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CNPA practice questions

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Question 1Network Fundamentals and Models

In the TCP/IP model, which layer is responsible for logical addressing and routing of packets between networks?

  1. Internet layer Correct answer.
  2. Transport layer
  3. Application layer
  4. Network access layer

Explanation

The Internet layer handles logical addressing, packet encapsulation, and path selection between networks, which is why IP addresses and routers operate at this layer. The transport layer deals with end-to-end delivery, while the network access layer covers the local link.

Question 2Network Fundamentals and Models

Which OSI layer is responsible for establishing, managing, and terminating sessions between applications?

  1. Transport layer
  2. Application layer
  3. Session layer Correct answer.
  4. Presentation layer

Explanation

The session layer (Layer 5) opens, maintains, and closes dialogue between two hosts, including checkpointing and recovery. The presentation layer handles data format translation and encryption, and the transport layer handles segmentation and reliability.

Question 3Network Fundamentals and Models

Which protocol operates at the transport layer and provides connection-oriented, reliable delivery?

  1. UDP
  2. ARP
  3. ICMP
  4. TCP Correct answer.

Explanation

TCP is connection-oriented: it uses a three-way handshake, sequence numbers, and acknowledgments to guarantee ordered, reliable delivery. UDP is connectionless, while ICMP and ARP operate at the network and link levels respectively.

Question 4Network Fundamentals and Models

A network uses the address 192.168.10.0/24. Which address is the directed broadcast address for this subnet?

  1. 192.168.10.254
  2. 192.168.10.0
  3. 192.168.10.255 Correct answer.
  4. 192.168.10.1

Explanation

With a /24 mask, the host portion occupies the last octet, so the broadcast address sets all host bits to 1, which is 192.168.10.255. The .0 address is the network address and .254 is the highest usable host.

Question 5Network Fundamentals and Models

Which device forwards frames based on MAC addresses within a single broadcast domain?

  1. Firewall
  2. Layer 2 switch Correct answer.
  3. Hub
  4. Router

Explanation

A Layer 2 switch builds a MAC address table and forwards frames only out the port associated with the destination MAC, keeping traffic within one broadcast domain. A router moves packets between broadcast domains using IP addresses.

Question 6Network Fundamentals and Models

Which cable type uses twisted pairs and an RJ-45 connector for Ethernet LAN connections?

  1. Cat 6 UTP Correct answer.
  2. Coaxial cable
  3. Single-mode fiber
  4. Multimode fiber

Explanation

Cat 6 UTP is unshielded twisted-pair copper cabling terminated with RJ-45 connectors, commonly used for Gigabit Ethernet. Fiber types use optical connectors such as LC or SC, and coaxial uses BNC or F-type connectors.

Question 7Network Fundamentals and Models

What is the primary purpose of DNS in a network?

  1. Routing packets between subnets
  2. Resolving host names to IP addresses Correct answer.
  3. Encrypting web traffic
  4. Assigning IP addresses automatically

Explanation

DNS is a hierarchical naming system that maps human-readable domain names to IP addresses so clients can reach the correct server. DHCP handles automatic address assignment, and routing is a Layer 3 function.

Question 8Network Fundamentals and Models

Which IPv4 address range is reserved for private use according to RFC 1918?

  1. 172.16.0.0 to 172.31.255.255 Correct answer.
  2. 169.254.0.0 to 169.254.255.255
  3. 224.0.0.0 to 239.255.255.255
  4. 192.0.2.0 to 192.0.2.255

Explanation

RFC 1918 defines the private ranges 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16, so 172.16.0.0 through 172.31.255.255 is private. The other ranges serve documentation, link-local, and multicast purposes.

Question 9Network Fundamentals and Models

Which port does a client typically use to send an HTTP request to a web server?

  1. 25
  2. 53
  3. 443
  4. 80 Correct answer.

Explanation

Plain HTTP listens on TCP port 80 by default, so a client connects to destination port 80 on the server. Port 443 is HTTPS, 53 is DNS, and 25 is SMTP.

Question 10Network Fundamentals and Models

A host with address 10.5.20.130/26 needs to reach a server at 10.5.20.200. What happens at the routing decision point?

