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Question 461Question →

A network administrator is auditing network traffic generated by an automated asset tracking system. The system continuously sends brief location update bursts from handheld scanners to a central server using User Datagram Protocol (UDP). During peak operational hours, some location update packets are dropped due to network congestion, but the server does not request retransmissions. Which characteristic of UDP explains why packet retransmission is not automatically performed at the Transport layer?

Show answer & explanation

Answer: UDP is a connectionless protocol that does not establish session state or track packet delivery using sequence numbers and acknowledgments.

Answer

UDP is connectionless and does not maintain session state, sequence numbers, or transmission acknowledgments at the Transport layer.
The correct choice highlights that UDP is a connectionless protocol. It does not perform a connection handshake, track payload delivery, or assign sequence numbers to datagrams. Consequently, it operates with minimal header overhead and lower latency, leaving any error recovery or retransmission functions to the application layer if required.

Step-by-Step Solution

1
Analyze the operational requirements described in the scenario.
The application transmits continuous data bursts via UDP, prioritizing minimal overhead and latency, while accepting packet loss during congestion.
Understanding why packet loss occurs without automatic recovery requires analyzing UDP protocol header structures and behaviors.
2
Evaluate protocol features of UDP at Layer 4.
UDP features a minimal 8-byte header lacking sequence numbers, acknowledgment numbers, and window size fields.
Without these fields, UDP cannot track missing datagrams or negotiate retransmissions natively.
3
Differentiate connection-oriented and connectionless Transport layer behaviors.
TCP handles packet sequencing and retransmissions at Layer 4, whereas UDP delegates reliability concerns (if needed) entirely to upper-layer applications.
Connectionless protocols provide best-effort delivery without connection handshakes or state tracking.

Key Concept

Connectionless transport protocols prioritize low overhead by omitting connection setup, sequencing, and flow control mechanisms.
Question 462Question →

A network technician is troubleshooting a custom client-server application. Packet analysis confirms that IP routing and TCP port assignments are functioning properly. However, the receiving system fails to display text correctly because it cannot translate the incoming ASCII-encoded payload into the required UTF-8 format. At which layer of the OSI model does this data syntax translation occur?

Show answer & explanation

Answer: Presentation Layer

Answer

Presentation Layer
The correct answer identifies the Presentation Layer (Layer 6). This layer serves as a translator for the network, handling tasks such as character encoding conversion (e.g., ASCII to Unicode/UTF-8), data compression, and data encryption/decryption so that applications can correctly interpret the payload.

Step-by-Step Solution

1
Analyze the problem scenario to identify the specific failure.
The issue involves translating character encoding formats from ASCII to UTF-8.
Identifying the functional requirement (character translation/formatting) isolates the responsible network model layer.
2
Map data syntax translation to its corresponding OSI model layer.
Layer 6 (Presentation Layer) is responsible for syntax conversion, data formatting, encryption, and compression.
The Presentation Layer ensures that data sent from an application on one host can be parsed and understood by the application on another host.

Key Concept

OSI Model Presentation Layer Functions
Question 463Question →

A network workstation initiates an NTP time synchronization request to an external time server. Arrange the outbound protocol data unit (PDU) encapsulation steps in the correct order, starting from the application data generation down to physical transmission.

Drag items to arrange them in the correct order

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Answer

The correct sequence starts with creating a Layer 4 UDP segment, encapsulating it into a Layer 3 IP packet, wrapping it in a Layer 2 Ethernet frame with an FCS trailer, and finally converting the frame into Layer 1 physical signals.
During outbound network transmission, data moves down the protocol stack. The Application data is first encapsulated with a Transport layer (Layer 4) UDP header to form a Segment. Next, the Network layer (Layer 3) adds an IP header to create a Packet. Then, the Data Link layer (Layer 2) appends an Ethernet header and FCS trailer to create a Frame. Finally, the Physical layer (Layer 1) serializes the Frame into signals across the physical medium.

