Network+ Study Guide 2022
What type of addressing delivers a packet to a single host from a group without using unicast?
Anycast means that a group of hosts are configured with the same IP address. When a router forwards a packet to an anycast group, it uses a prioritization algorithm and metrics to select the host that is "closest" (that will receive the packet and be able to process it the most quickly).
A network designer wants to run a 10 gigabit backbone between two switches in buildings that are 75 m (246 feet) apart. What is the main consideration when selecting an appropriate copper cable?
At that distance, some type of shielded or screened cat 6A or better cable is required for the installation to be compliant with Ethernet standard 10GBASE-T.
How is the decimal value 12 expressed in hex?
C (this might be written 0xC for clarity). Values above 9 are expressed as letters (10=A, 11=B, 12=C).
Which categories of U/UTP cable are certified to carry data transmission faster than 100 Mbps?
Cat 5e and Cat 6/6A. Cat 7 and Cat 8 are screened/shielded types.
Users on a floor served by a single switch cannot get a network connection. What is the best first step?
Check that the switch is powered on and reset it. If that does not work, check for other causes such as a poorly seated plug-in module.
Which OSI layer packages bits of data from the Physical layer into frames?
Data Link.
What is an EUI-64, and how might it be used by IPv6?
Extended unique identifier (EUI) is IEEE's preferred term for a MAC address. EUI-64 is a 64-bit hardware interface ID. A 48-bit MAC address can be converted to an EUI-64 by using a simple mechanism. The EUI-64 can be used as the IPv6 interface ID, though a randomly generated token is often preferred.
True or False? The IP address 172.24.0.1 is routable over the Internet.
False. 172.16.0.0—172.31.255.255 is the Class B private address range.
True or false? 6to4 is a dual stack method of transitioning from IPv4 to IPv6.
False. 6to4 is a method of tunneling IPv6 packets over an IPv4 network. Dual stack means that hosts and routers process both IPv4 and IPv6 traffic simultaneously.
True or False? Devices can only transmit on an Ethernet network when the media is clear, and the opportunity to transmit becomes less frequent as more devices are added. Also, the probability of collisions increases. These problems can be overcome by installing a hub.
False. The description of the problem is true, but the solution is not. This issue is resolved by using a bridge or (more likely these days) a switch
True or False? Cat standards apply only to wiring.
False—Connectors and interconnects are also rated to cat standards.
What is an MTU?
Maximum transmission unit—the maximum amount of data that a frame can carry as payload.
How would you test for excessive attenuation in a network link?
Measure the insertion loss in dB by using a cable tester.
You have selected an SFP+ 1310 nm Tx and 1490 nm Rx transceiver to implement a BiDi link between two switches. Should you provision a second SFP+ 1310 nm Tx and 1490 nm Rx for the other switch?
No, you need an SFP+ module with 1490 nm Tx and 1310 nm Rx.
What is a Class D address?
One used for multicasting.
Why is plenum-rated cable used when cable is run in an area where building air is circulated?
Plenum-rated cable produces minimal amounts of smoke if burned, must be self-extinguishing, and must meet other strict fire safety standards.
With CSMA/CD, what will happen if a host has data to transmit and there is already data on the cable?
The host will wait for a random backoff period before attempting to transmit again.
What are the characteristics of S/FTP cable?
This is a twisted pair type of copper cable using a braided outer screen and foil shielding for each pair to reduce interference.
Given an 18-bit netmask, are the IP addresses 172.16.1.10 and 172.16.54.10 on the same network?
Yes. Convert the IP addresses to binary, and you will see that the first 18 binary digits in each address are the same (10101100 00011110 00).
You need to verify whether a switch port is misconfigured by checking the number of collisions being reported. What general command could you use at a CLI to report this information?
show interface
Write the command to use tcpdump to capture traffic from the IP address 172.16.16.254 on the interface eth0 and output the results to the file router.pcap.
tcpdump -i eth0 -w 'router.pcap' src host 172.16.16.254
If a host is configured with the IP address 10.0.10.22 and mask 255.255.255.192, what is the broadcast address of the subnet?
10.0.10.63. Convert the IP address to binary (00001010 00000000 00001010 00010110), then work out the number of bits in the mask (26). Change the remaining host bits (6) to 1s and convert back to dotted decimal.
What type of fiber optic cable is suited for long distance links?
Single mode fiber (SMF).
