CCNA Devnet Network Fundamentals Questions

In SDN, the southbound API is the interface between the controller and the network devices (switches, routers). It allows the controller to install forwarding rules, such as flow entries in OpenFlow switches, enabling centralized control of the data plane.

TCP (Transmission Control Protocol) is the correct choice because it provides reliable, ordered delivery of data with error checking. Its key characteristic is the 3-way handshake (SYN, SYN-ACK, ACK) used to establish a connection before data transfer, ensuring both endpoints are synchronized and ready for reliable communication.

With a /25 mask (255.255.255.128), the network is divided into two subnets: 192.168.1.0-127 and 192.168.1.128-255. The two hosts are in different subnets and require a router to communicate.

The client sends a SYN segment to start the handshake.

ARP (Address Resolution Protocol) is used to map an IP address to a MAC address on a local network.

Layer 3 (Network layer) handles IP addressing and routing decisions.

DNS and DHCP use UDP because they are lightweight and can tolerate some loss. HTTP uses TCP, and SMTP uses TCP.

The TCP three-way handshake consists of SYN, SYN-ACK, ACK.

TCP is connection-oriented and provides reliability.

In the 2.4 GHz band, channels 1, 6, and 11 are the only non-overlapping channels when using 20 MHz channel spacing, as each channel occupies 22 MHz of bandwidth and these three are spaced 25 MHz apart. Channels 1 and 6 are correct because they do not overlap, minimizing co-channel interference and maximizing throughput.

NETCONF uses XML and is used for configuration management, while OpenFlow pushes flow entries to switches.

The AAAA record is used for IPv6 address mapping.

OpenFlow and NETCONF are southbound protocols used between controller and network devices.

Switches operate at Layer 2 and forward frames based on MAC addresses within a LAN.

802.11ax, marketed as Wi-Fi 6, is the correct answer because it is the only standard among the options that operates in both the 2.4 GHz and 5 GHz bands and introduces OFDMA, 1024-QAM, and improved MU-MIMO for higher efficiency and throughput. Wi-Fi 6 is backward compatible with previous standards but requires compatible clients to leverage its full capabilities.

TXT records store arbitrary text, commonly used for SPF, DKIM, and domain verification.

A /25 subnet has 7 bits for hosts (32-25=7), giving 2^7 = 128 total addresses, minus 2 (network and broadcast) = 126 usable hosts.

HTTP/2 is binary, supports multiplexed streams, and uses HPACK for header compression.

HTTPS uses TLS for encryption, involves certificate verification, and negotiates a symmetric session key. It does not use UDP typically (TCP is used) and it is not stateless after the handshake.

HTTP/2 introduces multiplexed streams, allowing multiple requests/responses in parallel over a single connection.

HTTP/2 is binary, multiplexes streams, and uses HPACK for header compression.

Option A is correct because RFC 1918 reserves the 192.168.0.0/16 block (192.168.0.0 – 192.168.255.255) as a private IPv4 address range, meaning these addresses are not routable on the public internet and are intended for use within private networks.

The southbound API (e.g., OpenFlow, NETCONF) is used to communicate between the SDN controller and the data plane devices.

UDP is connectionless and has lower overhead, but is unreliable.

Option C (255.255.255.224, /27) provides 5 host bits, yielding 2^5 = 32 total addresses per subnet. Subtracting the network and broadcast addresses leaves exactly 30 usable hosts, meeting the requirement precisely.

A /26 mask provides 62 usable hosts (2^(32-26)-2=62), which is the smallest subnet that supports 50 hosts.

Switches operate at Layer 2 (Data Link layer) because they use MAC addresses to forward frames.

The TCP three-way handshake begins with the client sending a SYN segment to initiate a connection. In the second step, the server responds with a SYN-ACK segment, which both acknowledges the client's SYN (using the ACK flag) and synchronizes its own sequence number (using the SYN flag). This combined flag is essential for establishing a reliable, bidirectional connection.