Step-by-Step Solution

1
Identify Layer 4 encapsulation
NTP data gets a UDP header, forming a Segment.
Outbound data travels down the OSI stack; the transport layer adds port information first.
2
Identify Layer 3 encapsulation
The UDP Segment receives an IP header, forming a Packet.
The network layer adds IP addressing for end-to-end routing.
3
Identify Layer 2 encapsulation
The IP Packet receives an Ethernet header and FCS trailer, forming a Frame.
The data link layer adds local MAC addresses and frame check sequence for hop-to-hop delivery.
4
Identify Layer 1 serialization
The Frame is converted into physical bits/signals.
The physical layer converts structured frames into signals for transmission on physical media.

Key Concept

Outbound OSI Encapsulation Sequence (Data -> Segment -> Packet -> Frame -> Bits)
Estimated Time:2m 0s
Question 464Question →

A network administrator is reviewing system protocol definitions to clarify layer responsibilities within the OSI model. Which of the following functions specifically operate at Layer 5 (the Session Layer)? (Select TWO.)

Select all that apply

Show answer & explanation

Answer: Establishing, maintaining, and gracefully terminating communication sessions between applications on distinct hosts; Controlling session dialogue modes (such as simplex, half-duplex, or full-duplex) and inserting synchronization checkpoints

Answer

The Session Layer (Layer 5) is responsible for establishing, managing, and terminating communication sessions between application entities, as well as managing dialogue control and inserting checkpoints into data streams.
Layer 5 (Session Layer) is dedicated to managing communication sessions between applications. Its primary duties include session setup, maintenance, and teardown, as well as dialogue control (duplex management) and checkpointing for session recovery.

Step-by-Step Solution

1
Analyze the core responsibilities of OSI Layer 5 (Session Layer).
Layer 5 coordinates the exchange of information between application sessions, managing session setup, teardown, dialogue mode, and synchronization checkpoints.
Differentiating Layer 5 from adjacent layers requires matching session control functions specifically to Layer 5.
2
Evaluate each provided option against OSI layer definitions.
Session establishment/termination and dialogue control belong to Layer 5. Encryption and data formatting belong to Layer 6. Segmentation and port-based flow control belong to Layer 4.
This confirms which options describe Layer 5 functions while identifying the mismapped adjacent layer functions.

Key Concept

OSI Layer 5 (Session Layer) Functions
Question 465Question →

A host computer on Subnet A transmits data to a server located on Subnet B through a Layer 3 router. As the data traverses the router to the destination network, which part of the Protocol Data Unit (PDU) is stripped and replaced with new addressing information at each hop?

Show answer & explanation

Answer: The Layer 2 frame header and trailer containing source and destination MAC addresses

Answer

The Layer 2 frame header and trailer containing source and destination MAC addresses
When a router forwards traffic between subnets, it de-encapsulates the incoming Layer 2 frame to extract the Layer 3 IP packet. After consulting its routing table for the next hop, it re-encapsulates the intact Layer 3 packet inside a brand-new Layer 2 frame with new source and destination MAC addresses appropriate for the next physical link.

Step-by-Step Solution

1
Identify the device performing the operation and its operating layer.
The router operates primarily at Layer 3 (Network Layer).
Routers make forwarding decisions based on destination IP addresses.
2
Analyze how encapsulation and de-encapsulation function during hop-by-hop routing.
When a router receives a frame, it de-encapsulates the Layer 2 frame, examines the Layer 3 packet IP header to find the next-hop interface, and re-encapsulates the IP packet into a new Layer 2 frame.
Layer 2 MAC addresses are local to individual broadcast domains and must be recreated for each physical subnet link.

Key Concept

Hop-by-hop Layer 2 re-framing during IP routing
Estimated Time:45s
Question 466Question →

Match each IP addressing and management service mechanism on the left with its primary functional purpose in an enterprise network on the right.

Click a left item, then click its matching right item

Items

DHCP Option 82
DNS SRV Record
IPAM Suite
NTP Stratum 1 Server

Matches

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Answer

DHCP Option 82 pairs with appending switch port and circuit metadata; DNS SRV Record pairs with publishing symbolic service names and port numbers; IPAM Suite pairs with centralizing tracking and allocation of address space; NTP Stratum 1 Server pairs with synchronizing time directly from hardware reference clocks.
Each IP addressing service component is accurately matched to its core technical definition: DHCP Option 82 appends circuit and switch port metadata at the relay agent; DNS SRV records resolve service instances and ports to hostnames; IPAM consolidates address inventory with DNS/DHCP administration; Stratum 1 NTP servers sync directly to physical reference timing devices.