You have connected a computer to a network port and cannot get a link. You have tested the adapter and cable and can confirm that there are no problems. No other users are experiencing problems. The old computer also experienced no problems. What cause would you suspect, and what is a possible next step?
Speed mismatch—Check the autonegotiate settings on the adapter and port.
If a packet is addressed to a remote network, what destination MAC address will the sending node use to encapsulate the IP packet in a frame?
The MAC address of the default gateway.
Which step follows "Implement the solution or escalate as necessary" in the troubleshooting methodology?
Verify full system functionality, and if applicable, implement preventive measures.
A server has a four-port gigabit Ethernet card. If a switch supports port aggregation, what bandwidth link can be achieved?
4 x 1 gigabit or 4 gigabit.
What maximum distance is defined in standards documentation for 1000BASE-LX running over MMF?
550 m (1804 feet). Note that 1000BASE-LX can run over MMF or SMF. SMF has much higher range.
A host is configured with the IP address 10.0.10.22 and subnet mask 255.255.255.192. How many hosts per subnet would this addressing scheme support?
62. Either subtract the least significant octet from 256 (256-192=64), then subtract 2 for the network and broadcast addresses, or having worked out that there are 6 host bits, calculate 26-2.
In IPv6, how is the loopback address best expressed?
::1
What type of address is used by the switch to forward transmissions to the appropriate host?
A media access control (MAC) address. This is a layer 2 address. It is also referred to as a hardware or physical address
Which step has been omitted from the following list of activities related to identifying the problem? Gather information • Duplicate the problem, if possible • Question users • Identify symptoms • Determine if anything has changed
Approach multiple problems individually.
What is an I/G bit?
Determines whether a frame is addressed to an individual node (0) or group (1). The latter is used for multicast and broadcast.
True or false? The DHCP server in the SOHO router assigns an IP address to the WAN interface automatically.
False—the DHCP server in the SOHO router assigns IP addresses to the hosts on the local network. The WAN address is likely to be assigned by DHCP, but a DHCP server is managed by the access provider.
Which factors are used by default in EIGRP to identify the least-cost path?
The lowest bandwidth link along the path and the sum of latency along the path.
You need to run UTP cable between two switches at opposite ends of a warehouse that is 140 m (459 feet) long. What additional device (if any) is required for the installation to be compliant with 1000BASE-TX Ethernet standard?
The maximum link length is 100 m (328 feet) so a repeater will be needed.
True or False? VLSM means using more than one mask to subnet an IP network.
True. By using different mask sizes, variable length subnet masking (VLSM) allows designers to match subnet sizes to requirements more precisely.
Convert the decimal value 72 into binary.
Work out the binary place positions that add up to 72: 128*0 + 64*1 + 32*0 + 16*0 + 8*1 + 4*0 + 2*0 + 1*0. Transcribe the 0s and 1s to form an octet: 01001000.
Which Ethernet standard works at 100 Mbps over Cat 5 or better copper cable?
100BASE-TX.
At which layer of the OSI model is no header encapsulation applied?
Physical.
How is the decimal value 171 expressed in hex?
0xAB. To work this out, divide 171 by 16 (144) and write the remainder (11) as the least significant hex digit (B). Note that the quotient 10 (the integer part of the sum, where 171/16=10.6875) is less than 16. Convert the quotient to hex (10=A) to derive the second hex digit and complete the conversion.
If the network ID is 10.1.0.0/22, how many IP addresses are available for allocation to host interfaces?
1,022. With a 22-bit mask, from the 32-bit IP address, there are 10 bits left for host addressing (32-22). 2 to the power 10 (210) is 1,024. You then need to subtract two for the network and broadcast addresses, which cannot be assigned to host interfaces.
At the 515support branch office, you have been asked to implement an IP network. Your network ID is currently 198.51.100.0/24. You need to divide this in half (two subnets) to accommodate hosts on two separate floors of the building, each of which is served by managed switches. The whole network is served by a single router. 1. To divide the network in half, what subnet mask do you need to use? 2. What are the subnet IDs for each network? 3. What is the broadcast address for each subnet? 198.52.100.127 and 198.51.100.255. 4. What is the range of assignable IP addresses for each subnet? 5. Your manager has considered his original plan and realized that it does not accommodate the need for a WAN link to the head office or a separate segment for a team that works with sensitive data. What mask will you need to accommodate this new requirement, and how many hosts per subnet will it allow?