  1. The host ARPs directly for the server because both addresses share a subnet
  2. The host drops the packet because the /26 mask is invalid
  3. The host sends an ICMP redirect to the server
  4. The host forwards the packet to its default gateway because the destination is outside its subnet Correct answer.

Explanation

A /26 mask yields subnets of 64 addresses, so 10.5.20.130/26 covers .128 through .191. The server at .200 lies in the next subnet (.192-.255), so the host must send the frame to its default gateway.

Question 11Network Fundamentals and Models

Which statement correctly describes the difference between a collision domain and a broadcast domain?

  1. A collision domain spans routers, while a broadcast domain is limited to one switch port
  2. Collision domains apply only to fiber links, and broadcast domains apply only to copper
  3. A collision domain contains frames that can collide, while a broadcast domain contains all devices that receive a broadcast frame Correct answer.
  4. A broadcast domain is always smaller than a collision domain

Explanation

A collision domain is the set of devices sharing a medium where frames can collide, and a broadcast domain is the set of devices reached by a Layer 2 broadcast. Switches break up collision domains per port but keep one broadcast domain until a router or VLAN separates it.

Question 12Network Fundamentals and Models

What is the main function of ARP on an Ethernet network?

  1. Mapping a known IPv4 address to the corresponding MAC address Correct answer.
  2. Encrypting payloads at the link layer
  3. Translating private addresses to public addresses
  4. Discovering neighboring routers with hello packets

Explanation

ARP broadcasts a request asking which MAC owns a given IPv4 address, and the owner replies with its hardware address so the frame can be encapsulated. NAT handles address translation, and routing protocols discover routers.

Question 13Network Fundamentals and Models

Which characteristic distinguishes UDP from TCP when supporting a real-time voice application?

  1. UDP guarantees ordered delivery through sequence numbers
  2. UDP provides built-in congestion control
  3. UDP performs a three-way handshake before sending data
  4. UDP avoids retransmission delays, accepting some loss to keep latency low Correct answer.

Explanation

Voice traffic tolerates small losses better than added delay, so UDP's connectionless, no-retransmission behavior suits real-time media. TCP's handshake, ordering, and retransmissions add latency that harms voice quality.

Question 14Network Fundamentals and Models

A technician must connect two switches in different buildings 500 meters apart with high immunity to electromagnetic interference. Which medium is most appropriate?

  1. Coaxial thinnet
  2. Multimode fiber Correct answer.
  3. Cat 5e UTP
  4. Cat 6a STP

Explanation

Multimode fiber supports distances well beyond copper limits and is immune to electromagnetic interference because it carries light. Copper options such as Cat 5e and Cat 6a are limited to roughly 100 meters and can pick up EMI.

Question 15Network Fundamentals and Models

Which address does a DHCP client use as the source when it first broadcasts a DISCOVER message?

  1. 255.255.255.255
  2. The address of the DHCP relay
  3. 0.0.0.0 Correct answer.
  4. 127.0.0.1

Explanation

Before it has a lease, the client has no valid IP, so it uses 0.0.0.0 as the source and 255.255.255.255 as the destination for the initial broadcast. The DHCP relay address is a destination used by relays, not by the client source.

Question 16Network Fundamentals and Models

Which protocol provides a loop-free Layer 2 topology by electing a root bridge and blocking redundant ports?

  1. VRRP
  2. OSPF
  3. STP Correct answer.
  4. LACP

Explanation

Spanning Tree Protocol elects a root bridge and places redundant ports into a blocking state to prevent Layer 2 loops. OSPF and VRRP are Layer 3 protocols, and LACP bundles links rather than blocking them.

Question 17Network Fundamentals and Models

Which IPv6 address type is used for one-to-many delivery to the nearest group member and is commonly used for router discovery?

  1. Multicast Correct answer.
  2. Anycast
  3. Unicast
  4. Broadcast

Explanation

IPv6 uses multicast for one-to-many delivery, and the all-routers multicast address ff02::2 supports router discovery. IPv6 has no broadcast type, and anycast delivers to one of several nodes based on routing proximity.