Step-by-Step Solution

1
Analyze the functional role of DHCP Option 82
Identify that Relay Agent Information Option attaches layer 2 circuit and remote identifiers to relayed requests.
Relay agents add Option 82 headers so DHCP servers can make location-aware IP address assignments.
2
Analyze the functional role of DNS SRV records
Identify that SRV records contain protocol, service name, target hostname, priority, weight, and port assignments.
Services like Active Directory or VoIP rely on SRV records to discover server endpoints and service ports dynamically.
3
Analyze the functional role of IPAM software
Identify that IPAM orchestrates IP address inventory management with integrated DNS and DHCP services.
IPAM prevents IP address space collisions and provides auditing across multi-subnet environments.
4
Analyze the functional role of NTP Stratum levels
Identify that Stratum 1 devices attach directly to Stratum 0 physical timing standards.
Stratum 1 servers receive accurate time signals directly via dedicated hardware connections to reference timing sources.

Key Concept

Core operational roles and protocol characteristics of IP addressing, name resolution, network management, and clock synchronization services.
Question 467Question →

An automated logistics facility operates five separate warehouse buildings located within a single contiguous 200-acre industrial park owned by the company. The IT team must interconnect the core switches of all five buildings to support real-time inventory tracking with minimal latency. The design requires redundant paths so that if any single inter-building optical cable segment is severed, traffic automatically reroutes without disconnecting any building. However, budget constraints prevent installing dedicated fiber links between every possible building pair. Which network type classification and topology combination best satisfies these requirements?

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Answer: Campus Area Network (CAN) using a partial mesh topology

Answer

Campus Area Network (CAN) using a partial mesh topology
The deployment spans multiple buildings on a single corporate campus, placing it under the Campus Area Network (CAN) classification. To achieve fault tolerance against single fiber cuts while keeping costs within budget, a partial mesh topology is optimal because it provides redundant inter-building paths without requiring the expensive n(n−1)/2n(n-1)/2 links of a full mesh.

Step-by-Step Solution

1
Analyze the geographic scope of the deployment.
Connecting five buildings located within a single 200-acre corporate industrial park constitutes a Campus Area Network (CAN), as it spans multiple buildings across a contiguous, privately owned property.
Geographic network classifications are defined by physical extent: LAN is typically a single building, CAN covers multiple adjacent buildings on shared property, MAN covers a municipality, and WAN covers broad geographic regions.
2
Evaluate the redundancy and financial constraints for the physical topology.
A partial mesh topology provides multiple redundant interconnect pathways between critical nodes without requiring links between every possible node pair.
A full mesh topology for 5 nodes would require 10 dedicated links (n(n−1)/2n(n-1)/2), which violates the budget constraint. A star or bus topology lacks redundant links and creates single points of failure. A partial mesh balances cost with fault tolerance.
3
Synthesize the optimal network classification and topology choice.
Combining a CAN classification with a partial mesh topology fulfills both the geographic scope and high-availability criteria within budget limits.
This combination ensures continuous multi-building connectivity during single cable cuts while keeping installation costs reasonable.

Key Concept

Classification of network geographic scopes (CAN vs LAN/MAN/WAN) and selection of resilient physical topologies (Partial Mesh vs Full Mesh/Star/Bus).
Estimated Time:2m 0s
Question 468Question →

A network administrator needs to ensure that core infrastructure switches can automatically synchronize their system clocks with a centralized time server on the network. Which default port and transport protocol combination must be permitted through internal firewalls to allow Network Time Protocol (NTP) synchronization?

Show answer & explanation

Answer: UDP port 123

Answer

UDP port 123 is the standard port and transport protocol utilized by Network Time Protocol (NTP).
Network Time Protocol (NTP) uses UDP port 123 to provide clock synchronization across network-connected hardware. UDP is utilized because connection establishment overhead and TCP retransmissions would introduce latency variations that degrade timekeeping accuracy.

