Question 1

On a Cisco router, which type of banner configuration is typically used to display a general Message of the Day (MOTD) to all terminals that connect to the device?

Accepted Answer

Introduction / Context: This question covers basic administrative configuration on Cisco routers. Banners are used to display messages such as legal notices, security warnings, or informational text when users connect to the device. Different banner types exist for different moments in the login process, so you must know which one is associated with general messages shown to all terminals. Given Data / Assumptions: - We are configuring a Cisco router or similar IOS based device. - We want a message to appear when any terminal connects, regardless of whether it is console, Telnet, or SSH. - The message is a general Message of the Day, not necessarily limited to just before or after authentication. - The question asks which banner type is typically used for this MOTD behavior. Concept / Approach: Cisco IOS supports several banner types, including banner motd (Message of the Day), banner login, and banner exec. The MOTD banner is displayed before the login prompt on most lines and is intended for general informational or warning messages. The login banner appears right before the username or password prompts, and the exec banner displays messages when an EXEC session is started after authentication. When exam questions refer to showing a message to all terminals in a generic way, they almost always expect banner motd as the correct answer. Step-by-Step Solution: Step 1: Recall that banner motd is the command used to configure a Message of the Day banner on Cisco IOS.Step 2: Understand that this banner is displayed to most users when they connect to the device, regardless of whether it is via console or remote lines.Step 3: Recognize that banner login is more specifically associated with legal warnings displayed just before login prompts, although in many environments MOTD and login banners may both be used.Step 4: Note that banner exec is displayed when a user enters an EXEC shell after authentication, which is a different stage of the session.Step 5: Choose banner motd as the banner type that matches the description of a general message to all terminals. Verification / Alternative check: In practice, you can configure banner motd #Welcome to this router# on a lab device and then log in via console and Telnet. You will see the MOTD banner text displayed before the login prompts. If you also configure a login banner, it will appear closer to the username prompt. This confirms that the MOTD is the general, all-terminals message, which is what this question targets. Why Other Options Are Wrong: banner login is also common, but exam wording that emphasizes “Message of the Day” or a generic banner to all users is specifically about banner motd. banner exec is tied to EXEC session start, not initial connection. banner slip-ppp is related to older dial-up technologies and is not the general purpose banner most administrators use. banner incoming is not a standard Cisco IOS command for typical router configuration in this context, making it an incorrect distractor. Common Pitfalls: Students sometimes confuse banner motd and banner login, especially because both can display legal or informational messages. Another pitfall is to assume that any banner keyword will work the same way, when each is tied to a different stage of the login process. Remembering that the term “Message of the Day” maps directly to banner motd helps lock in the correct answer quickly. Final Answer: You use the banner motd command to configure a general Message of the Day banner that is displayed to all terminals connected to the router.

Question 2

When issuing a ping command on a Cisco device, which symbol in the ping output indicates that an echo request was successful?

Accepted Answer

Introduction / Context: This question evaluates your familiarity with Cisco ping output symbols, a simple but important skill for quick troubleshooting at the command line. Cisco IOS uses specific characters to indicate success or different types of failure when you ping a destination, and recognizing them helps you understand network behavior at a glance. Given Data / Assumptions: - You are running the ping command from a Cisco router or switch. - The output shows a series of characters, one for each ICMP echo request sent. - Different characters such as !, ., U, and others represent different results. - The question asks which symbol specifically indicates a successful ping reply. Concept / Approach: When you ping from a Cisco device, the IOS sends multiple ICMP echo requests. For each packet, it prints a single character: an exclamation mark (!) for a successful reply, a period (.) for a timeout (no reply), a U for destination unreachable, and other letters for different ICMP error codes. The exclamation mark is the one you want to see when checking basic connectivity, as a sequence of !!!!! typically indicates that the test was successful for all packets sent. Step-by-Step Solution: Step 1: Recall from IOS documentation or lab practice that ping output frequently displays lines such as !!!!! or ..!U. Each character corresponds to one probe.Step 2: Remember that the exclamation mark (!) means the ICMP echo reply was received within the timeout period.Step 3: Recognize that a period (.) indicates a timeout with no reply, which is not successful.Step 4: Note that U usually indicates an ICMP destination unreachable message, again not a success.Step 5: Choose ! as the correct symbol indicating a successful ping. Verification / Alternative check: In a lab, ping a reachable IP address from a Cisco router. You will see output like Sending 5, 100-byte ICMP Echos: !!!!!. This confirms that each ! represents a successful reply. If you ping an unreachable address, you will see sequences with . or U, indicating the failure to receive a proper echo reply. Why Other Options Are Wrong: The period (.) is explicitly documented as a timeout indicator, not a success. The question mark (?) is not used as a standard ping result symbol in Cisco IOS; it is more commonly related to help prompts in command line editing. U indicates destination unreachable, which is a failure. F is not a standard ping output code for success in IOS and is included only as a distractor. Common Pitfalls: Some learners focus only on whether ping shows 0% or 100% success and do not pay attention to the per-packet symbols, which can provide more detail. Another mistake is to confuse . as meaning “OK” and ! as some form of warning, because exclamation marks often signal alerts in other contexts. In Cisco ping output, however, ! is good news. Remembering this detail speeds up CLI troubleshooting. Final Answer: On a Cisco device, the ! symbol indicates that a ping echo request was successful.

