Question 1

Network security practice: What are the two main types of access control lists (ACLs) used on routers and firewalls?

Accepted Answer

Introduction / Context:Access control lists (ACLs) are rule sets that permit or deny traffic based on criteria such as source, destination, and protocol. On many network platforms, especially Cisco IOS, two broad categories are emphasized for IP traffic filtering. Given Data / Assumptions: The numbered items are: 1 Standard, 2 IEEE, 3 Extended, 4 Specialized. We are referring to commonly taught ACL categories for IP filtering. Standard and extended ACLs are the canonical types in core certification curricula. Concept / Approach:Standard ACLs filter based on source IP only, typically applied as inbound or outbound on interfaces. Extended ACLs provide granular matching, including source, destination, protocol (TCP, UDP, ICMP), and ports. Other labels such as IEEE or specialized are not the established base types for IP ACLs in Cisco nomenclature. Step-by-Step Solution: Identify the two canonical categories: Standard and Extended.Map them to the options list: 1 corresponds to Standard and 3 to Extended.Select the pair 1 and 3. Verification / Alternative check:Configuration guides show ip access-list standard and ip access-list extended modes, confirming the two major types. Why Other Options Are Wrong: Pairs involving IEEE or Specialized do not reflect the standard Cisco categories. Standard and Extended are the widely recognized main types for IP ACLs. Common Pitfalls:Placing standard ACLs too close to the destination rather than the source; forgetting that extended ACLs should be placed close to the source for efficiency and specificity. Final Answer:1 and 3

Question 2

Point to Point Protocol (PPP): Which PPP component is responsible for dynamic addressing, authentication negotiation, and multilink configuration during link setup?

Accepted Answer

Introduction / Context:PPP is a data link layer protocol used over serial links. It is modular, using subprotocols for link establishment, authentication, and network layer parameter negotiation. Knowing which component handles which function is essential for troubleshooting. Given Data / Assumptions: LCP (Link Control Protocol) sets up, configures, and tests the data link connection. LCP negotiates options such as authentication (PAP or CHAP) and multilink parameters. NCP (Network Control Protocol) negotiates network layer options per protocol family, for example IPCP for IPv4 addressing. Concept / Approach:LCP is in charge of link establishment and option negotiation including authentication methods and multilink PPP. Dynamic IP address assignment is typically negotiated by an NCP like IPCP. However, many exam conventions summarize the overall PPP negotiation responsibilities under the umbrella of LCP during setup, emphasizing LCP as the controller for link options and capabilities. Step-by-Step Solution: Identify authentication and multilink negotiation as LCP functions.Recognize that dynamic addressing is negotiated by IPCP (an NCP) once the link is up.In aggregate exam framing, select LCP as the PPP component governing these setup capabilities. Verification / Alternative check:PPP negotiation traces show LCP Configure-Request/ACK exchanges for link options and IPCP exchanges for IP parameters, confirming the division of responsibilities. Why Other Options Are Wrong: NCP handles network layer specifics but not link authentication negotiation. HDLC is a framing method, not PPP control. X.25 is a packet switched network protocol suite unrelated to PPP control phases. Common Pitfalls:Confusing LCP and NCP roles; assuming HDLC and PPP control are interchangeable; forgetting that IPCP specifically negotiates IP addresses after LCP completes. Final Answer:LCP

Question 3

Cisco IOS configuration basics: Which command context is used to set the Telnet or SSH line password on a router for remote virtual terminal access?