Step-by-Step Solution

1
Identify the required network service
The network service requested is Network Time Protocol (NTP), which synchronizes device clocks across a IP network.
Accurate timestamps across devices are essential for logging and event correlation.
2
Determine the transport protocol and port number for NTP
NTP standardized operations run on User Datagram Protocol (UDP) on well-known port 123.
UDP is chosen for NTP to avoid connection-establishment delays and retransmission delays that could distort time synchronization math.

Key Concept

Standard Network Port Assignments (NTP)
Question 469Question →

A network administrator is configuring inbound ACL rules on an edge firewall. The security baseline requires enabling secure, encrypted command-line management for distant switches while allowing internal infrastructure devices to synchronize their clocks against an external stratum-1 time server. Which TWO of the following port and transport protocol combinations must be permitted in the firewall policy? (Select TWO)

Select all that apply

Show answer & explanation

Answer: TCP port 22; UDP port 123

Answer

The required services are Secure Shell (SSH), which operates over TCP port 22, and Network Time Protocol (NTP), which operates over UDP port 123.
Secure Shell (SSH) provides secure, encrypted command-line sessions using TCP port 22. Network Time Protocol (NTP) synchronizes system clocks across network devices using connectionless UDP port 123.

Step-by-Step Solution

1
Determine the protocol and port required for secure remote command-line access.
SSH (Secure Shell) meets the requirement for encrypted terminal access and runs on TCP port 22.
Telnet operates on TCP port 23 but sends credentials and payload in unencrypted cleartext.
2
Determine the protocol, port, and transport layer for system clock synchronization.
NTP (Network Time Protocol) synchronizes device clocks using UDP port 123.
NTP requires low-overhead, latency-sensitive transport and is defined to run over connectionless UDP rather than TCP.

Key Concept

Port number and transport protocol mapping for SSH (TCP 22) and NTP (UDP 123).
Question 470Question →

Match each core IP addressing service or protocol feature on the left with its primary function or use case on the right.

Click a left item, then click its matching right item

Items

DHCP Relay Agent
DNS PTR Record
IP Address Management (IPAM)
NTP Stratum 1 Server

Matches

Show answer & explanation

Answer

DHCP Relay Agent matches forwarding broadcast messages across routers; DNS PTR Record matches mapping IP addresses to domain names for reverse resolution; IP Address Management (IPAM) matches centralized tracking of subnet utilization and allocations; NTP Stratum 1 Server matches synchronizing directly from a primary reference clock like GPS.
Each IP service maps directly to its specialized administrative role: DHCP relay agents enable multi-VLAN IP leasing across routers, PTR records implement reverse DNS resolution, IPAM centralizes address space tracking, and Stratum 1 NTP servers sync directly with physical reference time sources.

Step-by-Step Solution

1
Analyze the primary operation of a DHCP Relay Agent.
Routers drop client DHCP broadcasts by default. A relay agent receives these broadcasts on a local VLAN and forwards them to a remote server.
Enables centralizing DHCP servers across multiple VLANs without putting a server in every subnet.
2
Determine the function of a DNS PTR record.
PTR records perform reverse name resolution by mapping IP addresses back to domain names.
Forward DNS zones map names to IP addresses (A/AAAA records), whereas reverse DNS zones store PTR records.
3
Identify the role of IPAM in enterprise networks.
IPAM centralizes address space planning, tracks static and dynamic assignments, and monitors pool depletion.
Consolidates management across DNS, DHCP, and IP address inventory to prevent conflicts and track utilization.
4
Evaluate NTP Stratum hierarchy levels.
Stratum 1 servers attach directly to physical Stratum 0 time sources.
Stratum 0 represents high-precision hardware clocks (GPS/atomic), making directly attached network time servers Stratum 1.

Key Concept

Core IP Addressing Services
Question 471Question →

A system administrator observes syslog messages being sent from a local host to a remote log server. As the outgoing syslog data passes down the host's protocol stack during encapsulation, which of the following actions occur? (Select TWO.)

Select all that apply

Show answer & explanation

Answer: The Transport layer encapsulates the syslog payload into a segment or datagram by adding transport port headers.; The Network layer encapsulates the transport data unit into a packet by adding source and destination IP addresses.

