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CCNA practice questions

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Question 1Network Fundamentals

A router forwards packets between different IP networks. At which OSI model layer does this forwarding decision primarily occur?

  1. Layer 1 – Physical
  2. Layer 2 – Data link
  3. Layer 4 – Transport
  4. Layer 3 – Network Correct answer.

Explanation

Routers choose an outbound interface by comparing the packet's destination logical address against a routing table, and logical addressing is defined at Layer 3. Layer 2 forwarding uses hardware addresses and stays inside a single broadcast domain. A Layer 3 switch performs the same lookup only when routing is enabled.

Question 2Network Fundamentals

Which protocol data unit (PDU) is created at the transport layer of the OSI model?

  1. Segment Correct answer.
  2. Frame
  3. Bit
  4. Packet

Explanation

The transport layer encapsulates application data into segments (TCP) or datagrams (UDP) and adds port numbers. Each lower layer renames the PDU as it adds its own header, so naming follows the layer that built it.

Question 3Network Fundamentals

How many bits long is a MAC address?

  1. 32 bits
  2. 128 bits
  3. 48 bits Correct answer.
  4. 64 bits

Explanation

MAC addresses are 48 bits, usually written as 12 hexadecimal digits. The first 24 bits identify the manufacturer (OUI) and the last 24 bits are assigned by that vendor. This size keeps addresses globally unique while fitting in a small frame header.

Question 4Network Fundamentals

Which TCP port is used by HTTPS by default?

  1. 443 Correct answer.
  2. 25
  3. 80
  4. 21

Explanation

HTTPS runs HTTP inside TLS and listens on TCP 443 by default, while plain HTTP uses TCP 80. Well-known ports below 1024 are assigned by IANA so clients know where to connect without being told.

Question 5Network Fundamentals

What is the maximum standard cable length for an Ethernet run over unshielded twisted-pair copper?

  1. 185 m
  2. 100 m Correct answer.
  3. 55 m
  4. 500 m

Explanation

Structured cabling standards limit a horizontal UTP channel to 100 m: up to 90 m of permanent cable plus 10 m of patch cords. Longer runs exceed the channel budget and cause signal attenuation and test failures.

Question 6Network Fundamentals

Which of these IPv4 addresses is a private address as defined by RFC 1918?

  1. 11.5.5.10
  2. 172.32.5.10
  3. 172.20.5.10 Correct answer.
  4. 192.169.5.10

Explanation

RFC 1918 reserves 10.0.0.0/8, 172.16.0.0/12 (172.16.0.0 through 172.31.255.255), and 192.168.0.0/16 for private use. Addresses in those ranges are not routed on the public Internet and normally require NAT to reach it.

Question 7Network Fundamentals

A host that cannot reach a DHCP server may assign itself an address from which range?

  1. 169.254.0.0/16 Correct answer.
  2. 10.0.0.0/8
  3. 192.168.0.0/16
  4. 127.0.0.0/8

Explanation

When DHCP fails, many operating systems fall back to link-local self-assignment using the 169.254.0.0/16 range, often called APIPA. The host verifies the address is unused with an ARP probe before using it. Such hosts can talk to other link-local hosts on the same segment but have no default gateway.

Question 8Network Fundamentals

What is the primary function of DNS?

  1. Map IP addresses to hardware addresses
  2. Encrypt traffic between clients and servers
  3. Resolve host names to IP addresses Correct answer.
  4. Assign IP addresses to hosts dynamically

Explanation

DNS is a distributed database that translates human-readable names, such as www.example.com, into the IP addresses that hosts actually use for delivery. Clients query a configured resolver, which walks or caches the hierarchy of name servers.

Question 9Network Fundamentals

A host must send a frame to another host on the same subnet but knows only the destination IPv4 address. How does it learn the destination MAC address?

  1. By sending an ARP request Correct answer.
  2. By sending a DNS query
  3. By sending a DHCP request
  4. By sending an ICMP echo request

Explanation

ARP broadcasts a request asking which device owns the target IPv4 address, and the owner replies unicast with its MAC address. The result is cached for a short time so later frames can be sent directly. This process only occurs for destinations the sender considers local.

Question 10Network Fundamentals

How many usable host addresses are available in a /27 IPv4 subnet?

  1. 14
  2. 32
  3. 62
  4. 30 Correct answer.