1. Adding a single bit to the mask creates two subnets. The mask and network prefix will be 255.255.255.128 (/25). 2. 198.51.100.0 /25 and 198.51.100.128 /25. An easy way to find the first subnet ID is to deduct the least significant octet in the mask (128 in the example) from 256, giving the answer 128. 3. You can work these out quite simply from the subnet ID that you calculated. The broadcast address for the first subnet is 1 less than the next subnet ID. The second subnet's broadcast address is the last possible address. 4. 198.51.100.1 to 126 and 198.51.100.129 to 254. If you have each subnet ID and the broadcast ID, the host ranges are simply the values in between. 5. You now need four subnets: a /28 prefix or 255.255.255.240 mask. There are only 4 bits left to work with for host addressing, though, so there are just 14 host addresses per subnet.
If the IP address 10.0.10.22 were used with an /18 mask, how many subnets and hosts per subnet would be available?
1024 subnets each with 16,382 hosts. From the default mask, 10 bits are allocated to the subnet ID and 14 remain as host bits.
Which fiber Ethernet standard is best suited to implementing backbone cabling that does not exceed 200 m (656 feet) and can achieve at least 4 Gbps throughput?
10GBASE-SR.
Which types of distribution frame are best suited to 100 MHz or better operation?
110, BIX, and Krone blocks.
Which of the parameters in the following routing table entry represents the gateway? R 192.168.1.0/24 [120/1] via 198.51.100.254, GigabitEthernet0/1
198.51.100.254—the gateway is the address of the next hop router. 192.168.1.0/24 is the destination and GigabitEthernet0/1 is the interface that the packet should be forwarded out of to reach the gateway.
What type of distribution frame is best suited to cabling wall ports to Ethernet switches in way that best supports futures changes?
A patch panel allows wall ports to be connected to switches via patch cords. If a switch is replaced or if a wall port needs to be connected to a different switch port, the change can be made easily by moving a patch cord.
What tool is used to terminate wiring at a 110 block?
A punchdown tool is used to connect wires via insulation displacement connectors (IDCs). You must use a suitable blade for the IDC format (110, Krone, or BIX).
What component performs signal amplification to extend the maximum allowable distance for a media type?
A repeater.
At what layer of the OSI model does a fiber distribution panel work?
All types of distribution frames work at the physical layer (layer 1).
What is the measurement standard for wire thickness?
American Wire Gauge (AWG).
What is the dotted decimal representation of an 8-bit netmask?
An 8-bit mask means that each digit in the first octet is set to 1. Converted to dotted decimal, this becomes 255.0.0.0.
What is an ASN and how does it assist route aggregation?
An Autonomous System Number (ASN) identifies a group of network prefixes under the administrative control of a single entity (such as an ISP). The AS can be advertised to other ASs through a single prefix (route aggregation), hiding the complexity of the internal network from other autonomous systems.
What is a directly connected route?
An IP network or subnet connected to one of the router's interfaces.
Which cable type consists of a single core made of solid copper surrounded by insulation, a braided metal shielding, and an outer cover?
Coax.
True or False? A computer with a 10BASE-T Ethernet adapter cannot be joined to a 100BASE-T network
False. Fast Ethernet is backwards-compatible with 10BASE-T (and Gigabit Ethernet is backwards-compatible with Fast Ethernet).
True or false? A bridge does not forward broadcast traffic.
False. Segments on different bridge ports are in separate collision domains but the same broadcast domain.
True or False? The CRC mechanism in Ethernet allows for the retransmission of damaged frames.
False. The CRC indicates only that a frame may be corrupt.
True or False? The Session layer is responsible for passing data to the Network layer at the lower bound and the Presentation layer at the upper bound.
False. The Session layer is between the Transport and Presentation layers.
True or False? Documentation should be created only at the end of the troubleshooting process.
False. The last step of the methodology is to ensure that findings, actions, and outcomes are documented, but you cannot do this effectively without existing notes. Most troubleshooting takes place within a ticket system. Ideally, a documented job ticket would be opened at the start of recording the incident.
True or False? The arp utility will always show another host's MAC address if that host is on the same subnet.
False. While that is the function of the Address Resolution Protocol, the arp utility is used to inspect the ARP table cache, which may or may not contain the other host's address. Note that a standard means to ensure the MAC address is cached is to ping the destination address first. This is the basis of a utility called arping.