Answer

During outbound encapsulation, the Transport layer appends transport port headers to create a segment/datagram, and the Network layer appends IP addresses to form a packet.
Outbound encapsulation works down the protocol stack. The Transport layer adds port headers to form segments or datagrams, and the Network layer adds IP headers to form packets.

Step-by-Step Solution

1
Analyze Layer 4 processing during outbound encapsulation.
Application payload (syslog data) receives a Transport layer header with source and destination ports.
Layer 4 handles process-to-process communication by prepending port addresses.
2
Analyze Layer 3 processing during outbound encapsulation.
The resulting Transport datagram receives a Network layer header containing source and destination IP addresses.
Layer 3 handles host-to-host logical routing across network boundaries.

Key Concept

Outbound Encapsulation Sequence and Protocol Data Units
Estimated Time:45s
Question 472Question →

A network technician needs to configure a DNS server to enable hostnames to be resolved from known IP addresses during network troubleshooting and log auditing. Which DNS record type should be created to support this reverse lookup functionality?

Show answer & explanation

Answer: PTR record

Answer

PTR record
PTR (Pointer) records provide reverse DNS resolution by mapping IP addresses back to fully qualified domain names.

Step-by-Step Solution

1
Analyze the service requirement
The target requirement is resolving a host's domain name starting from an IP address (reverse DNS lookup).
Understanding whether the operational need is forward or reverse resolution determines the record type.
2
Select the appropriate DNS resource record type
PTR records store mapping entries specifically for reverse DNS resolution.
Forward records (A/AAAA) convert names to IP addresses, while PTR records map IP addresses to canonical hostnames.

Key Concept

DNS Reverse Lookup and PTR Records
Question 473Question →

Host A (IP address 10.1.10.45/24) is connected to an access port assigned to VLAN 10 on a Layer 2 switch. Host B (IP address 10.1.20.80/24) is connected to another access port assigned to VLAN 20 on the same switch. Host A attempts to send a packet to Host B, causing Host A to broadcast an ARP request for Host B's IP address. No Layer 3 router or Layer 3 switch interface is configured on the network. How does the Layer 2 switch process the incoming ARP broadcast frame?

Show answer & explanation

Answer: The switch floods the ARP broadcast frame exclusively to operational ports assigned to VLAN 10, preventing Host B from receiving the request.

Answer

The switch floods the ARP broadcast frame exclusively to operational ports assigned to VLAN 10, preventing Host B from receiving the request.
VLANs create distinct Layer 2 broadcast domains. When Host A generates an ARP broadcast request on VLAN 10, the Layer 2 switch floods the frame only out of ports assigned to VLAN 10. Since Host B is on VLAN 20 and no Layer 3 routing device exists to route traffic between the subnets, Host B will never receive the ARP request.

Step-by-Step Solution

1
Identify the ingress port and VLAN membership of the sender.
Host A is connected to an access port assigned to VLAN 10, placing its generated frames inside VLAN 10's broadcast domain.
Layer 2 switches associate incoming frames on access ports with the port's assigned VLAN ID.
2
Analyze frame destination MAC address and switch forwarding rules.
An ARP request uses the Layer 2 broadcast destination address (FF:FF:FF:FF:FF:FF). The switch floods broadcast frames to all active ports within the ingress VLAN.
Broadcast frames must be sent to all members of the broadcast domain, but VLAN boundaries strictly limit the scope of the flood.
3
Evaluate inter-VLAN reachability without a Layer 3 gateway.
Because Host B is on VLAN 20 and no router/Layer 3 device is present, the broadcast frame never reaches Host B, and inter-VLAN communication fails.
VLANs act as logically independent switch instances at Layer 2 and require Layer 3 routing (Router-on-a-Stick or Layer 3 switch SVI) to forward traffic between different subnets/VLANs.

Key Concept

VLAN Broadcast Domain Isolation
Estimated Time:1m 30s
Question 474Question →

A network technician is configuring an interface access list on a router to allow secure, encrypted command-line management connections to a remote Linux server. Which transport protocol and port combination must be permitted to allow Secure Shell (SSH) traffic?