Question 3

On a Cisco router, which global configuration command correctly changes the hostname of the device to a new name?

Accepted Answer

Introduction / Context: This question checks your understanding of basic Cisco IOS configuration modes and the correct syntax for changing a router's hostname. Although simple, this task is performed frequently and appears in many introductory configuration labs and exam questions. Given Data / Assumptions: - You are working on a Cisco router using the command line interface. - You want to change the hostname from its default (for example, Router) to a new, more descriptive name. - You must know both the correct configuration mode and the exact command syntax for changing the hostname. Concept / Approach: On Cisco IOS, the hostname is configured in global configuration mode, not from user EXEC, privileged EXEC, or routing protocol sub-configuration modes. The exact command is hostname followed by the desired name, such as hostname Branch-R1. When you press Enter, the router prompt changes immediately to reflect the new hostname, confirming the change. The command does not include additional keywords like router-name or host name; it is simply hostname. Step-by-Step Solution: Step 1: From the initial prompt, enter privileged EXEC mode using enable if necessary.Step 2: Enter global configuration mode with configure terminal.Step 3: At the router(config)# prompt, use the command hostname newname, replacing newname with your chosen router name.Step 4: Observe that the command prompt changes to newname(config)#, indicating that the hostname has been updated.Step 5: Save the configuration with copy run start or write memory if you want the change to persist after reload. Verification / Alternative check: You can verify the configured hostname in several ways. The most obvious is the appearance of the new name in the CLI prompt. You can also use show running-config and look for the hostname line near the top of the configuration. If the new name is present, then the change was applied correctly in global configuration mode. Why Other Options Are Wrong: Option A uses host name with a space and is entered in privileged EXEC mode, which is invalid syntax and the wrong mode. Option B shows router(config-router)#, which is a router protocol subconfiguration mode, not global configuration mode. Option C uses the user EXEC prompt router> and again uses host name with a space, which is incorrect. Option E invents a router-name keyword that is not supported by IOS; the proper keyword is hostname. Only option D shows the correct mode and the correct command syntax. Common Pitfalls: New learners sometimes confuse host name and hostname or issue the command from the wrong mode, leading to error messages or no effect. Another pitfall is forgetting to save the configuration, causing the hostname to revert on reboot. Remember that most device-wide settings such as hostname, domain name, and passwords are configured in global configuration mode using simple, specific commands. Final Answer: The correct command is router(config)#hostname newname, entered from global configuration mode.

Question 4

On a Cisco Catalyst 2960 switch, what does an amber SYST (system) LED typically indicate about the switch status?