Question 18Network Fundamentals and Models

A packet arrives at a router with a destination address not present in its routing table and no default route configured. What does the router do?

  1. It holds the packet until a route appears
  2. It forwards the packet to the lowest-metric neighbor
  3. It drops the packet and may return an ICMP destination unreachable message Correct answer.
  4. It floods the packet out all interfaces

Explanation

Without a matching route or default route, the router has no path, so it discards the packet and typically sends ICMP destination unreachable back to the source. Routers never flood unknown unicast destinations at Layer 3.

Question 19Network Fundamentals and Models

Which field in an Ethernet II frame indicates the upper-layer protocol being carried?

  1. EtherType Correct answer.
  2. FCS
  3. Source MAC
  4. Preamble

Explanation

The EtherType field, such as 0x0800 for IPv4 or 0x86DD for IPv6, tells the receiver which protocol is encapsulated in the payload. The preamble synchronizes the link, and the FCS detects errors.

Question 20Network Fundamentals and Models

A network administrator sees the subnet 192.168.4.0/22. Which range of addresses belongs to this subnet?

  1. 192.168.4.0 to 192.168.4.255
  2. 192.168.4.0 to 192.168.5.255
  3. 192.168.4.0 to 192.168.7.255 Correct answer.
  4. 192.168.4.0 to 192.168.15.255

Explanation

A /22 mask leaves 10 host bits, giving 1,024 addresses, so the block spans 192.168.4.0 through 192.168.7.255. The third octet increments by four because the block size in that octet is four.

Question 21Network Fundamentals and Models

Which statement best explains why a VLAN improves network segmentation on a single switch?

  1. It creates separate broadcast domains without requiring additional physical switches Correct answer.
  2. It eliminates the need for a router between VLANs
  3. It increases the link speed between connected hosts
  4. It encrypts frames between VLAN members

Explanation

A VLAN logically divides one physical switch into multiple broadcast domains, containing broadcasts and improving security and performance. Inter-VLAN traffic still requires a Layer 3 device such as a router or multilayer switch.

Question 22Network Fundamentals and Models

An engineer observes that a TCP sender reduces its congestion window after detecting packet loss. Which mechanism is being applied?

  1. Congestion control through slow start and multiplicative decrease Correct answer.
  2. Name resolution through DNS caching
  3. Address translation through NAT
  4. Frame filtering through an access control list

Explanation

TCP congestion control uses slow start to grow the window and multiplicative decrease to shrink it when loss signals congestion. This keeps the sender from overwhelming the path and is distinct from naming, translation, or filtering functions.

Question 23Network Fundamentals and Models

A host sends a packet to 224.0.0.5. How is this traffic handled at Layer 2 on a typical Ethernet LAN?

  1. It is converted to a unicast frame for the default gateway
  2. It is dropped because 224.0.0.5 is not routable
  3. It is broadcast to every host on the LAN
  4. It is mapped to a multicast MAC address and delivered only to hosts that joined the group Correct answer.

Explanation

224.0.0.5 is the OSPF all-routers multicast address. IPv4 multicast maps to the 01:00:5e MAC prefix, and switches forward it only to ports where hosts have joined the group via IGMP.

Question 24Network Fundamentals and Models

Which design outcome results from placing a router between two Layer 2 segments that each contain many hosts?

  1. Both segments merge into one collision domain
  2. MAC address tables are shared between the segments
  3. Broadcast traffic is forwarded to both segments by default
  4. Each segment keeps its own broadcast domain, and broadcasts do not cross the router Correct answer.

Explanation

Routers do not forward Layer 2 broadcasts by default, so each attached segment remains a separate broadcast domain. This limits broadcast scope and is a core reason for hierarchical network design.

Question 25Network Fundamentals and Models

A network uses NAT overload on a border router. Which information allows the router to return replies to the correct internal host?

  1. The DNS name of the internal host
  2. The TTL value in the IP header
  3. The destination MAC address of each reply
  4. A translation table that tracks source IP, source port, and protocol Correct answer.