Show answer & explanation

Answer: TCP port 22

Answer

TCP port 22 is the standard port and protocol for Secure Shell (SSH) remote management traffic.
Secure Shell (SSH) uses TCP port 22 by default to provide secure, encrypted command-line management traffic over a connection-oriented session.

Step-by-Step Solution

1
Identify the application protocol requested in the scenario.
The scenario specifies Secure Shell (SSH) for encrypted command-line management.
Determining the target application protocol is necessary to select the correct transport protocol and port number.
2
Determine the transport layer protocol requirement.
SSH requires a reliable, connection-oriented session provided by TCP.
Interactive terminal communications rely on error checking and session establishment.
3
Map SSH to its well-known default port number.
SSH uses TCP port 22 by default.
IANA assigns port 22 specifically for secure terminal access via SSH.

Key Concept

Standard Default Ports and Protocols
Estimated Time:45s
Question 475Question →

A network administrator is creating a new subnet dedicated to a small group of administrative servers using the IPv4 prefix length /28/28. What is the maximum number of usable host IP addresses available for devices within this subnet?

Show answer & explanation

Answer: 14

Answer

14 usable host IP addresses
With a /28/28 prefix, 44 bits remain for the host portion (32−28=432 - 28 = 4). The total number of IP addresses is 24=162^4 = 16. Because the network address (all host bits 0) and the broadcast address (all host bits 1) cannot be assigned to hosts, subtracting 22 yields exactly 1414 usable host IP addresses.

Step-by-Step Solution

1
Determine the number of host bits
32−28=432 - 28 = 4 host bits
An IPv4 address consists of 3232 bits. Subtracting the prefix length leaves the host portion of the address.
2
Calculate total IP addresses in the subnet
24=162^4 = 16 total IP addresses
The total number of IP addresses in a CIDR block is calculated as 2host bits2^{\text{host bits}}.
3
Subtract reserved addresses to find usable host IP count
16−2=1416 - 2 = 14 usable host IPs
The first address (network ID) and the last address (broadcast address) cannot be assigned to individual host interfaces.

Key Concept

IPv4 Subnet Usable Host Capacity Calculation
Question 476Question →

A network administrator connects Switch-A (Root Bridge) to Switch-B using two parallel 10 Gbps Ethernet links for path redundancy. The connections are established as follows:
- Link 1 connects Switch-A port Gi1/0/1 to Switch-B port Gi1/0/1.
- Link 2 connects Switch-A port Gi1/0/2 to Switch-B port Gi1/0/2.

On Switch-A, port Gi1/0/1 uses the default port priority of 128, while port Gi1/0/2 is manually configured with a port priority of 64. On Switch-B, port Gi1/0/1 is manually configured with a port priority of 32, while port Gi1/0/2 retains the default port priority of 128.

Assuming all other Spanning Tree Protocol (STP) parameters remain default and both links are operational, which interface on Switch-B will be selected as the Root Port, and why?

Show answer & explanation

Answer: Interface Gi1/0/2, because it receives BPDUs from Switch-A with a lower sender port priority.

Answer

Interface Gi1/0/2 will be elected as the Root Port on Switch-B because it receives BPDUs containing a lower upstream (Designated) port priority value (64) from Switch-A.
When a non-root switch has multiple equal-cost paths to the Root Bridge originating from the same upstream switch, Root Port selection is determined by evaluating the upstream sender's Port ID (Port Priority + Port Index). Switch-A transmits BPDUs out of Gi1/0/2 with a port priority of 64, which is lower than the default priority of 128 sent out of Gi1/0/1. Switch-B receives this lower value on its Gi1/0/2 interface and selects it as the Root Port.

Step-by-Step Solution

1
Evaluate the Root Port decision criteria sequence for Switch-B.
Switch-B compares incoming BPDUs on Gi1/0/1 and Gi1/0/2 using the standard STP tie-breaker hierarchy.
Non-root switches must select exactly one Root Port facing the Root Bridge.
2
Compare Root Path Cost and Designated Bridge ID.
Both ports receive BPDUs from the same Root Bridge (Switch-A) over identical 10 Gbps links, resulting in a tie for both criteria.
Both links connect directly between Switch-A and Switch-B at identical speed.
3
Evaluate the Designated (sender) Port ID tie-breaker.
Switch-A transmits BPDUs with Port ID 128.1 on link 1 and Port ID 64.2 on link 2.
Port ID consists of Port Priority + Port Number. Switch-A port Gi1/0/2 advertises a priority of 64, which is lower than 128.
4
Select the Root Port based on lowest Designated Port ID.
Switch-B port Gi1/0/2 receives the BPDU with the lower Designated Port ID (64.2) and becomes the Root Port.
Lower numerical values take precedence in STP decision processes.