Explanation

A /27 borrows 27 network bits, leaving 5 host bits, so the subnet holds 2^5 = 32 addresses. Two of those are reserved for the network and broadcast addresses, leaving 30 assignable to hosts.

Question 11Network Fundamentals

What is the broadcast address of the subnet 172.16.4.64/26?

  1. 172.16.4.128
  2. 172.16.4.63
  3. 172.16.4.127 Correct answer.
  4. 172.16.4.191

Explanation

A /26 leaves 6 host bits, so each subnet contains 64 addresses and the subnets start at .0, .64, .128, and .192. The subnet beginning at .64 spans .64 through .127, making .127 the highest address and therefore the broadcast.

Question 12Network Fundamentals

A 24-port switch has a device connected to every port, and all ports are members of the same VLAN. How many collision domains exist?

  1. 2
  2. 12
  3. 1
  4. 24 Correct answer.

Explanation

Each switch port is its own collision domain because the switch buffers and forwards frames per port instead of repeating signals to all ports. All 24 ports remain in a single broadcast domain because they share one VLAN.

Question 13Network Fundamentals

Which IPv6 address type is automatically configured on an enabled interface and always begins with fe80::/10?

  1. Global unicast
  2. Multicast
  3. Link-local Correct answer.
  4. Unique local

Explanation

Every IPv6-enabled interface forms a link-local address from the fe80::/10 prefix, either from the MAC address or a randomized value. Link-local addresses are used for neighbor discovery and next-hop resolution and are never routed off the link.

Question 14Network Fundamentals

Which Ethernet frame field lets a receiving device detect a corrupted frame?

  1. Start frame delimiter
  2. Preamble
  3. Frame check sequence Correct answer.
  4. Type/length

Explanation

The frame check sequence is a CRC value calculated over the frame contents and placed in the trailer. The receiver recalculates the CRC and discards the frame if the values differ, which is why many corruption problems show up as dropped frames rather than errors at upper layers.

Question 15Network Fundamentals

Which set of flags describes the TCP three-way handshake in the order the packets are sent?

  1. ACK, SYN, ACK
  2. SYN, SYN-ACK, ACK Correct answer.
  3. SYN, ACK, SYN-ACK
  4. SYN, FIN, ACK

Explanation

The initiator sends a SYN with its initial sequence number, the responder replies with SYN and ACK acknowledging that number while offering its own, and the initiator finishes with an ACK. Both sides now have synchronized sequence numbers and can exchange data reliably.

Question 16Network Fundamentals

Which statement describes UDP?

  1. It performs a three-way handshake before data transfer
  2. It is connectionless and adds little overhead Correct answer.
  3. It guarantees in-order delivery of data
  4. It retransmits lost segments

Explanation

UDP sends datagrams without establishing a session, acknowledging receipt, or resequencing, so its header is only 8 bytes. Applications that prefer speed or handle recovery themselves, such as DNS, DHCP, and voice, use UDP.

Question 17Network Fundamentals

On a link where both endpoints are configured for full duplex, which function is not required?

  1. Preamble generation
  2. Framing
  3. CSMA/CD Correct answer.
  4. Error detection

Explanation

Full duplex uses separate transmit and receive wire pairs, so a station can send and receive simultaneously and collisions cannot occur. Collision detection and the associated backoff algorithm exist only for shared half-duplex media.

Question 18Network Fundamentals

Which group of channels in the 2.4 GHz band is non-overlapping?

  1. 1, 6, 11 Correct answer.
  2. 3, 8, 13
  3. 1, 5, 9
  4. 2, 7, 12

Explanation

2.4 GHz channels are spaced 5 MHz apart but each channel is about 22 MHz wide, so adjacent channels overlap. Choosing channels five apart, such as 1, 6, and 11, separates the center frequencies enough to avoid co-channel interference in the common regulatory domain.

Question 19Network Fundamentals

Which IEEE standard defines PoE that delivers up to about 15.4 W to a powered device?

  1. 802.3af Correct answer.
  2. 802.3at
  3. 802.3ad
  4. 802.11ac

Explanation

802.3af, commonly called PoE, provides roughly 15.4 W at the powered device over the same cable that carries data. 802.3at, or PoE+, raises that to about 25.5 W for devices such as access points and pan-tilt-zoom cameras.

Question 20Network Fundamentals

In which cloud service model does the provider manage the operating system, runtime, and middleware while the customer deploys only applications?