True or false? The WAN port on a SOHO router is connected to the LAN ports by an internal switch
False—the LAN ports and access point are connected by a switch. The WAN port is separate. Packets must be routed between the LAN and WAN segments.
Which copper Ethernet standard meets the bandwidth requirements for clients in an office network while minimizing costs?
Gigabit Ethernet. Provisioning 10 GbE would require upgrading the network adapters in most client devices, as well as potentially requiring upgraded cable installation.
You need to provision a fiber patch panel to terminate incoming cabling with green LC connectors. What type of ports should be provisioned on the patch panel?
Green connector color-coding indicates angled physical contact (APC) finishing. This type of finishing is incompatible with PC or UPC ports. The patch panel must be provisioned with Lucent Connector ports with APC finishing type.
100BASE-T transmit pins are 1 and 2. What color code are the wires terminated to these pins under T568A and T568B?
Green/White (pin 1) and Green (pin 2) for T658A or Orange (pin 1)/White and Orange (pin 2) for T568B.
What port configuration feature allows a server to smooth incoming traffic rates?
IEEE 802.3x flow control.
What output would you expect when running the command ip neigh?
IP:MAC address mappings held in the ARP cache of a Linux host.
Your network uses UTP cable throughout the building. There are a few users who complain of intermittent network connectivity problems. You cannot determine a pattern for these problems that relates to network usage. You visit the users' workstations and find that they are all located close to an elevator shaft. What is a likely cause of the intermittent connectivity problems? How might you correct the problem?
If the cabling is being run too close to the elevator equipment, when the elevator motor activates, it produces interference on the network wire. You can replace the UTP cable with screened/shielded copper wire or reposition the cables away from the elevator shaft.
When should you escalate a problem?
If you cannot solve it yourself (although it won't be good for your career if you give up too easily). You might also escalate if you do not have authorization to perform the necessary changes or if the system is under some sort of warranty.
A company has eight networks, using the subnet addresses 192.168.0.0/24, 192.168.1.0/24 ... 192.168.7.0/24. What network prefix and subnet mask can be used to summarize a supernet route to these networks?
It takes 3 bits to summarize eight networks (23 =8). Subtracting 3 bits from the existing network mask makes the supernet network prefix /21. The third octet of the mask will use 5 bits, which is 248 in decimal (25= 248), so the full mask is 255.255.248.0.
Given the subnet mask 255.255.255.128, are the IP addresses 192.168.0.1 and 192.168.1.1 on the same network?
No. Compare the decimal mask and dotted decimal IP addresses and note that the third octet is within the network portion but is different for each IP address. If you do convert to binary to check, remember that the subnet mask contains 25 bits. You can see that the 24th bit is different in each address. As that bit occurs within the netmask, the hosts are on different IP networks.
Which grade or grades of fiber have a 62.5 micron core?
OM1.
How can you check the IP configuration of an interface on an end system host at the command line?
On Windows, run ipconfig (or netsh interface ip show config or Get-NetIPAddress). On Linux, run ifconfig or ip a.
What cabling faults would a wire map tester detect?
Opens, shorts, and transpositions (reversed and crossed pairs).
A workstation cannot connect to a server application on a remote network. What is the first test you could perform to establish whether the workstation's link is OK?
Ping another local system, such as the default gateway.
A technician configures a switch port with a list of approved MAC addresses. What type of feature has been enabled?
Port security.
What is the reason for making power sum crosstalk measurements when testing a link?
Power sum crosstalk measures cable performance when all four pairs are used, as Gigabit and 10G Ethernet do.
Output from a ping command reports some values in milliseconds. What does this measure?
Round Trip Time (RTT) is a measure of the latency or delay between the host sending the probe and receiving a reply. ping will report minimum, maximum, and average RTT values.
Of the routing protocols listed in the CompTIA Network+ syllabus, which has the highest default value AD and does that make it more or less trusted than other protocols?
Routing Information Protocol (RIP) has a default administrative distance (AD) value of 120. In AD, lower values are preferred, so RIP is less trusted than other protocols.
In IPv6, how can a host obtain a routable IPv6 address without requiring manual configuration?
Stateless address autoconfiguration (SLAAC) allows a host to autoconfigure an interface by listening for Router Advertisements to obtain a network prefix.