Key Concept

STP Root Port Selection & Designated Sender Port ID Tie-Breakers
Estimated Time:1m 30s
Question 477Question →

A network administrator connects two Layer 2 switches using an 802.1Q trunk link. Switch A has native VLAN 10 configured on its trunk port, while Switch B has native VLAN 20 configured on its trunk port. Host A, attached to an access port in VLAN 10 on Switch A, sends a broadcast frame. Switch A transmits this frame untagged across the trunk link. Which of the following best describes how Switch B processes this incoming untagged frame?

Show answer & explanation

Answer: Switch B assigns the incoming untagged frame to its local native VLAN (VLAN 20) and forwards it to all active access ports in VLAN 20.

Answer

Switch B assigns the incoming untagged frame to its local native VLAN (VLAN 20) and forwards it to all active access ports in VLAN 20.
Under 802.1Q trunking specifications, frames belonging to the native VLAN are sent across the trunk untagged. When an untagged frame arrives at a receiving switch interface, that switch implicitly tags or assigns the frame to its own locally configured native VLAN. Because Switch A sends VLAN 10 traffic untagged and Switch B has native VLAN 20 configured, Switch B maps the incoming untagged frame into VLAN 20, causing cross-VLAN traffic leakage.

Step-by-Step Solution

1
Analyze how Switch A transmits VLAN 10 traffic across the trunk link.
Because VLAN 10 is configured as the native VLAN on Switch A's trunk port, Switch A strips the 802.1Q tag and sends the frame untagged across the link.
802.1Q trunking rules dictate that frames belonging to the port's native VLAN are sent without an explicit 802.1Q VLAN header.
2
Determine how Switch B interprets untagged ingress frames on its trunk port.
Switch B receives the untagged frame and associates it with its own configured native VLAN, which is VLAN 20.
A switch interface assigned an 802.1Q native VLAN treats any incoming frame without a VLAN tag as member traffic of that local native VLAN.
3
Evaluate the forwarding destination of the broadcast frame on Switch B.
Switch B floods the broadcast frame out all active interfaces belonging to VLAN 20.
Broadcast frames are flooded throughout their assigned Layer 2 broadcast domain.

Key Concept

802.1Q Native VLAN Operation and Mismatch Behavior
Question 478Question →

A network administrator is configuring Layer 2 switching features and security controls across an enterprise switch environment. Match each switching concept or operational mechanism on the left to its corresponding functional behavior on the right.

Click a left item, then click its matching right item

Items

802.1Q Native VLAN
STP PortFast
BPDU Guard
Dynamic MAC Aging

Matches

Show answer & explanation

Answer

802.1Q Native VLAN matches untagged traffic transport across trunk links; STP PortFast matches direct transition to forwarding state; BPDU Guard matches err-disabling ports upon BPDU reception; Dynamic MAC Aging matches flushing idle CAM table entries.
Each feature is correctly mapped to its core Layer 2 switching mechanism: the 802.1Q native VLAN handles untagged trunk traffic, PortFast accelerates edge port transition to forwarding, BPDU Guard protects edge ports by err-disabling them when BPDUs are detected, and dynamic MAC aging clears inactive CAM table entries.

Step-by-Step Solution

1
Analyze the role of the 802.1Q Native VLAN.
Identified that native VLANs handle traffic that does not contain an 802.1Q tag across a trunk link.
By default in 802.1Q trunking, frames belonging to the native VLAN are sent untagged.
2
Analyze the function of STP PortFast.
Identified immediate forwarding state transition on end-user access ports.
PortFast is intended for edge ports so end-user clients do not experience DHCP or connection timeouts while waiting for STP listening/learning phases.
3
Analyze the operation of BPDU Guard.
Identified err-disable port state reaction upon receiving BPDUs.
Edge ports should not receive BPDUs from other switches; receiving one indicates a potential rogue switch or loop risk.
4
Analyze the function of Dynamic MAC Aging.
Identified purging of idle MAC addresses from the switch's CAM table.
Switches use an aging timer to clear inactive MAC addresses to ensure frame forwarding remains efficient and accurate.