Accepted Answer

Introduction / Context: This question tests your ability to interpret front-panel LEDs on a Cisco Catalyst 2960 switch. These visual indicators provide quick information about the device status without needing to log in, which is especially helpful during initial installation or when troubleshooting hardware issues in a wiring closet or data center. Given Data / Assumptions: - The device is a Cisco Catalyst 2960 switch. - We are looking specifically at the SYST (system) LED on the front panel. - The LED is amber in color, not off or green. - The question asks what this amber state typically means for the switch. Concept / Approach: According to Cisco documentation, the SYST LED indicates overall system status. On many Catalyst switches, a green SYST LED means the system is receiving power and operating normally. An off SYST LED usually means there is no power. An amber SYST LED generally indicates that the switch has detected a system problem, such as failing its power-on self-test (POST) or experiencing a major hardware or software fault. This status signals that the switch is not operating correctly and requires attention. Step-by-Step Solution: Step 1: Recall the common meanings of SYST LED colors: green for normal operation, off for no power, and amber for fault conditions.Step 2: Understand that POST is a series of diagnostics run when the switch boots; failing POST often causes the SYST LED to remain amber.Step 3: Recognize that a persistent amber SYST LED means the switch is not in a healthy, fully operational state.Step 4: Rule out interpretations that suggest normal operation or minor issues, because hardware failure or serious faults are more strongly indicated by amber.Step 5: Choose the option that describes the switch having encountered a problem, such as failing POST or another system fault. Verification / Alternative check: When deploying or troubleshooting a 2960, you can observe the SYST LED during boot. It may briefly show different states, but if it settles on green, the switch is generally fine. If it remains amber, documentation and field experience confirm that the switch has encountered a hardware or software issue, often requiring further diagnostics, a power cycle, or even replacement. This behavior aligns with the meaning expressed in the correct option. Why Other Options Are Wrong: Option A incorrectly states that amber means normal operation; in fact, green indicates normal status. Option B confuses system status with spanning-tree port LEDs; bridging loops are detected via STP but not indicated purely by the SYST LED in this way. Option C suggests that IOS loading is represented by amber, which is not the standard documented meaning for a steady amber SYST LED. Option E invents a low-power mode status that is not represented by the SYST LED on a 2960. Common Pitfalls: A common mistake is to assume that any light being on must be good, when in fact the color and whether it is blinking or steady matter greatly. Another pitfall is to misinterpret port LEDs as system LEDs or vice versa. Reading the hardware installation guide for your specific switch model and remembering that amber on the SYST LED usually signals a fault helps avoid misdiagnosis during troubleshooting. Final Answer: An amber SYST LED on a Catalyst 2960 switch typically indicates that the switch has encountered a system problem, such as failing its POST or another serious fault, and is not operating normally.

Question 5

As a network administrator, you want IP addresses to be assigned automatically to hosts on your network. Which protocol is typically used to make IP address assignment easy and centralized?

Accepted Answer

Introduction / Context: This question tests your understanding of basic network infrastructure protocols, specifically which one is responsible for automatically assigning IP configuration details to client devices. Automating IP address assignment makes network administration simpler and reduces configuration errors on large networks. Given Data / Assumptions: - There are multiple hosts (such as PCs, laptops, phones) that need IP addresses on a network. - The administrator wants an easy, centralized way to assign IP addresses and related settings rather than configuring each host manually. - Several well-known network protocols are listed as options, including DNS, DHCP, HSRP, and NTP. Concept / Approach: Dynamic Host Configuration Protocol is designed to automatically assign IP configuration parameters to client devices. These parameters typically include the IP address, subnet mask, default gateway, and one or more DNS server addresses. Clients send DHCPDISCOVER messages on the network to locate a DHCP server, which then offers configuration information. When hosts are configured to obtain an address automatically, DHCP significantly reduces manual work and misconfigurations. Step-by-Step Solution: Step 1: Recall that DHCP is the protocol specifically created to dynamically provide IP configuration to hosts.Step 2: Understand that DNS resolves hostnames to IP addresses, but does not assign addresses to clients.Step 3: Recognize that HSRP is a Cisco redundancy protocol used to provide highly available default gateways, not endpoint addressing.Step 4: Note that NTP synchronizes time between devices and has nothing to do with address assignment.Step 5: Choose DHCP as the protocol that makes assigning IP addresses to hosts easy and centralized. Verification / Alternative check: In practice, if clients are configured with “Obtain an IP address automatically,” they send DHCP requests on startup. If a DHCP server is reachable, they receive an IP configuration lease. You can verify this on a host by using ipconfig /all on Windows or ip addr show on Linux to see that the address came from DHCP. Disabling the DHCP server and observing that clients no longer receive addresses further confirms the dependency. Why Other Options Are Wrong: DNS is critical for name resolution, but it does not assign addresses to devices. HSRP only provides a virtual IP for gateway redundancy between routers; it does not allocate client IPs. NTP is about time synchronization, and TFTP is used for simple file transfers, such as copying IOS images, not for address assignment. Only DHCP is designed for automatic host IP configuration. Common Pitfalls: Some learners conflate DNS and DHCP because both are often provided by the same server (such as a Windows domain controller or a firewall appliance). Another pitfall is thinking HSRP assigns IP addresses because it is associated with a default gateway IP. Remember: DHCP hands out addresses and configuration to clients; DNS resolves names; HSRP keeps the default gateway highly available; NTP synchronizes clocks. Final Answer: Dynamic Host Configuration Protocol (DHCP) is the protocol used to automatically and centrally assign IP addresses and related configuration to hosts.