A technician is troubleshooting a network and has asked your advice. He is trying to ping 192.168.16.192. The network has been subnetted with the custom mask 255.255.255.224. Why might this return a "Destination host unreachable" message?
The IP address resolves to the subnet network address, not a host address. Windows does not normally allow pinging the network address. Other OSs treat it as an alternative broadcast address, but most systems are configured to disallow such directed broadcasts for security reasons.
What function or service prevents an Internet host from accessing servers on the LAN without authorization?
The firewall.
What is the dotted decimal representation of an 18-bit netmask?
The first two octets take up 16 bits. In the third octet, the first two bits are set to one. In decimal, this is 192 (128+64). Therefore, the full mask is 255.255.192.0.
An IP network comprises hundreds of subnets deployed to offices in multiple geographical locations. Of the routing protocols listed in the CompTIA Network+ syllabus, which is best suited to this scale of network and why?
The hierarchical design of Open Shortest Path First (OSPF) means that it can divide the network into areas to represent different sites, reduce the size of routing tables, and ensure fast convergence. That said, Enhanced Interior Gateway Routing Protocol (EIGRP) can also support large networks and can have better convergence performance and so could be an equally good choice. Routing Information Protocol (RIP) is too limited to meet the requirements of a large network. Border Gateway Protocol (BGP) is not typically used on private networks as it is slower than OSPF or EIGRP and relative complex to configure.
You have pinged the router for the local subnet and confirmed that there is a valid link. The local host cannot access remote hosts, however. No other users are experiencing problems. What do you think is the cause?
The router is not configured as the default gateway for the local host. You can ping it, but the host is not using it for routing.
On a switched network, what configuration changes must be made to allow a host to sniff unicast traffic from all hosts connected to a switch?
The switch must be configured to mirror traffic to the sniffer's port.
What type of routing table entry is shown below? S* 0.0.0.0/0 [1/0] via 192.0.2.1
This is a static entry for the default route. The destination 0.0.0.0/0 represents an unknown network and will be matched if there is no match to a more specific destination. 192.0.2.1 is the gateway or next hop router for the default route.
Two client hosts have intermittent connectivity issues when accessing a server service on another subnet. No other client hosts exhibit this problem. What configuration problem might you suspect?
This is likely to be caused by a duplicate IP or MAC address. Replies from the server will be misdirected between the two hosts.
What is the significance of the address 127.0.0.1?
This is the default loopback address for most hosts. The loopback address facilitates testing the TCP/IP implementation on a host.
Which three means of establishing a theory of probable cause refer to the OSI model?
Top-to-bottom, bottom-to-top, and divide and conquer.
At which OSI layer is the concept of a port number introduced?
Transport.
True or False? A router will not forward a packet when the TTL field is 0.
True.
True or False? Receiving an echo reply message indicates that the link between two hosts is operational.
True.
True or false? A managed switch should have auto MDI/MDI-X enabled by default.
True.
True or false? All the nodes shown in the following figure are in the same collision domain. (image of 6 devices plugged into 1 hub)
True. Hubs work at the physical layer (layer 1) and just repeat the same signal out of each port.
You need to provision modular SFP+ transceivers to support a 10 gigabit link between two switches using an existing fiber cable. What two characteristics must you check when ordering the transceivers?
Use an appropriate Ethernet standard and wavelength for the type and grade of fiber and link distance (10GBASE-SR versus 10GBASE-LR, for instance) and match the connector type of the existing cable (LC or SC, for instance).
A Windows client workstation cannot access a help desk application server by its name support.515support.com. The service can be accessed using its IP address. What two command line tools should you use to identify possible causes of this issue?
Use ipconfig to report the DNS servers that the client is trying to use and verify they are correct. Use ping to verify connectivity with the DNS servers.
Convert the binary value 11110010 to decimal.
Work out the value of the binary place positions: 128*1 + 64*1 + 32*1 + 16*1 + 8*0 + 4*0 + 2*1 + 1*0. Sum the result to derive the answer 242.
Can you safely connect a server to a PoE+ enabled port or should you disable PoE first?
You can connect the server. PoE uses a detection mechanism to determine whether to supply power.
Which of the following IPv6 addresses is a valid unicast host address? fe80::218:8bff:fea7:bd37 fe80::219:d2ff::7850 ff02::219:d2ff:fea7:7850 ::/128
fe80::218:8bff:fea7:bd37