Accepted Answer

Introduction / Context:Remote management of Cisco routers and switches typically uses virtual terminal lines (VTYs) for Telnet or SSH sessions. Correctly entering line configuration mode is required to set passwords and access control. Given Data / Assumptions: We want to configure login and password for remote sessions. Virtual terminal lines are addressed as vty 0 4 by default on many devices. Console and auxiliary lines are distinct from VTY lines. Concept / Approach:To set the password for remote access, enter global configuration mode and then the line configuration for vty 0 4. Inside that context, commands such as password, login, and transport input ssh or telnet are applied. Console and aux contexts do not control VTY authentication. Step-by-Step Solution: Enter configuration mode: configure terminal.Enter VTY line context: line vty 0 4.Set password and enable login; optionally configure transport and access-class. Verification / Alternative check:show running-config confirms the presence of a line vty 0 4 section with the configured password or AAA method lists. Why Other Options Are Wrong: line telnet 0 4 is not a valid IOS context. line aux 0 4 configures the auxiliary port, not remote VTY access. line con 0 configures the console line only. Common Pitfalls:Forgetting to enable login under the VTY lines; not using transport input ssh to disable insecure Telnet on production devices; relying on line passwords instead of AAA with local or remote user databases. Final Answer:line vty 0 4

Question 4

Point to Point Protocol (PPP): Which PPP component is used to identify and negotiate the Network layer protocol parameters on the link?

Accepted Answer

Introduction / Context:PPP separates link control from network layer parameter negotiation using distinct control protocols. After the link is established by LCP, the appropriate Network Control Protocol (NCP) runs to configure per protocol options such as IP addressing. Given Data / Assumptions: LCP handles link establishment, authentication negotiation, and option exchange. NCP family members include IPCP for IPv4 and IPV6CP for IPv6. The question asks specifically about identifying and negotiating Network layer protocols. Concept / Approach:NCP determines which Network layer protocols will be carried over the PPP link and negotiates their parameters. For example, IPCP can request IP address assignment dynamically, DNS options, and compression settings. Only after successful NCP negotiation is the network layer ready to pass traffic. Step-by-Step Solution: Recognize that LCP comes first to bring the link up.Identify NCP as the phase for per protocol configuration such as IPCP or IPV6CP.Choose NCP as the correct answer. Verification / Alternative check:PPP debug traces show LCP Configure messages followed by IPCP or IPV6CP Configure messages, confirming the division of labor. Why Other Options Are Wrong: ISDN is a physical access technology, not a PPP control protocol. HDLC provides framing but not parameter negotiation at the network layer. LCP handles link control, not network layer option negotiation. Common Pitfalls:Mixing up LCP and NCP roles; assuming address assignment happens during LCP; overlooking that multiple NCPs can run concurrently if multiple network protocols are used. Final Answer:NCP

Question 5

Internet Protocol version 6 (IPv6): What is the length of an IPv6 address as defined by the standard?

Accepted Answer

Introduction / Context:IPv6 was designed to overcome IPv4 address exhaustion and add features such as simplified header processing and built in multicast and anycast. A fundamental fact is the length of the IPv6 address space. Given Data / Assumptions: An IPv4 address is 32 bits long. IPv6 expands the address size to accommodate global growth and hierarchical allocation. Address length is expressed in bits, not bytes, in protocol specifications. Concept / Approach:IPv6 addresses are 128 bits long. They are commonly represented as eight groups of four hexadecimal digits separated by colons, with rules for zero compression and omission to shorten display while preserving the 128 bit value. Step-by-Step Solution: Recall the fundamental change from 32 bit IPv4 to 128 bit IPv6.Map 128 bits to the available options.Select 128 bits as the correct length. Verification / Alternative check:Any IPv6 packet capture or RFC reference shows addresses and prefix lengths computed over 128 bits (for example, /64 subnets). Why Other Options Are Wrong: 32 bits is IPv4, not IPv6. 128 bytes is incorrect by a factor of eight; addresses are 128 bits. 64 bits refers to common subnet size inside IPv6, not the full address length. 256 bits is not standard for IPv6. Common Pitfalls:Confusing the typical /64 subnet size with total address length; misinterpreting hexadecimal notation as implying bytes rather than bits. Final Answer:128 bits

Question 6

Network utilities: Which protocol is used by the Ping tool to test reachability and measure round trip time between hosts?