Question 6

In the shown RIP topology, you do not want router R3 to receive any RIP routing updates. Which configuration change on R1 is typically used to prevent sending RIP updates out a specific interface toward R3 while still allowing RIP elsewhere?

Accepted Answer

Introduction / Context: This question deals with controlling the behavior of distance-vector routing protocols, specifically RIP, on a per-interface basis. There are many situations where you want a router to participate in a routing protocol on some interfaces but not send updates out others, for example when connecting to an end host or a router that should not receive dynamic routes. Given Data / Assumptions: - RIP is the routing protocol in use across multiple routers (R1, R2, R3, etc.). - Router R3 is connected to R1, but you do not want R3 to receive RIP updates from R1. - You still want R1 to run RIP on its other interfaces and exchange routes with other routers in the topology. - The question asks which configuration change should be made to achieve this behavior. Concept / Approach: In Cisco IOS, the passive-interface command within a routing protocol configuration tells the router not to send routing updates out that interface, while still listening for updates on other interfaces and advertising the connected network in the routing process. With RIP, making an interface passive effectively stops RIP broadcast or multicast updates from going out that interface. This is a clean way to prevent a neighbor from receiving updates without disabling RIP globally or changing protocols. Step-by-Step Solution: Step 1: Enter router configuration mode for RIP on R1 using router rip.Step 2: Identify the interface facing R3, for example serial0/0 or fastethernet0/1, depending on the topology.Step 3: Use the command passive-interface <interface-name> to stop RIP updates from being sent out that interface.Step 4: Confirm that R1 still participates in RIP on other interfaces and learns routes from the rest of the network.Step 5: Verify that R3 no longer receives RIP updates from R1 by checking its routing table or debug output. Verification / Alternative check: In a lab, before configuring passive-interface, you can run debug ip rip on R3 and see periodic incoming updates from R1. After configuring passive-interface on the relevant interface on R1, those updates will stop, while other routers still exchange RIP updates. R3's routing table will no longer be populated with routes learned from R1 by RIP, which confirms that the configuration change had the intended effect. Why Other Options Are Wrong: Option B incorrectly suggests that no configuration is needed, but RIP will send updates out all interfaces that match the network statements by default. Option C complicates the design by adding subinterfaces and VLANs without directly addressing RIP behavior. Option D replaces RIP with OSPF across the entire network, which is far more disruptive and outside the scope of the requirement. Option E disables routing on R3 itself, which may break other functions and is not necessary just to stop R3 from receiving RIP updates from R1. Common Pitfalls: Some administrators attempt to remove the network statement for the R3-facing network from R1's RIP configuration, but this can prevent R1 from advertising that connected network to others. Another pitfall is using distribute-lists when simply suppressing updates on a given interface would be simpler. Remember that passive-interface is the standard, exam-tested tool for suppressing routing protocol advertisements on a per-interface basis while keeping the protocol active elsewhere. Final Answer: You should configure a passive-interface on R1 for the interface that connects to R3 so that R1 does not send RIP updates out toward R3.

Question 7

Within the OSI model, with which layer are LAN switches primarily associated when forwarding Ethernet frames based on MAC addresses?