Key Concept

Switching Concepts and VLANs
Question 479Question →

A security log server receives an incoming transmission containing a syslog message sent from a remote network gateway. As the destination host network stack processes this data unit through de-encapsulation, which transformation occurs specifically at Layer 3 immediately before payload processing is handed off to Layer 4?

Show answer & explanation

Answer: The IPv4 header is inspected and stripped, converting the Layer 3 packet into a Layer 4 UDP datagram containing source and destination port parameters.

Answer

The IPv4 header is inspected and stripped, converting the Layer 3 packet into a Layer 4 UDP datagram containing source and destination port parameters.
During inbound de-encapsulation on a receiving host, each layer inspects its corresponding control header, performs integrity and address checks, and strips its header before passing the encapsulated payload upward. At Layer 3 (Network Layer), the host inspects the IP header, verifies the IP destination address, and removes the IP header. The remaining payload is a Layer 4 PDU (a UDP datagram containing source and destination port numbers), which is passed to Layer 4 for transport processing.

Step-by-Step Solution

1
Identify the OSI layer processing boundary described in the scenario
The scenario focuses on the specific de-encapsulation step occurring at Layer 3 (Network Layer) moving toward Layer 4 (Transport Layer).
De-encapsulation unwraps data headers sequentially from Layer 1 up to Layer 7.
2
Determine the PDU state at Layer 3
Layer 3 receives an IP packet from Layer 2 after the Ethernet header and trailer have been removed.
The Data Link layer strips Layer 2 framing before passing the enclosed packet to the Network layer.
3
Analyze Layer 3 processing actions
Layer 3 validates fields in the IP header (such as destination IP and Protocol identifier 17 for UDP), strips the IP header, and forwards the resulting Layer 4 segment/datagram to the Transport layer.
Stripping the Layer 3 header reveals the Layer 4 PDU (UDP datagram).

Key Concept

De-encapsulation PDU Transformations across OSI Layers
Estimated Time:2m 0s
Question 480Question →

Match each OSI model layer on the left with its primary operational function and corresponding Protocol Data Unit (PDU) characteristics on the right.

Click a left item, then click its matching right item

Items

Data Link Layer (Layer 2)
Network Layer (Layer 3)
Transport Layer (Layer 4)
Presentation Layer (Layer 6)

Matches

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Answer

The Data Link Layer (Layer 2) pairs with node-to-node frame delivery via MAC addresses; the Network Layer (Layer 3) pairs with packet routing via IP addresses; the Transport Layer (Layer 4) pairs with end-to-end process multiplexing via segments and ports; and the Presentation Layer (Layer 6) pairs with syntax translation, compression, and encryption.
Each OSI layer serves a specific purpose in network communications: Layer 2 uses Frames and MAC addresses for local transmission; Layer 3 uses Packets and IP addresses for routing; Layer 4 uses Segments and port numbers for transport multiplexing; and Layer 6 provides data translation, compression, and encryption.

Step-by-Step Solution

1
Analyze Layer 2 (Data Link Layer) characteristics.
Layer 2 builds Frames using MAC addressing for physical network segment communication.
Hardware addressing and framing are defined at the Data Link Layer.
2
Analyze Layer 3 (Network Layer) characteristics.
Layer 3 manages Packets and IP routing across subnets.
Path selection and logical addressing occur at the Network Layer.
3
Analyze Layer 4 (Transport Layer) characteristics.
Layer 4 uses Segments and port numbers for end-to-end communication.
Process-to-process communication and multiplexing are handled by TCP/UDP at the Transport Layer.
4
Analyze Layer 6 (Presentation Layer) characteristics.
Layer 6 performs encryption, compression, and format conversion.
Data syntax standardization between sender and receiver occurs at the Presentation Layer.

Key Concept

OSI Layer Functions and PDU Mapping
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