Explanation

NAT overload, or PAT, distinguishes internal sessions by the combination of source address, source port, and protocol stored in the translation table. Replies are matched against that table and rewritten back to the original internal host.

Question 26Network Fundamentals and Models

A packet is forwarded across a routed network. Which statement correctly describes how the OSI model handles encapsulation as the packet moves down the stack and onto the wire?

  1. Each layer adds its own header to the payload received from the layer above, and the receiving host removes headers in reverse order. Correct answer.
  2. The transport layer encapsulates the network header, which in turn encapsulates the data-link header.
  3. Headers are added only at the physical layer because the upper layers operate purely in software.
  4. Each layer replaces the header of the layer above so that only one header exists in the frame.

Explanation

Encapsulation is cumulative: the transport layer hands a segment to the network layer, which prepends a network header, and the data-link layer prepends a frame header and trailer before bits are transmitted. The receiving stack performs decapsulation in the reverse order, each layer stripping only its own header and passing the payload upward. This layering lets each layer serve the one above it without depending on the internal details of that layer.

Question 27Network Fundamentals and Models

A workstation must send a single stream of data to a specific group of subscribed receivers, and the sender wants the network to replicate packets only where the distribution tree branches. Which delivery model should be selected?

  1. Unicast, with the sender opening a separate connection to each receiver
  2. Anycast, with the packet delivered to the topologically nearest member
  3. Broadcast, with the packet flooded to every host in the subnet
  4. Multicast, with receivers joining a group address Correct answer.

Explanation

Multicast uses a group address so that a sender transmits one copy and the network replicates it only along branches leading to subscribed receivers, which conserves bandwidth. Unicast would require the sender to duplicate the stream per receiver, and broadcast reaches every host in the broadcast domain regardless of interest. Anycast delivers to a single nearest member rather than to all members of the group.

Question 28Network Fundamentals and Models

An engineer needs a Layer 3 device that forwards packets between two different subnets while blocking broadcast traffic from crossing between them. Which device role satisfies this requirement, and why?

  1. A router, because it forwards based on destination IP network and does not forward broadcasts by default Correct answer.
  2. A hub, because it repeats every frame to all attached segments
  3. A patch panel, because it physically separates the cabling of the two subnets
  4. A Layer 2 switch, because it maintains a MAC address table for both subnets

Explanation

A router terminates each Layer 2 broadcast domain and makes forwarding decisions from the destination IP address and routing table, so broadcasts are not propagated between interfaces by default. Switches and hubs operate within a single broadcast domain, so they cannot provide this boundary. This is why inter-subnet traffic requires a Layer 3 hop.

Question 29Network Fundamentals and Models

A host is configured with IP address 172.16.10.50 and mask 255.255.255.192. Which address is the directed broadcast address of the host's subnet?

  1. 172.16.10.64
  2. 172.16.10.255
  3. 172.16.10.63 Correct answer.
  4. 172.16.10.127

Explanation

The mask 255.255.255.192 is /26, so the subnet increment in the fourth octet is 64 and the host at .50 falls in the block from .0 to .63. The directed broadcast is the last address in that block, .63, with .0 as the network address and .1 through .62 usable for hosts.

Question 30Network Fundamentals and Models

A router receives a packet whose destination address matches two entries in its routing table: a static route to 10.20.0.0/16 and an OSPF-learned route to 10.20.5.0/24. Both have equal administrative distance preference in the sense that the static route is trusted more, yet the router forwards the packet toward the OSPF next hop. Which explanation is consistent with standard longest-prefix-match behavior?

  1. The static route was rejected because static routes cannot cover more than 256 subnets
  2. The router selects the more specific /24 prefix before considering administrative distance, because longest prefix match is evaluated first Correct answer.
  3. The router load-balances across both entries and the packet happened to leave via the OSPF path
  4. The OSPF route wins because routing protocols always override manually configured routes

Explanation

Cisco-style route selection applies longest prefix match before administrative distance, so a /24 learned by OSPF is preferred over a /16 static route for a destination inside 10.20.5.0/24. Administrative distance only breaks ties among routes to the same prefix learned from different sources. Load balancing occurs only among routes that are equal in prefix length and metric, which is not the case here.