Accepted Answer

Introduction / Context: This question focuses on mapping common network devices to layers of the OSI reference model. LAN switches are ubiquitous in modern Ethernet networks, and understanding which OSI layer they primarily operate at helps clarify their functions and limitations in forwarding traffic. Given Data / Assumptions: - We are referring to traditional layer 2 LAN switches, not multilayer or layer 3 switches. - The switch forwards Ethernet frames based on destination MAC addresses. - We want to know which OSI layer is most closely associated with this behavior. Concept / Approach: The OSI model defines the Data Link layer as responsible for framing, MAC addressing, and access control on the local network segment. LAN switches examine the MAC address fields in Ethernet frames, maintain a MAC address table, and forward frames out the appropriate ports based on that table. These functions clearly align with the Data Link layer. While switches also depend on Physical layer functions to send bits over the medium, their core intelligence in terms of forwarding decisions resides at layer 2. Step-by-Step Solution: Step 1: Recall that MAC addresses and Ethernet framing are defined at the Data Link layer (layer 2) of the OSI model.Step 2: Recognize that a LAN switch examines the destination MAC address in the frame header to decide which port to forward the frame out of.Step 3: Understand that switches build a MAC address table by learning source MAC addresses on incoming frames.Step 4: Note that the Network layer (layer 3) deals primarily with IP addresses and routing, which is the job of routers or layer 3 switches.Step 5: Conclude that the Data Link layer is the correct OSI layer associated with LAN switching based on MAC addresses. Verification / Alternative check: Textbooks and certification study guides routinely describe legacy hubs as layer 1 devices, switches as layer 2 devices, and routers as layer 3 devices within the OSI context. When you inspect switch documentation, you see references to MAC address tables and VLAN tagging, both of which are Data Link layer concepts. This consistent classification confirms that LAN switches belong to the Data Link layer in most exam questions. Why Other Options Are Wrong: The Transport layer (layer 4) is concerned with end-to-end transport such as TCP and UDP, not MAC-based forwarding. The Physical layer (layer 1) concerns voltages, cables, and bit transmission, which is below switching logic. The Network layer (layer 3) focuses on IP addressing and routing decisions, which routers handle. The Session layer manages sessions between applications and is not directly involved in MAC-based forwarding. Only the Data Link layer accurately reflects the switch's main role in processing Ethernet frames. Common Pitfalls: Some learners confuse multilayer switches, which can operate at layer 3, with basic LAN switches. Exam questions that simply mention “LAN switches” without explicit layer 3 context almost always refer to layer 2 devices. Another pitfall is thinking that because switches physically connect devices, they belong to the Physical layer, ignoring the logic they apply based on MAC addresses. Remember that intelligence based on MAC addresses is a hallmark of the Data Link layer. Final Answer: LAN switches that forward frames based on MAC addresses are primarily associated with the Data Link layer of the OSI model.

Question 8

Within the OSI model, with which layer are WAN encapsulation protocols such as HDLC, Frame Relay and PPP primarily associated?

Accepted Answer

Introduction / Context: This question tests your knowledge of how various WAN technologies relate to the OSI model. Protocols such as High-Level Data Link Control, Frame Relay, and Point-to-Point Protocol are classic examples of wide area network encapsulations, and correctly placing them in the OSI stack is important for understanding their function and how they interact with IP routing. Given Data / Assumptions: - We are considering protocols used over WAN links, such as HDLC, Frame Relay, and PPP. - These protocols handle framing, addressing, and sometimes basic reliability on serial or virtual circuits. - The question asks which OSI layer they belong to primarily. Concept / Approach: The Data Link layer of the OSI model is responsible for framing, physical addressing at the link level, and controlling access to the physical medium. HDLC, Frame Relay, and PPP define how data is framed and transmitted over point-to-point or switched WAN links. They specify encapsulation, addressing fields, and sometimes error detection. All of these functions clearly correspond to Data Link layer responsibilities. The Physical layer underneath them handles the actual electrical, optical, or radio transmission of bits. Step-by-Step Solution: Step 1: Recall that Data Link layer protocols provide framing and link-level addressing for data traveling over a specific physical medium.Step 2: Recognize that HDLC defines frame structure, flags, control fields, and sometimes basic error handling for synchronous links.Step 3: Understand that Frame Relay provides virtual circuit identifiers (DLCIs) within its frames, again a Data Link layer function.Step 4: PPP defines encapsulation for IP and other protocols over point-to-point links, plus negotiation mechanisms like LCP, all of which sit at layer 2.Step 5: Conclude that these protocols are associated with the Data Link layer. Verification / Alternative check: Network diagrams and certification materials frequently describe Ethernet, HDLC, Frame Relay, and PPP as examples of layer 2 technologies. When configuring serial interfaces on Cisco routers, you select encapsulation hdlc or encapsulation ppp as layer 2 settings under the interface, while IP addresses are configured separately at layer 3. This separation of concerns confirms their role at the Data Link layer. Why Other Options Are Wrong: The Physical layer covers only the transmission medium and signaling, not the framing and addressing provided by HDLC, Frame Relay, or PPP. The Transport layer deals with TCP and UDP, which run on top of IP, not directly on WAN encapsulations. The Network layer handles IP routing and addressing, which are carried inside these encapsulation frames. The Application layer is far removed from link-level protocols and is not responsible for framing on WAN links. Common Pitfalls: Some learners mistakenly associate WAN protocols automatically with the Physical layer because they imagine serial cables and links. Others confuse HDLC, PPP, and Frame Relay with layer 3 because they are configured on router interfaces that also have IP settings. Remember that IP is a separate layer 3 configuration, while these WAN encapsulation protocols define how layer 3 packets are carried over layer 2 links. Final Answer: HDLC, Frame Relay and PPP are Data Link layer protocols in the OSI model.

