Network Fundamentals CompTIA Network+

Several OSI model layers provide error detection services, but only one that provides error correction as well. At which layer of the OSI model is there a protocol that provides both end-to-end error detection and correction?

• Physical Layer

• Data Link Layer

• Network Layer

• Transport Layer

Answer explanation

D is correct because TCP, a connection-oriented transport layer protocol, performs its own error detection, but it also includes a packet acknowledgment service. The segments transmitted during a TCP connection are numbered, so the acknowledgment messages generated by the receiver can specify the number of the last packet received correctly. The sender processes these messages and automatically retransmits any unacknowledged packets.

Which of the following OSI model layers specifies the address of each packet’s sender and its ultimate recipient?

• Data Link Layer

• Network Layer

• Transport Layer

• Session Layer

Answer explanation

B is correct because IP, at the network layer, is the protocol responsible for end-to-end transmissions between the packet’s sender and its ultimate recipient. The IP header therefore contains IP addresses that identify the two end systems.

Ralph is consulting at a site with mixed networking technologies accumulated over many years. An assistant electrician working in the drop ceiling has informed Ralph that he accidentally severed one of the network cables running through the ceiling space. The electrician didn’t know what kind of network cable it was, which concerned Ralph because the site had installations using coaxial, fiber optic, and twisted pairs. The use of various topologies at the site meant that the effect of a single cable break could vary.

With which topology would the severed cable cause the greatest amount of disturbance to the network?

• Mesh

• Logical Ring

• Bus

• Star

Answer explanation

C. is correct because a severed cable in a bus topology would split the network into two halves. This would prevent the nodes on one side of the break from communicating with those on the other side. Both halves of the network would also have one cable end without a terminator, which could inhibit communication among the computers on the same side of the break.

Ralph is planning on a career in IT, and he wants to build a home LAN for learning purposes. Ralph has purchased three used PCs, and he has installed an Ethernet network interface adapter in each. He has also purchased three CAT 6 UTP patch cables. Ralph wants to use the star topology for his network, but he is unsure about what device to purchase for his cabling nexus, the center of the star.

Which of the following components will result in a LAN when Ralph plugs his three computers into it? (Select all correct answers.)

• Hub

• MAU

• Switch

• Router

Answer explanation

A is correct because a hub can function as the cabling nexus at the center of an Ethernet star topology. Each of the devices on the network is plugged into the hub, resulting in a LAN.

C is correct because a switch can function as the cabling nexus at the center of an Ethernet star topology. Each of the devices on the network is plugged into the switch, resulting in a LAN.

Your company has just purchased an office building that stands 300 meters away from the current building, and the IT director has assigned you the task of joining together the networks in the two buildings. The connection must support at least Gigabit Ethernet speed and be resistant to the electromagnetic interference generated by manufacturing equipment in the area.

The director also wants the solution to be as inexpensive as possible. Which of the following cable types should you use to connect the buildings?

• RG-58 coaxial cable

• CAT 6 unshielded twisted pair (UTP)

• CAT 8 shielded twisted pair (STP)

• Multimode fiber-optic

• Single-mode

  fiber-optic

Answer explanation

D is correct because multimode fiber-optic cable can support both the 300 meter distance and the Gigabit Ethernet speed and is the most inexpensive option that meets both requirements.

Which of the following IEEE twisted pair cable categories calls for shielded twisted pair (STP) instead of unshielded twisted pair (UTP) cable?

• CAT 5e

• CAT 6

• CAT 6a

• CAT 8

Answer explanation

D is correct because achieving the extremely high transmission speeds of 40GBase-T, even over short distances, required shielding around the individual wire pairs and around the whole bundle, to provide additional protection against crosstalk and other types of interference.

Alice has been directed by her supervisor to take a Class B network address and devise a plan to subnet it by creating 60 subnets supporting up to 1,000 hosts on each one. Alice has calculated that she needs 6 address bits to support 60 subnets and 10 bits to support 1,000 hosts, but she is unsure about how to go about allocating the bits.

Which of the following best describes how Alice should manipulate the address she has been given to create a subnet identifier?

• Extend the network identifier by 6 bits and the host identifier by 10 bits.

• Borrow 6 bits from the existing host identifier.

• Borrow 6 bits from the existing network identifier.

• Borrow 6 bits from the existing network identifier and 10 bits from the host identifier.

  Practice Question

Answer explanation

B is correct because borrowing 6 bits from the network identifier for a subnet identifier allows the creation of up to 64 subnets and leaves 10 bits for a host identifier, which can support up to 1,024 hosts.

Ralph has been asked to design an IPv4 network on which he can create 10 subnets supporting up to 2,000 hosts on each.

Which of the following network addresses could Ralph use to create such a network?

• 192.168.43.0/27

• 172.16.96.0/21

• 10.128.0.0/10

• 127.223.0.0/16

Answer explanation

B is correct because the network address has a 5-bit subnet identifier, supporting up to 32 subnets, leaving 11 bits for the host identifier, which can support up to 2,046 hosts.

At the transport layer of the OSI model, all application traffic is handled by two protocols: TCP and UDP. Of the two, UDP is understood to have a significantly smaller bandwidth overhead than TCP.

Which of the following factors in UDP contribute to its reduced overhead? (Choose all correct answers.)

• No checksum

• No three-way

  handshake

• Lower port numbers

• Smaller header

Answer explanation

B is correct because TCP, a connected-oriented protocol, requires additional messages for connection establishment, whereas UDP, a connectionless protocol, does not.

Ralph is building a new network for a client and has just installed a DHCP server with a scope containing an entire /24 subnet: 254 addresses. There are to be 100 workstations in the office, and Ralph has figured that the 254 addresses will be enough to accommodate them plus the users’ mobile phones and other Wi-Fi devices. Sometime later, Ralph began receiving complaints from his client that users sometimes could not connect to the network.

Ralph examines the DHCP server and notices that the scope, at that moment, had only two available leases. He concludes that the scope has been exhausted at times, preventing any more users from connecting to the network. When some of the existing leases expire, more addresses become available. Ralph’s client explains that their business gets a lot of visitors who use the company's Wi-Fi on their phones, which helps to explain the address shortage. Ralph wants to avoid having to add more addresses to the network.

What can he do to relieve the occasional address shortages on his client’s network?

• Install a second DHCP server

• Create a second scope on the DHCP server

• Decrease the lease period for the scope

• Increase the lease period for the scope

Answer explanation

C is correct because decreasing the lease period for the scope will cause addresses to be returned to the pool for reassignment more quickly.