Accepted Answer

Introduction / Context:Ping is a ubiquitous diagnostic utility used to verify basic IP connectivity and delay. It works by sending special control messages and waiting for replies that indicate a target is reachable at the network layer. Given Data / Assumptions: Ping is not a transport layer application; it tests at the network and control level. The tool sends Echo Request messages and expects Echo Reply messages. Results include packet loss and round trip time statistics. Concept / Approach:Ping uses ICMP, the Internet Control Message Protocol. ICMP Echo Request and Echo Reply message types are used for the probing. ICMP is encapsulated in IP and is distinct from TCP and UDP. ARP and BootP serve other purposes on local networks and bootstrapping. Step-by-Step Solution: Identify the function of Ping: control plane reachability test.Associate Echo Request/Reply with ICMP message types.Select ICMP as the correct protocol used by Ping. Verification / Alternative check:Packet captures show ICMP type 8 (Echo Request) and type 0 (Echo Reply) exchanged during Ping operations. Why Other Options Are Wrong: TCP is a transport protocol used by applications like HTTP, not Ping control messages. ARP resolves MAC addresses on local segments but does not measure round trip time across IP networks. BootP is for bootstrapping and IP assignment on legacy systems. DNS resolves names to IP addresses but is not used for reachability probing. Common Pitfalls:Blocking ICMP at firewalls can cause Ping to fail even when hosts are reachable via TCP; assuming Ping tests every aspect of connectivity when it only exercises ICMP and routing. Final Answer:ICMP

Question 7

OSI reference model and hubs Within the OSI (Open Systems Interconnection) model, at which specific layer is a network hub defined or specified?

Accepted Answer

Introduction / Context:The OSI (Open Systems Interconnection) model is a seven-layer conceptual framework used to understand and standardize network communication. Each layer serves a unique function. The placement of devices like hubs, switches, and routers within this model is important for network engineers to correctly classify their roles and limitations. Given Data / Assumptions: We are identifying the OSI layer where a hub operates. Hubs are simple devices used to connect multiple computers in a network. They replicate and broadcast signals to all ports without filtering. Concept / Approach: A hub is considered a Physical layer (Layer 1) device. It deals strictly with bits and electrical signals, not frames or packets. Unlike switches or routers, a hub has no knowledge of MAC addresses or IP addresses. It merely repeats incoming signals to all other ports. Step-by-Step Solution: Identify that hubs do not inspect MAC addresses.Recall that switches operate at the Data Link layer, while routers work at the Network layer.Conclude that hubs fit in Layer 1 (Physical layer). Verification / Alternative check: Any networking fundamentals textbook or Cisco certification guide classifies hubs as Physical layer devices. They are sometimes called “multiport repeaters.” Why Other Options Are Wrong: Session layer: manages communication sessions, not hardware. Data Link layer: associated with switches and MAC addresses, not hubs. Application layer: deals with software applications, not physical devices. Transport layer: ensures end-to-end reliability, unrelated to hubs. Common Pitfalls: Confusing hubs with switches (which operate at Layer 2). Believing hubs filter traffic; they do not, they broadcast all frames. Final Answer: Physical layer

Question 8

Bridge Protocol Data Units (BPDUs) How frequently are BPDUs (Bridge Protocol Data Units) sent out by a Layer 2 device in a Spanning Tree Protocol (STP) enabled network?