  1. PaaS Correct answer.
  2. On-premises
  3. SaaS
  4. IaaS

Explanation

Platform as a service supplies a managed runtime and supporting services so developers can push code without patching servers or installing middleware. In IaaS the customer still manages the guest OS, and in SaaS the customer simply consumes a finished application.

Question 21Network Fundamentals

An engineer must divide 192.168.10.0/24 into subnets that each support at least 25 hosts, using the longest prefix that still meets the requirement. Which prefix should be chosen?

  1. /27 Correct answer.
  2. /25
  3. /26
  4. /28

Explanation

A /27 leaves 5 host bits, giving 32 addresses and 30 usable hosts, which satisfies the 25-host requirement while creating 8 subnets. A /28 would yield only 14 usable hosts and therefore fail, so /27 is the longest prefix that still works.

Question 22Network Fundamentals

Which is a correctly compressed form of 2001:0db8:0000:0000:0000:0000:0000:0001?

  1. 2001:db8::1 Correct answer.
  2. 2001:db8::1::
  3. 2001:db8::1:0:0
  4. 2001:0db8:0:0:0:0:1

Explanation

Compression removes leading zeros in each group and replaces one contiguous run of all-zero groups with a double colon. Here that leaves 2001, db8, then the zero run, then 1, giving 2001:db8::1. The double colon may appear only once in an address.

Question 23Network Fundamentals

Which address is a valid host address on the subnet 10.1.1.0/30?

  1. 10.1.1.4
  2. 10.1.1.3
  3. 10.1.1.0
  4. 10.1.1.2 Correct answer.

Explanation

A /30 leaves 2 host bits, so the block covers four addresses: 10.1.1.0 through 10.1.1.3. The first address is the network ID and the last is the broadcast, leaving .1 and .2 as the only usable host addresses.

Question 24Network Fundamentals

A 255.255.255.224 mask is applied to 192.168.5.0. Which address belongs to the third subnet?

  1. 192.168.5.62
  2. 192.168.5.96
  3. 192.168.5.33
  4. 192.168.5.70 Correct answer.

Explanation

The mask 255.255.255.224 is a /27, so the block size is 32 and subnets begin at .0, .32, and .64. The third subnet spans 192.168.5.64 through 192.168.5.95, so .70 is a host inside it.

Question 25Network Fundamentals

Host A (192.168.1.10/24) sends a packet to 192.168.2.20 and uses default gateway 192.168.1.1. Which destination MAC address does the frame carry when it leaves Host A?

  1. The MAC address of 192.168.2.20
  2. The broadcast address FF:FF:FF:FF:FF:FF
  3. The MAC address of the default gateway Correct answer.
  4. The MAC address of Host A

Explanation

Host A compares the destination with its own mask, sees that 192.168.2.20 is on a different network, and forwards the frame to its default gateway. The frame's destination MAC is therefore the router interface's address, while the destination IP stays set to 192.168.2.20 for the whole trip.

Question 26Network Fundamentals

Which device primarily makes forwarding decisions based on destination MAC addresses?

  1. A firewall
  2. A Layer 2 switch Correct answer.
  3. A repeater hub
  4. A Layer 3 router

Explanation

A switch learns source MAC addresses and forwards frames based on the destination MAC address in its MAC address table. Routers forward using IP addresses, hubs simply repeat signals, and firewalls filter traffic by policy.

Question 27Network Fundamentals

What does a host use a default gateway for?

  1. To translate domain names into IP addresses
  2. To detect duplicate addresses on the link
  3. To assign an IP address automatically
  4. To forward traffic to another subnet Correct answer.

Explanation

A default gateway is a router interface on the host's local subnet. The host sends traffic destined for other subnets to that gateway for routing.

Question 28Network Fundamentals

What is the purpose of the TTL field in an IPv4 header?

  1. It specifies the priority for quality of service
  2. It identifies the upper-layer protocol being carried
  3. It limits how many hops a packet can traverse Correct answer.
  4. It verifies the integrity of the IP header

Explanation

Each router decrements the TTL by one, and a packet is discarded when the TTL reaches zero. This prevents packets from looping indefinitely through a network.

Question 29Network Fundamentals

Which connector is commonly used with twisted-pair Ethernet cabling?