Question 31Ethernet and Switching

A switch receives a frame with an unknown destination unicast MAC address. What is the default behavior of the switch?

  1. It sends the frame back out the ingress port only
  2. It queues the frame until the MAC address is learned
  3. It discards the frame and sends an ICMP unreachable message
  4. It floods the frame out all ports in the same VLAN except the ingress port Correct answer.

Explanation

When the destination MAC is not present in the MAC address table, the switch cannot identify a specific egress port. It floods the frame to every other port in the same VLAN (and to trunk ports carrying that VLAN) while never sending it back out the receiving port. This is the fundamental unknown-unicast flooding behavior of transparent bridging.

Question 32Ethernet and Switching

Which field of an Ethernet II frame allows the receiving NIC to determine where the payload ends and the Frame Check Sequence begins?

  1. The Length/Type field value of 0x0800
  2. The EtherType field Correct answer.
  3. The Start of Frame Delimiter
  4. The preamble

Explanation

In Ethernet II framing the two-byte field after the source MAC is the EtherType, which identifies the encapsulated protocol and defines the interpretation of the payload. The FCS is the final four bytes, so the receiver locates it by frame length and the EtherType context. The preamble and SFD are physical-layer synchronization patterns, not payload delimiters.

Question 33Ethernet and Switching

What is the primary purpose of Spanning Tree Protocol on a switched Layer 2 network?

  1. To load-balance traffic evenly across all redundant links
  2. To authenticate endpoints before they can send frames
  3. To prevent Layer 2 forwarding loops by blocking redundant paths Correct answer.
  4. To translate VLAN tags between different administrative domains

Explanation

Redundant links between switches create loops that cause broadcast storms and unstable MAC tables. STP elects a root bridge and places redundant ports into a blocking state so that a single active, loop-free topology exists. If a link fails, STP reconverges and unblocks an alternate path.

Question 34Ethernet and Switching

Which statement describes the difference between an access port and a trunk port on a switch?

  1. An access port can carry multiple VLANs, while a trunk port carries exactly one VLAN
  2. An access port carries a single VLAN untagged, while a trunk port carries multiple VLANs using tags Correct answer.
  3. An access port carries tagged frames, while a trunk port carries only untagged frames
  4. An access port is always a routed interface, while a trunk port is always a switched interface

Explanation

An access port belongs to one VLAN and normally sends frames untagged to end devices that are unaware of VLAN tagging. A trunk port carries traffic for multiple VLANs between switches or to VLAN-aware devices, using 802.1Q tags to identify each frame's VLAN. This distinction is fundamental to VLAN deployment design.

Question 35Ethernet and Switching

A frame arrives at a switch with a destination MAC address of FF:FF:FF:FF:FF:FF. How does the switch handle it?

  1. It forwards it only to the port learned for that address
  2. It sends it to the default gateway for resolution
  3. It floods it to all ports in the VLAN except the ingress port Correct answer.
  4. It drops it because broadcast addresses are not routable

Explanation

The all-ones address is the Layer 2 broadcast address, and switches always flood broadcast frames within the VLAN (excluding the ingress port). This is why broadcast domains are bounded by VLANs and routers. No MAC learning is associated with the broadcast address.

Question 36Ethernet and Switching

What does the 802.1Q tag add to an Ethernet frame?

  1. A 4-byte field inserted after the source MAC containing VLAN ID and priority Correct answer.
  2. A 2-byte field inserted before the preamble
  3. An 8-byte field replacing the EtherType
  4. A 6-byte field appended after the FCS

Explanation

802.1Q inserts a 4-byte tag between the source MAC address and the original EtherType. It contains the Tag Protocol Identifier (0x8100), a priority field, the DEI bit, and a 12-bit VLAN identifier. The frame's FCS is recalculated after tagging.

Question 37Ethernet and Switching

Which switching method begins forwarding a frame as soon as the destination MAC address has been read?