Accepted Answer

Introduction / Context:BPDUs (Bridge Protocol Data Units) are messages exchanged by switches in a network running the Spanning Tree Protocol (STP). They are crucial in preventing loops and maintaining a loop-free topology. Their transmission frequency is standardized to ensure stable convergence. Given Data / Assumptions: We are considering IEEE 802.1D STP standard. Default configuration is assumed. BPDU timers are unchanged (Hello Time = 2 seconds). Concept / Approach: In IEEE 802.1D, switches send BPDUs by default every 2 seconds. These Hello BPDUs allow switches to share spanning tree information and elect the root bridge. Step-by-Step Solution: Recall the default Hello Time is 2 seconds.Verify that changes to Hello Time can alter this interval, but by default it is 2 seconds.Therefore, the correct answer is Every 2 seconds. Verification / Alternative check: Cisco networking documentation and IEEE 802.1D confirm the Hello BPDU interval of 2 seconds as the default setting. Why Other Options Are Wrong: Never: incorrect; BPDUs are the foundation of STP. 10 minutes or 30 seconds: too infrequent; would cause instability. 60 seconds: not a standard default timer. Common Pitfalls: Confusing BPDU interval with Max Age timer (20 seconds). Assuming BPDUs are sent only by the root bridge; all switches generate them. Final Answer: Every 2 seconds

Question 9

IP address classes Which class of IP address provides the largest number of host addresses by default (before subnetting is applied)?

Accepted Answer

Introduction / Context:Classful addressing divides IP addresses into Classes A, B, C, D, and E. Understanding the default number of host addresses available in each class is a fundamental networking concept for historical IP addressing schemes and subnetting. Given Data / Assumptions: We are considering traditional classful addressing, not CIDR (Classless Inter-Domain Routing). Host availability is determined before subnetting. Class D is reserved for multicast, Class E for experimental use. Concept / Approach: Class A networks use an 8-bit network prefix and a 24-bit host portion, providing 2^24 – 2 usable host addresses (about 16.7 million). Class B provides 65,534 hosts, Class C provides 254 hosts. Therefore, Class A has the most hosts by default. Step-by-Step Solution: Class A: 2^24 – 2 = 16,777,214 hosts.Class B: 2^16 – 2 = 65,534 hosts.Class C: 2^8 – 2 = 254 hosts.Thus, Class A has the largest number of default hosts. Verification / Alternative check: Textbook IP addressing tables confirm these values. Why Other Options Are Wrong: Class B and C: significantly fewer hosts. A and B combined: classes are not combined in addressing. Class D: reserved for multicast, not hosts. Common Pitfalls: Forgetting to subtract 2 for network and broadcast addresses. Confusing CIDR notation with classful addressing. Final Answer: Class A

Question 10

Virtual Local Area Networks (VLANs) Which of the following statements accurately describes VLANs in Cisco switching environments?

Accepted Answer

Introduction / Context:Virtual Local Area Networks (VLANs) allow segmentation of broadcast domains within a switch network. They improve performance, enhance security, and provide logical separation of traffic. Cisco supports VLANs extensively and also provides the VLAN Trunking Protocol (VTP) for management. Given Data / Assumptions: We are discussing VLANs in Cisco environments. VTP simplifies VLAN management across switches. Default VLAN configurations can vary by device. Concept / Approach: VTP (VLAN Trunking Protocol) allows VLAN configuration changes made on one switch to propagate to other switches in the same domain. This centralizes management but also requires careful version and mode settings to avoid network-wide disruptions. Step-by-Step Solution: Understand VLANs create separate broadcast domains.Recall that Cisco switches come with VLAN 1 by default, not two VLANs.Identify that VTP distributes VLAN configuration across a domain.Conclude that option D is the accurate statement. Verification / Alternative check: Cisco documentation confirms VLAN 1 exists by default, and VTP propagates VLAN information across switches in the same domain. Why Other Options Are Wrong: Two VLANs by default: incorrect, typically only VLAN 1 exists. VLANs require only Cisco devices: false; VLANs are industry-standard (IEEE 802.1Q). Limiting VTP domains to 10 switches: no such restriction. VLANs cannot be implemented: false; they are a core managed switch feature. Common Pitfalls: Assuming VLANs are Cisco-only; they are standardized (802.1Q). Misunderstanding default VLAN presence. Final Answer: VTP (VLAN Trunking Protocol) is used to send VLAN information to switches in a configured VTP domain

Question 11

Collision domains and switches When a network is segmented with a 12-port Ethernet switch, how many collision domains are created?