Question 9

In networking terminology, what is meant by same-layer interaction in a layered reference model such as the OSI model?

Accepted Answer

Introduction / Context: This question focuses on the conceptual idea of how layered networking models such as the OSI or TCP/IP models describe communication. The term same-layer interaction refers to how protocols at the same layer on different devices interact logically, even though the data is physically transported through all layers along the path. Given Data / Assumptions: - We are using a layered networking model such as OSI for conceptual understanding. - Different layers provide different services (for example, HTTP at Application, TCP at Transport, IP at Network). - The question asks specifically about the meaning of same-layer interaction between computers. Concept / Approach: In layered models, communication is often described in two ways: adjacent-layer interaction and same-layer interaction. Adjacent-layer interaction involves services and interfaces between one layer and the layer directly above or below on the same device. Same-layer interaction refers to the logical communication between protocols operating at the same layer on different devices. For example, TCP on one host is logically communicating with TCP on another host, even though the actual bits pass through many layers, cables, and intermediate devices. Step-by-Step Solution: Step 1: Recall that each layer on a device uses the services of the layer below and provides services to the layer above; these are adjacent-layer interactions.Step 2: Understand that same-layer interaction occurs between peer protocols on different devices, such as TCP to TCP or HTTP to HTTP.Step 3: Recognize that protocols at the same layer agree on rules and formats (headers, sequence numbers, acknowledgements) to enable reliable communication.Step 4: Note that this interaction is logical; the data still passes through the entire protocol stack and across the network infrastructure.Step 5: Choose the option that describes two computers using a protocol defined at the same layer of a networking model to communicate with each other. Verification / Alternative check: Consider TCP at the Transport layer: while data is being sent from one application to another, each host's TCP implementation handles segmentation, reliability, and flow control. Documentation often states that TCP on one host logically communicates with TCP on the other host, which is exactly same-layer interaction. Similarly, IP on one router logically interacts with IP on another router at the Network layer, even though the actual transmission uses lower layers and physical media. Why Other Options Are Wrong: Option A confuses the OSI model with the Cisco three-layer campus design model, which is a different conceptual tool. Option B describes an interaction confined entirely within a single layer on one device, which is more about internal processing than same-layer communication between devices. Option C describes adjacent-layer interaction inside one device, not same-layer interaction between peers. Option E brings in collision domains and medium access, which are Data Link layer concerns but not the definition of same-layer interaction. Common Pitfalls: Students sometimes mix up the terms adjacent-layer and same-layer interaction, especially when both are discussed in the same chapter. Another pitfall is to think that same-layer interaction means the data never touches other layers, when in reality the model is describing logical, not physical, behavior. Remember that same-layer interaction is about protocols at the same layer on different devices using common rules to communicate. Final Answer: Same-layer interaction means that two computers use a protocol defined at the same layer of a networking model to communicate with each other across the network.

Question 10

On an Ethernet network using CSMA/CD, when a device has a frame ready to send, what is the first action taken by the CSMA/CD logic before transmitting?

Accepted Answer

Introduction / Context: This question tests your understanding of the Carrier Sense Multiple Access with Collision Detection method used in traditional shared Ethernet networks. Although many modern networks are switched and full duplex, CSMA/CD remains an important concept for exams and for understanding how Ethernet evolved. Given Data / Assumptions: - The Ethernet network is operating in half-duplex mode and uses CSMA/CD. - A device on the network has a frame ready to transmit. - The question asks what the CSMA/CD logic does first before sending the frame. Concept / Approach: CSMA/CD stands for Carrier Sense Multiple Access with Collision Detection. Carrier sense means that each device listens to the medium to see whether a signal (a carrier) is already present. Multiple access means many devices share the same medium. Collision detection means that if two devices transmit at the same time and a collision occurs, they detect it and back off before retrying. The first step in this process is to listen to the medium to determine whether it is currently idle. Only when the medium is idle is the device allowed to transmit. Step-by-Step Solution: Step 1: Recall that carrier sense requires a device to listen for existing traffic on the cable before transmitting.Step 2: When the device has a frame to send, it first checks whether the medium is busy or idle.Step 3: If the medium is busy, the device waits until it becomes idle before attempting transmission.Step 4: Once the medium is idle, the device transmits and continues to monitor the medium to detect any collision.Step 5: If a collision is detected, a jamming signal is sent and the device performs a backoff algorithm before retrying. Verification / Alternative check: Ethernet standards and textbooks describe CSMA/CD in this sequence: listen (carrier sense), transmit if idle, detect collisions, send jamming, and back off. This is quite different from token-based approaches such as Token Ring, where a token is passed between devices. Observing how hubs and early shared Ethernet behaved in simulations or labs aligns with this order of operations. Why Other Options Are Wrong: Option A describes token passing, which is used in Token Ring and other technologies, not in Ethernet CSMA/CD. Option B mentions a jamming signal, but this is sent only after a collision is detected, not before transmission. Option C refers to discovering whether the destination is on the same subnet, which is not the first step in CSMA/CD media access control. Option E suggests immediate transmission without checking the medium, which would lead to constant collisions and is the opposite of carrier sense. Common Pitfalls: Some learners confuse CSMA/CD with token-based access methods and expect a token to be present. Others focus on collision detection and jamming but forget that listening to the medium is the first step. Also, many students learn CSMA/CD historically without realizing that full-duplex switched Ethernet no longer uses collision detection, which can lead to confusion when comparing old and new environments. Remember the name itself: Carrier Sense comes first. Final Answer: When a device is ready to send a frame on a CSMA/CD Ethernet, it first listens to the Ethernet to see if the medium is busy or idle before attempting to transmit.