  1. BNC
  2. RJ-45 Correct answer.
  3. SC
  4. LC

Explanation

Twisted-pair Ethernet cables typically terminate with RJ-45 connectors. LC and SC are fiber-optic connectors, and BNC is used with coaxial cable.

Question 30Network Fundamentals

A switch receives a frame with a destination MAC address that is not in its MAC address table. What does the switch do?

  1. It floods the frame out all other ports Correct answer.
  2. It sends the frame to the default gateway
  3. It drops the frame and logs an error
  4. It replies with an ICMP unreachable message

Explanation

When the destination MAC address is unknown, the switch floods the frame out every port except the ingress port. This behavior is called unknown unicast flooding.

Question 31Network Fundamentals

Which IPv6 address identifies the local loopback interface?

  1. fe80::1
  2. ::1 Correct answer.
  3. ff02::1
  4. ::

Explanation

The IPv6 loopback address is ::1, which is equivalent in purpose to 127.0.0.1 in IPv4. The address :: is unspecified, fe80::/10 is link-local, and ff02::1 is the all-nodes multicast address.

Question 32Network Fundamentals

Which sequence shows the DHCP messages used when a client obtains an IPv4 address lease?

  1. Offer, Discover, Request, Acknowledge
  2. Discover, Request, Offer, Acknowledge
  3. Discover, Offer, Request, Acknowledge Correct answer.
  4. Request, Offer, Discover, Acknowledge

Explanation

DHCP uses the DORA sequence: Discover, Offer, Request, and Acknowledge. The client discovers servers, receives an offer, requests the offer, and receives acknowledgment.

Question 33Network Fundamentals

Which TCP header field tells the sender how much data the receiver can accept?

  1. Window size Correct answer.
  2. Checksum
  3. Urgent pointer
  4. Sequence number

Explanation

The TCP window size field advertises the amount of data the receiver is currently willing to accept. This supports flow control between the endpoints.

Question 34Network Fundamentals

Which protocol typically uses UDP port 514 to forward log messages to a collector?

  1. NetFlow
  2. NTP
  3. Syslog Correct answer.
  4. SNMP

Explanation

Syslog commonly uses UDP port 514 to send event and log messages to a central collector. SNMP, NetFlow, and NTP use different ports for their respective functions.

Question 35Network Fundamentals

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

  1. To combine multiple links into one logical link
  2. To authenticate devices before they access the port
  3. To prevent Layer 2 forwarding loops Correct answer.
  4. To route packets between different VLANs

Explanation

Spanning Tree Protocol blocks redundant paths so that a Layer 2 topology remains loop-free. Without it, broadcast frames could circulate indefinitely and overwhelm the network.

Question 36Network Fundamentals

Which technology carries traffic for multiple VLANs over a single switch-to-switch link?

  1. VTP
  2. Port security
  3. EtherChannel
  4. 802.1Q tagging Correct answer.

Explanation

IEEE 802.1Q inserts a VLAN tag into Ethernet frames so that multiple VLANs can share a trunk link. The receiving switch reads the tag to determine the frame's VLAN membership.

Question 37Network Fundamentals

Which cloud characteristic lets a customer provision computing resources automatically without human interaction from the provider?

  1. High availability
  2. On-demand self-service Correct answer.
  3. Resource pooling
  4. Measured service

Explanation

On-demand self-service allows a customer to provision resources, such as virtual machines, through automation without requiring provider intervention. Resource pooling and measured service describe sharing and billing, not automatic provisioning.

Question 38Network Fundamentals

A host is configured with 192.168.10.130/26. What is the network address of its subnet?

  1. 192.168.10.128 Correct answer.
  2. 192.168.10.64
  3. 192.168.10.192
  4. 192.168.10.130

Explanation

A /26 mask has a block size of 64, producing subnets at .0, .64, .128, and .192. The address .130 falls within the .128 subnet, so its network address is 192.168.10.128.

Question 39Network Fundamentals

Which statement correctly distinguishes the control plane from the data plane in a router?

  1. The control plane builds routing information, while the data plane forwards packets. Correct answer.
  2. The control plane assigns MAC addresses, while the data plane resolves names.
  3. The control plane encrypts traffic, while the data plane authenticates users.
  4. The control plane forwards packets, while the data plane builds the routing table.

Explanation

The control plane runs routing protocols and builds the routing and forwarding tables. The data plane uses those tables to forward individual packets through the device.