Accepted Answer

Introduction / Context:A collision domain is a network segment where data packets can collide with each other during transmission. The use of hubs, switches, and routers affects how many collision domains exist in a network. Switches are designed to reduce collision domains. Given Data / Assumptions: The device in question is a 12-port Ethernet switch. Each port on a switch operates independently. We are discussing traditional Ethernet with CSMA/CD in mind. Concept / Approach: Unlike hubs, which forward frames to all ports and thus create a single collision domain, switches create a separate collision domain for each port. Therefore, a 12-port switch creates 12 collision domains. Step-by-Step Solution: Identify number of switch ports: 12.Understand each port is isolated at Layer 2.Conclude total collision domains = number of ports = 12. Verification / Alternative check: Standard networking references confirm that switches eliminate collisions by dedicating a collision domain to each port. Why Other Options Are Wrong: 1: true only for hubs, not switches. 2 or 5: arbitrary incorrect numbers. 24: double the actual number of ports. Common Pitfalls: Confusing collision domains with broadcast domains. A switch still maintains a single broadcast domain unless VLANs are used. Final Answer: 12

Question 12

Purpose of the OSI model What is the primary reason the OSI (Open Systems Interconnection) model was developed?

Accepted Answer

Introduction / Context:The OSI model is a conceptual seven-layer framework created by ISO (International Organization for Standardization). It was developed to guide vendors and developers in building interoperable network protocols and to facilitate communication across heterogeneous networks. Given Data / Assumptions: The model is intended as a guideline, not an actual protocol suite. It standardizes how different network systems should communicate. We are considering the broad purpose, not implementation details. Concept / Approach: The main purpose of the OSI model is interoperability. Before OSI, vendor-specific networking protocols made cross-network communication difficult. OSI introduced a layered structure to simplify protocol design and allow independent development of each layer. This abstraction supports compatibility across different hardware and software. Step-by-Step Solution: Recognize that ISO created OSI to address interoperability issues.Understand that layers isolate functions, allowing independent upgrades.Conclude the key motivation was to enable different vendor systems to communicate. Verification / Alternative check: ISO's official documentation confirms interoperability and vendor neutrality as the primary goals. Why Other Options Are Wrong: Larger than DoD model: size comparison was not the purpose. Layer independence: a benefit, but not the main reason. Cisco adoption: Cisco did not create OSI. Replacement of TCP/IP: OSI never replaced TCP/IP; TCP/IP remains dominant. Common Pitfalls: Believing OSI is a protocol suite; it is a model, not an implementation. Final Answer: To enable communication between different types of networks and vendors

Question 13

Cisco IOS configuration management Which Cisco IOS command is used to save the current running configuration to the startup configuration, effectively creating a backup for the next reboot?

Accepted Answer

Introduction / Context:Cisco routers and switches store two main configuration files: the running configuration in RAM and the startup configuration in NVRAM. To preserve changes across reboots, administrators must save the running configuration to the startup configuration. Given Data / Assumptions: We are using Cisco IOS CLI commands. Objective: save changes permanently. Concept / Approach: The command copy running-config startup-config is the full IOS syntax to copy the current configuration into NVRAM. Shortcuts like wr mem exist but the canonical form is copy running-config startup-config. Step-by-Step Solution: Make desired changes in global configuration mode.Return to privileged EXEC mode.Execute: copy running-config startup-config.Verify with: show startup-config. Verification / Alternative check: Cisco documentation highlights this as the standard command, with wr mem being a legacy equivalent. Why Other Options Are Wrong: copy running backup: invalid syntax. config mem: not a valid Cisco IOS command. wr mem: works, but shorthand, not the canonical answer. save config: not standard in Cisco IOS. Common Pitfalls: Forgetting to save configuration, leading to loss after reboot. Confusing startup-config with running-config. Final Answer: copy running-config startup-config

Question 14

Cisco router CSU/DSU configuration If your router is functioning as a CSU/DSU and you want to provide a 64,000 bps serial link, which command must you enter?