Question 11

In Ethernet networks, what does the acronym CSMA/CD stand for?

Accepted Answer

Introduction / Context: This question checks your recall of a fundamental Ethernet concept: the meaning of CSMA/CD. Even though modern switched full-duplex Ethernet no longer relies on collision detection, the acronym and its behavior are core exam topics and important historically for understanding shared-media networks. Given Data / Assumptions: - We are working with traditional Ethernet that used CSMA/CD on shared media segments. - CSMA/CD is an access method describing how devices share the medium and detect collisions. - The question asks for the full phrase represented by the acronym. Concept / Approach: CSMA/CD stands for Carrier Sense Multiple Access with Collision Detection. Each part of the phrase describes an aspect of the access method. Carrier Sense means devices listen for existing traffic before sending. Multiple Access refers to the fact that many devices share the same collision domain. Collision Detection means devices monitor the medium while transmitting and detect if a collision occurs, at which point they send a jamming signal and back off before retrying. Step-by-Step Solution: Step 1: Recall that CSMA/CD is a well known Ethernet access method, and the letters C, S, M, A, C, and D each correspond to words.Step 2: Match C to Carrier, S to Sense, M and A to Multiple Access, and C and D to Collision Detection.Step 3: Combine these into the standard phrase Carrier Sense Multiple Access with Collision Detection.Step 4: Verify that this phrase accurately describes listening to the medium, sharing access, and detecting collisions.Step 5: Choose the answer option that exactly matches this standard phrase. Verification / Alternative check: Any networking textbook, standard, or Cisco exam guide that introduces legacy Ethernet will spell out CSMA/CD as Carrier Sense Multiple Access with Collision Detection. The phrase aligns with the operational description you see in diagrams showing devices listening, transmitting, detecting collisions, and backing off. This consistent usage across sources confirms that this is the correct expansion of the acronym. Why Other Options Are Wrong: Options A and C replace Access with Action and use incorrect terms like Detonation, which are not used in networking. Option B uses Collisionless Delivery, which contradicts the very idea of collision detection and is not accurate for shared Ethernet. Option E invents Centralized Switching Multiple Access, which does not correspond to any standard Ethernet terminology. Only option D matches the documented and widely accepted meaning of CSMA/CD. Common Pitfalls: Some learners misremember the M and A as something other than Multiple Access, or think the C and D stand for Collision Domain rather than Collision Detection. Others confuse CSMA/CD with CSMA/CA, which is Collision Avoidance, used in wireless LANs. Keeping the wires-versus-air distinction in mind helps: wired Ethernet historically used collision detection, while Wi-Fi relies on collision avoidance. Final Answer: CSMA/CD stands for Carrier Sense Multiple Access with Collision Detection.

Question 12

In IP Quality of Service (QoS) for real time voice and video traffic, what does the term jitter refer to?