  1. Adaptive switching
  2. Store-and-forward switching
  3. Cut-through switching Correct answer.
  4. Fragment-free switching

Explanation

Cut-through switching reads only the first 6 bytes after the preamble to obtain the destination MAC and starts forwarding immediately. This minimizes latency but forwards frames with errors because the FCS has not yet been checked. Store-and-forward and fragment-free modes buffer more of the frame before forwarding.

Question 38Ethernet and Switching

Two switches are connected by a single link and both use default STP priorities. Which factor determines the root bridge?

  1. The switch with the highest port number on the link
  2. The switch that has been powered on the longest
  3. The switch with the lowest bridge ID, combining priority and MAC address Correct answer.
  4. The switch with the most active MAC address table entries

Explanation

The root bridge election compares bridge IDs, which consist of the 2-byte bridge priority followed by the 6-byte MAC address. The lowest value wins. With equal default priorities, the lower MAC address becomes the tiebreaker.

Question 39Ethernet and Switching

A switch port is configured with a static MAC address entry. What happens when a frame with that MAC as the source arrives on a different port?

  1. The switch keeps the static entry and does not relearn the address Correct answer.
  2. The switch converts the entry to a dynamic entry
  3. The switch disables the new port permanently
  4. The switch updates the entry to the new port automatically

Explanation

Static MAC entries are manually configured and are not overwritten by the learning process. Frames sourced from that MAC on another port will not move the entry, which can block legitimate traffic if the device is relocated. Administrators must remove or update the static entry manually.

Question 40Ethernet and Switching

An engineer needs to prevent a user from connecting an unauthorized switch that could inject BPDUs and alter the spanning tree topology. Which feature should be applied to the access port?

  1. BPDU guard Correct answer.
  2. Storm control
  3. MAC address notification
  4. Port mirroring

Explanation

BPDU guard places an edge port into an error-disabled state if it receives a BPDU, which indicates that a switch or other STP-speaking device has been attached. It is typically combined with PortFast on end-user ports. This protects the spanning tree topology from unauthorized devices.

Question 41Ethernet and Switching

A VLAN is configured on a switch, but no ports are assigned to it and no trunk carries it. What is the effect on traffic in that VLAN?

  1. The VLAN has no active member ports and carries no traffic Correct answer.
  2. The VLAN forwards traffic through the default VLAN
  3. The VLAN floods traffic to all trunk ports
  4. The VLAN automatically uses the management VLAN as a fallback

Explanation

A VLAN only carries traffic when at least one port is an active member (access or trunk). Without member ports, the VLAN exists in configuration but has no forwarding path. This is a common cause of connectivity failures after VLAN creation.

Question 42Ethernet and Switching

A network uses Rapid Spanning Tree Protocol. A root port fails on a non-root switch that has an alternate port. What is the expected convergence behavior?

  1. The alternate port transitions to forwarding after the standard 30-second listening and learning timers
  2. The network loops until an administrator clears the topology
  3. The alternate port transitions to forwarding almost immediately through precomputed roles Correct answer.
  4. The switch waits for the root bridge to send a new configuration BPDU before any change

Explanation

RSTP precomputes alternate and backup port roles so that a failed root port can be replaced by an alternate port without waiting for timer-based transitions. The proposal/agreement handshake allows rapid transition, typically in the range of a few seconds or less. This is the key advantage of RSTP over classic 802.1D.

Question 43Ethernet and Switching

Which statement about the native VLAN on an 802.1Q trunk is accurate?

  1. Native VLAN traffic is blocked by default on all trunks
  2. Native VLAN frames are always tagged with VLAN ID 1
  3. Native VLAN must be the highest VLAN ID on the trunk
  4. Native VLAN frames are sent untagged across the trunk Correct answer.

Explanation

802.1Q defines a single native VLAN per trunk whose frames are transmitted without a tag, preserving compatibility with devices that do not understand tagging. Best practice is to set the native VLAN to an unused VLAN and match it on both ends. A native VLAN mismatch can merge traffic between VLANs and cause inconsistencies.

Question 44Ethernet and Switching

A switch has learned MAC address 00:11:22:33:44:55 on port Gi0/1. A frame with this address as the destination arrives on Gi0/2. What does the switch do?