Accepted Answer

Introduction / Context:When a Cisco router provides clocking on a serial connection (acting as a CSU/DSU), the clock rate command is required to set the data rate on the interface. This is typically used in lab environments or DCE (Data Communications Equipment) configurations. Given Data / Assumptions: The router is providing DCE clocking. Speed required = 64,000 bps (64 kbps). Command must be entered in interface configuration mode. Concept / Approach: The clock rate command configures the DCE interface's clock speed. The value is entered in bits per second. For 64,000 bps, the correct command is clock rate 64000. Step-by-Step Solution: Enter global configuration mode.Enter the serial interface configuration mode.Type: clock rate 64000.Verify with: show controllers serial to confirm DCE role. Verification / Alternative check: Cisco IOS reference guides confirm clock rate 64000 as the proper syntax for a 64 kbps link. Why Other Options Are Wrong: bandwidth 64 or 64000: sets bandwidth metric, not actual clocking. clock rate 64: incorrect unit (bps vs kbps). set speed: not a valid Cisco IOS command. Common Pitfalls: Confusing bandwidth (informational for routing protocols) with clock rate (actual line speed). Final Answer: RouterA(config-if)#clock rate 64000

Question 15

Spanning Tree Protocol and root bridge election In a switched network with many devices, how many root bridges are elected in a Spanning Tree Protocol (STP) topology?

Accepted Answer

Introduction / Context:Spanning Tree Protocol (STP) is used to prevent switching loops in a network by organizing switches into a loop-free logical topology. The root bridge plays a central role by acting as the reference point for path calculations. Given Data / Assumptions: We are considering a single spanning-tree instance (common in IEEE 802.1D). The network has dozens of switches. Concept / Approach: STP always elects exactly one root bridge per spanning-tree instance. All other switches calculate the shortest path to this root bridge. In PVST+ (Per-VLAN Spanning Tree), each VLAN has its own root bridge, but per instance the answer remains one. Step-by-Step Solution: Elect a single root bridge based on lowest bridge ID (priority + MAC).All switches exchange BPDUs to agree on the root.The rest of the topology converges around the root bridge. Verification / Alternative check: Cisco's STP documentation confirms: one root bridge per spanning-tree instance. Why Other Options Are Wrong: 2, 5, 12: arbitrary counts, incorrect. Depends on VLANs: true only when considering multiple VLANs, but in a single STP instance, it is always 1. Common Pitfalls: Forgetting that multiple VLANs can each have a root, leading to confusion. Final Answer: 1

Question 16

Frame Relay troubleshooting Which Cisco IOS command displays line status, protocol status, DLCI numbers, and LMI information for a Frame Relay interface?

Accepted Answer

Introduction / Context:Frame Relay was a WAN protocol widely used before MPLS. Troubleshooting Frame Relay requires verifying interface status, Data Link Connection Identifiers (DLCIs), and Local Management Interface (LMI) information. Cisco IOS provides specific commands for this purpose. Given Data / Assumptions: The protocol in use is Frame Relay. We want to check DLCI and LMI information. We are using Cisco IOS CLI commands. Concept / Approach: The show frame-relay pvc command provides detailed information about Frame Relay Permanent Virtual Circuits (PVCs). It displays DLCI status, interface statistics, and LMI status, making it the go-to command for verifying PVC operation. Step-by-Step Solution: Enter privileged EXEC mode.Type: show frame-relay pvc.Read DLCI, LMI, and PVC status outputs.Use this data to diagnose connectivity problems. Verification / Alternative check: Cisco's Frame Relay configuration and troubleshooting guides confirm this command as the standard for PVC/LMI info. Why Other Options Are Wrong: sh pvc: invalid abbreviation; not a standard IOS command. show interface: provides general interface status, but not detailed DLCI/LMI. show run: displays configuration, not runtime DLCI/LMI info. show controllers: shows hardware-level info, not PVC/LMI details. Common Pitfalls: Using show interface instead of show frame-relay pvc, leading to incomplete information. Final Answer: show frame-relay pvc

Question 17

Stub networks in routing: In computer networking and internetwork design, what is the best description of a stub network (i.e., a network that relies on a single path to reach all external destinations)?

