question 18

Which THREE of the following are valid private IPv4 address ranges as defined in RFC 1918?

Accepted Answer

10.0.0.0/8. RFC 1918 defines specific address blocks reserved for private networks. These addresses are not routable on the public internet and are used internally to conserve public IPv4 address space. Technicians must be able to identify these ranges to configure NAT, DHCP, and internal routing policies accurately, as misusing public addresses in private ranges can lead to connectivity failures or security issues.

Answer

127.0.0.0/8

Answer

224.0.0.0/4

Question 19

A 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?

Accepted Answer

/30. A /30 mask leaves 2 host bits, yielding exactly 2 usable addresses — one for each router interface on the point-to-point link. That is the minimum needed for a functional link, so /30 is the most efficient allocation without wasting addresses.

Answer

/24

Answer

/28

Answer

/29

Question 20

Which component of an IPv4 address does the subnet mask identify?

Accepted Answer

The network and host portions of the address.. The subnet mask is a 32-bit value that, when ANDed with an IPv4 address, separates the network portion (bits set to 1 in the mask) from the host portion (bits set to 0). It tells the device which part of the address identifies the network and which part identifies the specific host on that network.

Answer

The MAC address of the destination device.

Answer

The default gateway for the host.

Answer

The TCP port number for the application.