Question 40Network Fundamentals

Two switches need more bandwidth and redundancy between them without STP blocking the extra links. Which solution should be used?

  1. Bundle the links into an EtherChannel Correct answer.
  2. Configure each link as an access port in a different VLAN
  3. Set all but one link to half duplex
  4. Enable BPDU guard on all connected ports

Explanation

An EtherChannel bundles parallel physical links into one logical link, and STP treats that bundle as a single path. All member links can then forward traffic while providing redundancy.

Question 41Network Access

Which statement describes a VLAN?

  1. A wireless client security profile.
  2. A physical cable segment connecting two hosts.
  3. A route between separate IP subnets.
  4. A logical broadcast domain on switches. Correct answer.

Explanation

A VLAN is a Layer 2 logical grouping that creates a separate broadcast domain on one or more switches. Devices in different VLANs require Layer 3 routing to communicate.

Question 42Network Access

Which switch port type carries traffic for one VLAN and typically connects to an end device?

  1. Access port Correct answer.
  2. Trunk port
  3. Routed port
  4. Tunnel port

Explanation

An access port is assigned to a single VLAN and normally connects to an end device such as a PC or printer. A trunk port carries traffic for multiple VLANs, usually between switches.

Question 43Network Access

On an 802.1Q trunk, frames in the native VLAN are sent in which form?

  1. Tagged with VLAN ID 1
  2. Double-tagged
  3. Tagged with a random VLAN ID
  4. Untagged Correct answer.

Explanation

802.1Q leaves native VLAN frames untagged, so both ends of the trunk must agree on the native VLAN. Tagged frames carry an explicit VLAN identifier.

Question 44Network Access

On a Cisco switch with default settings, which VLAN is assigned to all access ports?

  1. VLAN 1 Correct answer.
  2. VLAN 0
  3. VLAN 1005
  4. VLAN 10

Explanation

By default, all switch ports are access ports in VLAN 1. VLAN 1 is also the default native VLAN on trunk links.

Question 45Network Access

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

  1. To encrypt frames between switches.
  2. To assign IP addresses to VLAN interfaces.
  3. To prevent Layer 2 switching loops. Correct answer.
  4. To route packets between VLANs.

Explanation

STP prevents Layer 2 loops by blocking redundant paths while keeping a loop-free topology. Without STP, broadcast frames could circulate indefinitely.

Question 46Network Access

In STP, which switch is elected as the root bridge?

  1. The switch with the lowest bridge ID. Correct answer.
  2. The switch with the highest priority value.
  3. The switch with the most active ports.
  4. The switch with the highest MAC address.

Explanation

The bridge ID combines priority and MAC address, and the lowest value wins the root election. With equal priorities, the lowest MAC address decides.

Question 47Network Access

What does the Cisco PortFast feature do on an access port?

  1. It elects the port as the spanning-tree root port.
  2. It moves an access port directly to forwarding. Correct answer.
  3. It blocks all incoming frames from entering the port.
  4. It converts the access port into an 802.1Q trunk.

Explanation

PortFast skips the listening and learning stages on an edge port so it enters forwarding immediately. It should be enabled only on ports connected to end devices to avoid creating loops.

Question 48Network Access

Which protocol is a vendor-neutral neighbor discovery protocol defined by IEEE 802.1AB?

  1. LLDP Correct answer.
  2. Cisco VTP
  3. Cisco CDP
  4. Cisco DTP

Explanation

LLDP is the IEEE 802.1AB vendor-neutral neighbor discovery protocol. CDP is Cisco proprietary, while DTP and VTP serve other switching functions.

Question 49Network Access

How many bits does the 802.1Q tag use for the VLAN identifier?

  1. 16 bits
  2. 10 bits
  3. 12 bits Correct answer.
  4. 8 bits

Explanation

The 802.1Q tag includes a 12-bit VLAN identifier, allowing VLAN IDs 0 through 4095, with 1 through 4094 usable. The tag also carries priority and other fields.

Question 50Network Access

Which command limits an 802.1Q trunk to carry only VLANs 10 and 20?

  1. switchport trunk allowed vlan 10,20 Correct answer.
  2. switchport access vlan 10,20
  3. switchport trunk native vlan 10,20
  4. switchport mode trunk vlan 10,20

Explanation

The switchport trunk allowed vlan command defines which VLANs may traverse a trunk. The native VLAN command sets only the untagged VLAN and does not create an allowed list.