  1. It forwards the frame out Gi0/1 Correct answer.
  2. It updates the MAC table to point to Gi0/2
  3. It drops the frame because the destination is on another port
  4. It floods the frame out all ports including Gi0/2

Explanation

The destination MAC matches an existing table entry pointing to Gi0/1, so the switch forwards the frame only out that port. The ingress port Gi0/2 is irrelevant to the destination lookup. The table is updated only by source addresses, not destination addresses.

Question 45Ethernet and Switching

What is the purpose of the Forward Delay timer in classic IEEE 802.1D spanning tree?

  1. To age out dynamic MAC address entries
  2. To determine the maximum frame size on a trunk
  3. To control the time spent in listening and learning states before forwarding Correct answer.
  4. To set the interval between configuration BPDUs

Explanation

Forward Delay defines how long a port stays in the listening state and then the learning state before transitioning to forwarding. This delay allows the topology to stabilize and prevents temporary loops. The default value is 15 seconds for each state.

Question 46Ethernet and Switching

Which mechanism allows a single physical link between two switches to carry traffic for multiple VLANs while keeping broadcast domains separate?

  1. 802.1Q trunking Correct answer.
  2. Link aggregation with 802.3ad
  3. Port mirroring
  4. Jumbo frame support

Explanation

802.1Q trunking inserts a VLAN tag into each frame so that multiple VLANs can share one physical link while remaining logically separate broadcast domains. The receiving switch reads the tag and forwards the frame only within the indicated VLAN. Link aggregation increases bandwidth but does not separate broadcast domains by itself.

Question 47Ethernet and Switching

A host sends a frame to a destination MAC that is on the same VLAN but the switch's MAC table has no entry for it. Which two actions does the switch take? (Choose the best combined answer.)

  1. Flood the frame within the VLAN and learn the source MAC from the ingress port Correct answer.
  2. Send the frame only to the uplink trunk port
  3. Drop the frame and log an unknown unicast event
  4. Forward the frame to the default gateway and learn the destination

Explanation

For an unknown unicast destination, the switch floods the frame to all other ports in the VLAN. Simultaneously, it examines the source MAC and associates it with the ingress port, populating the MAC table. These two processes, flooding and learning, occur together on every frame.

Question 48Ethernet and Switching

An administrator observes that a trunk link between two switches is passing traffic for VLAN 10 but not VLAN 20, even though VLAN 20 exists on both switches. Which configuration issue is most likely?

  1. The trunk is using 802.1Q encapsulation
  2. VLAN 20 is not allowed on the trunk link Correct answer.
  3. The native VLAN is set to VLAN 1
  4. STP is disabled on the trunk

Explanation

Trunk ports maintain an allowed VLAN list, and a VLAN that is not in that list is not forwarded across the link. Even if the VLAN exists in the VLAN database on both switches, it must be permitted on the trunk. Checking the allowed list is the first troubleshooting step for this symptom.

Question 49Ethernet and Switching

What does the root guard feature do on a switch port?

  1. It limits the number of MAC addresses learned on the port
  2. It prevents the port from becoming a root port by discarding superior BPDUs Correct answer.
  3. It authenticates devices using 802.1X before allowing BPDUs
  4. It prevents the port from forwarding any user traffic

Explanation

Root guard enforces the placement of the root bridge by blocking ports that receive superior BPDUs. If a superior BPDU arrives, the port is placed in a root-inconsistent state and does not forward traffic until the condition clears. This prevents an unintended switch from taking over as root.

Question 50Ethernet and Switching

Which statement correctly describes the behavior of a switch when it receives a frame with a destination MAC address that is a multicast address?

  1. It drops the frame because multicast is not supported at Layer 2
  2. It forwards the frame to the router for replication
  3. It floods the frame to all ports in the VLAN unless multicast optimization is configured Correct answer.
  4. It forwards the frame only to ports that have joined the group via IGMP snooping

Explanation

By default, a switch treats multicast frames like broadcast and floods them to all ports in the VLAN. IGMP snooping can be enabled to constrain multicast forwarding to interested receivers. Without snooping, multicast traffic consumes bandwidth on every port.