Accepted Answer

Introduction / Context: Jitter is a very important Quality of Service concept for real time applications such as Voice over IP, video conferencing, and interactive gaming. These applications do not just care about how fast a single packet arrives, but about how consistent the delay is from packet to packet. The question asks you to identify the correct definition of jitter in the context of IP networking and QoS. Given Data / Assumptions: We are dealing with IP packets that carry voice or video streams across a network. Packets may experience different delays as they pass through routers, switches, and queues. We want to understand what network engineers mean when they talk about jitter. The context is QoS for real time traffic, not general file transfer or bulk data. Concept / Approach: Jitter is defined as the variation in packet delay, also called delay variation. If one packet in a voice stream arrives in 40 milliseconds and the next arrives in 100 milliseconds, the delay has not been consistent. Even if the average delay is acceptable, this variation can cause choppy audio or video. To manage jitter, devices such as IP phones often use a jitter buffer, which collects packets and plays them out at a steady rate to mask the variable arrival times. Step-by-Step Solution: 1. Focus on the QoS context in the question. It mentions colleagues discussing jitter while working with QoS for IP networks. 2. Recall that delay is the time taken for a packet to travel from source to destination, while jitter is not simply the delay itself. 3. Understand that jitter measures how much the delay varies from packet to packet within a flow. 4. Compare this understanding with each option. Look for the answer that explicitly mentions variation in delay between packets. 5. Option a states that jitter is the variation in one way delay experienced by packets, which exactly matches the QoS definition of jitter. Verification / Alternative check: A quick way to verify is to think about the problems that jitter causes. Voice calls where some packets arrive late and out of order sound broken, even if very few packets are lost. This matches the idea of variable delay rather than total bandwidth or total packet loss. Network monitoring tools often graph jitter as a measure of delay variation in milliseconds for a given flow. Why Other Options Are Wrong: Option b is wrong because total bandwidth is throughput capacity, not jitter. Option c is wrong because it describes packet loss rate, not delay variation. Option d is incorrect because the difference between upload and download speed is related to service type, not to jitter in a specific traffic flow. Common Pitfalls: A common mistake is to confuse jitter with latency or packet loss. Latency is the fixed or average delay, while jitter is how much that delay changes from packet to packet. Another misconception is to treat jitter as a human perception term only for audio, but in reality it is a measurable network metric that affects many applications. Final Answer: Jitter is the variation in the one way delay experienced by packets as they travel across the network.

Question 13

If two laptops are exchanging data directly with each other using an IEEE 802.11g wireless connection, in which operating mode are they working?

Accepted Answer

Introduction / Context: Wireless local area networks that use standards such as IEEE 802.11b, 802.11g, or 802.11n can operate in different modes. Two of the most important modes are infrastructure mode and ad hoc mode. The question describes two laptops that are communicating directly with each other over 802.11g, with no mention of a wireless router or access point. You are asked to identify the correct mode for this situation. Given Data / Assumptions: Two laptops have wireless network interfaces that support IEEE 802.11g. The laptops are exchanging data directly with each other. No access point, wireless router, or other infrastructure device is mentioned. The context is basic wireless networking terminology for exam preparation. Concept / Approach: In infrastructure mode, all wireless devices communicate through a central access point, which connects them to the rest of the network. In ad hoc mode, devices connect directly to each other, forming a peer to peer network called an Independent Basic Service Set. The key phrase in the question is that the laptops are exchanging data directly with each other, which strongly suggests ad hoc operation rather than infrastructure based communication. Step-by-Step Solution: 1. Identify the entities in the scenario: there are only two laptops and no other wireless device is mentioned. 2. Recall that infrastructure mode requires a wireless access point that coordinates communication between clients. 3. Note the word directly in the question, which implies that the laptops send frames to each other without a central access point. 4. Match this description to the wireless networking modes. Ad hoc mode is defined as peer to peer communication between stations without infrastructure. 5. Select the option that uses the correct term and also describes the peer to peer behavior. Verification / Alternative check: To verify, remember that in ad hoc mode each station talks directly to other stations, and the coverage area is limited to the range of the participating devices. In contrast, infrastructure mode extends coverage through access points and may connect to wired networks. If we imagine this scenario in a home or office, two laptops using an 802.11g link without a wireless router would need to be configured for ad hoc or computer to computer mode in their wireless settings. Why Other Options Are Wrong: Option b is incorrect because infrastructure mode always involves an access point or wireless router, which is not present. Option c, extended service set mode, is a variation of infrastructure mode with multiple access points and roaming, also not described here. Option d, bridge mode, refers to a device that connects two network segments and does not describe two laptops communicating directly as peers. Common Pitfalls: Students often confuse ad hoc mode with basic service set and extended service set terminology. Basic service set still typically refers to infrastructure mode with one access point. Another common mistake is to assume that any wireless communication automatically uses infrastructure mode, which is not true when devices are configured to connect directly without an access point. Final Answer: The laptops are operating in ad hoc mode, where they form a peer to peer wireless network without an access point.

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