Accepted Answer

Introduction / Context:A stub network is a foundational concept in routing. It describes a network segment that connects to the rest of the internetwork through a single router or single path. Understanding stub behavior helps you reason about default routes, summarization, and why certain dynamic routing protocol features are unnecessary in small, spoke-like topologies. Given Data / Assumptions: The question targets the definition of a stub network, not a stub Autonomous System or vendor-specific “stub area.” “Entry” and “exit” refer to the same single path to the broader internetwork. Traffic to and from the stub traverses one link to a single upstream device. Concept / Approach: A stub network has one way in and out. Because there is only one external connection, the local router typically advertises a default route downstream and may use static routing upstream or participate minimally in a dynamic protocol. No alternative external paths exist, so complex path selection or load sharing is irrelevant inside the stub. Step-by-Step Solution: Identify if multiple upstream paths exist. If there is exactly one, the network behaves as a stub.Map the single path to “one entry and exit point.” This captures ingress and egress being the same link.Conclude the correct description is the option that explicitly states “only one entry and exit point.” Verification / Alternative check: Examine routing tables and physical topology: a stub LAN will have a single default next hop to leave the LAN, and no additional equal-cost or backup external links. Traceroutes from hosts confirm every off-net path leaves via the same gateway. Why Other Options Are Wrong: More than one exit (A/B) implies multiple external paths, so it is not a stub. Only one entry and no exit (C) is illogical for bidirectional IP communication. Common Pitfalls: Confusing a “stub network” with an “OSPF stub area” (an OSPF design feature). Also, believing a stub cannot host servers—it can; the key is the single external path, not the role of endpoints. Final Answer: A network that has only one entry and exit point.

Question 18

Shared-hub bandwidth to a server: Ten users are connected to a classic hub operating at 10 Mbps half-duplex. The hub uplinks toward a switch, and a server on that switch also runs at 10 Mbps half-duplex. Assuming equal sharing on the collision domai…

Accepted Answer

Introduction / Context:This question tests understanding of classic Ethernet hubs, collision domains, and half-duplex contention. Unlike a switch, a hub is a multiport repeater: all connected devices share the same 10 Mbps bandwidth and contend for access using CSMA/CD. Knowing how sharing works helps estimate per-host throughput to a server. Given Data / Assumptions: Hub speed is 10 Mbps and half-duplex (collisions possible). Ten hosts are attached to the hub; traffic is destined to a 10 Mbps half-duplex server reachable through the hub’s uplink. Assume equal utilization and no QoS prioritization. Concept / Approach: On a hub, all ports form one collision domain and share the medium. Aggregate usable throughput among the contenders is bounded by 10 Mbps (less after CSMA/CD overhead). With roughly equal contention, a simple estimate divides the available rate by the number of active hosts. Step-by-Step Solution: Total shared bandwidth on the hub collision domain ≈ 10 Mbps.Ten equally active users share that capacity → effective share per host ≈ 10 Mbps / 10.Compute 10 / 10 = 1; therefore, each host gets ≈ 1 Mbps to the server under equal load. Verification / Alternative check: Packet captures show collisions and backoffs on a hub. Moving the users to a switch (separate collision domains per port) or increasing the server link rate changes the calculation. But with a hub, equal-share intuition matches lab measurements. Why Other Options Are Wrong: 10 Mbps (D) would require a dedicated, non-contended link per host (a switch), which is not the case. 2 Mbps (C) and 100 kbps (A) do not match equal sharing of 10 Mbps among ten users. Common Pitfalls: Forgetting that hubs do not isolate collisions; assuming full-duplex or switched behavior; ignoring protocol overheads (which only reduce throughput further from the 1 Mbps estimate). Final Answer: 1 Mbps

Question 19

Core function of VLANs on layer-2 switches: Which statement best describes what a Virtual LAN (VLAN) accomplishes in a switched internetwork?

Accepted Answer

Introduction / Context:VLANs logically segment a layer-2 network into multiple, isolated broadcast domains. This improves scalability, security, and traffic containment, and is fundamental to multi-tenant or multi-department designs in enterprise switching. Given Data / Assumptions: We are dealing with standard IEEE 802.1Q VLANs on switches. Collision domains are already per-port on modern switches. Broadcast containment is the primary design driver. Concept / Approach: Without VLANs, a layer-2 switch forwards broadcasts to all ports in the same VLAN, forming a single broadcast domain. Creating separate VLANs divides that broadcast domain so that ARP, DHCP DISCOVER, and unknown unicast flooding do not traverse between VLANs. Inter-VLAN communication requires a layer-3 device (router or L3 switch). Step-by-Step Solution: Identify the traffic type being controlled: broadcasts (and unknown unicasts).Associate VLANs with separate broadcast domains, each with its own IP subnet.Confirm that switching already gives one collision domain per port; VLANs do not “multiply collision domains on one port.” Verification / Alternative check: On a switch, run show vlan and observe that hosts in different VLANs do not see each other’s ARP broadcasts. Pinging across VLANs requires an SVI or router. Why Other Options Are Wrong: Fastest port (A) is unrelated to VLAN function. Multiple collision domains on one port (B) is incorrect; a single port is one collision domain. Multiple broadcast domains within a single collision domain (D) contradicts how switches operate. Common Pitfalls: Confusing collision domains (hub days) with broadcast domains; assuming VLANs provide security equal to firewalls (they help isolate but do not replace L3/L7 controls). Final Answer: Breaks up broadcast domains in a layer 2 switch internetwork.

Question 20

Switch trunking mechanisms: Which listed items are the encapsulation methods actually used to carry multiple VLANs across a trunk link on Ethernet switches?

Accepted Answer

Introduction / Context:Trunk links allow a single physical Ethernet connection to carry traffic for many VLANs. Two encapsulation methods historically provided this: IEEE 802.1Q (open standard) and ISL (Inter-Switch Link, Cisco proprietary and now largely deprecated). Understanding which technologies are true trunk encapsulations avoids misconfiguring VLAN management protocols as if they were trunks. Given Data / Assumptions: The list in the stem includes “VLAN Trunking Protocol,” “VLAN,” “802.1Q,” and “ISL,” implicitly as items 1–4. VTP is a VLAN database management protocol, not a trunk encapsulation. “VLAN” itself is not an encapsulation method. Concept / Approach: Real trunk encapsulations: 802.1Q (tags frames with a VLAN ID) and ISL (encapsulates frames, older Cisco proprietary). VTP distributes VLAN information across switches but does not tag or encapsulate user frames; it simply rides over an existing trunk. Step-by-Step Solution: Map items: 1=VTP, 2=VLAN, 3=802.1Q, 4=ISL.Identify encapsulations: items 3 and 4.Select the option corresponding to 3 and 4. Verification / Alternative check: On switches, trunk configuration shows encapsulation dot1q or isl (historically). VTP status is separate and independent from encapsulation choice. Why Other Options Are Wrong: Options involving 1 or 2 misclassify VTP or the concept “VLAN” as encapsulation methods. Common Pitfalls: Assuming enabling VTP “creates a trunk”; trunking must be configured (or negotiated) with protocols like DTP while encapsulation is 802.1Q/ISL. Final Answer: 3 and 4

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