A CNAME record creates an alias that points to the canonical name. The A record points to an IP address, not another domain.

HTTPS uses TLS (Transport Layer Security) to encrypt HTTP traffic and verify server identity.

TCP (Transmission Control Protocol) is correct for reliable data transfer because it provides connection-oriented communication with sequencing, acknowledgments, and retransmission of lost packets, ensuring data arrives intact and in order. This makes it ideal for microservices that need guaranteed delivery, such as database transactions or order processing.

The private IPv4 ranges are 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16. 169.254.0.0/16 is link-local (APIPA).

UDP is a connectionless transport layer protocol that provides minimal overhead, making it ideal for applications like DNS and DHCP that require fast, lightweight communication. DNS uses UDP for queries (port 53) and DHCP uses UDP for client-server exchanges (ports 67/68) because they can tolerate occasional packet loss and benefit from the reduced latency.

Layer 2 (Data Link) uses MAC addresses for local delivery.

Channels 1, 6, and 11 are the only non-overlapping channels in 2.4 GHz.

/24 means subnet mask 255.255.255.0. Network address is 192.168.1.0, broadcast is 192.168.1.255. Usable hosts range from .1 to .254.

The control plane (decides traffic flow) and data plane (forwards traffic) are the two key planes in SDN, with the controller centralizing the control plane.

To support at least 50 hosts, you need 6 host bits (2^6 - 2 = 62 usable addresses). A /26 subnet mask (255.255.255.192) provides exactly 6 host bits, meeting the requirement. The original /24 network is borrowed with 2 subnet bits, yielding 4 subnets of 64 addresses each.

Southbound API is used by the SDN controller to communicate with network devices (e.g., switches, routers) to enforce forwarding rules.

The Session layer (Layer 5) manages sessions between applications. The Transport layer handles end-to-end communication.

The Network layer (Layer 3) is responsible for packet forwarding and routing, using logical IP addresses to determine the best path from source to destination. Protocols like IP (IPv4/IPv6) and routing protocols (e.g., OSPF, BGP) operate at this layer to make forwarding decisions. The traceroute command is a common tool that leverages Layer 3 TTL (Time-to-Live) fields to map the path packets take.

UDP (User Datagram Protocol) is a connectionless transport-layer protocol that does not require a handshake (no SYN/SYN-ACK/ACK) and has minimal header overhead (only 8 bytes, compared to TCP's 20 bytes). This makes it ideal for applications like DNS queries, streaming media, or real-time communications where low latency is more critical than guaranteed delivery.

Multiplexing is the HTTP/2 feature that allows multiple concurrent streams to share a single TCP connection. This eliminates head-of-line blocking at the application layer by enabling the interleaving of frames from different streams, so a slow response on one stream does not block others.

NETCONF is a network management protocol used to install, manipulate, and delete the configuration of network devices. In the SDN architecture, the southbound interface is the layer that connects the control plane to the data plane, and NETCONF operates as a southbound protocol by carrying configuration data from a controller or management system down to network devices.

The Network layer (Layer 3) is responsible for logical addressing and routing packets between different networks. Protocols like IP (IPv4/IPv6) use routing tables and algorithms (e.g., OSPF, BGP) to determine the best path for forwarding packets across multiple hops. Without Layer 3, traffic could not leave a local broadcast domain.

Option C (10.0.0.0/8) is correct because RFC 1918 reserves this range, along with 172.16.0.0/12 and 192.168.0.0/16, for private IPv4 addressing. These addresses are not routable on the public internet and are intended for use within private networks, such as corporate LANs or home networks.

WPA3 is the latest standard with stronger encryption (SAE) and is recommended for modern networks.

The A record maps a hostname to an IPv4 address, the AAAA record maps a hostname to an IPv6 address, and the CNAME record maps an alias hostname to the canonical (true) hostname. These three are the most common DNS record types used for hostname-to-IP or alias resolution in both IPv4 and IPv6 networks.

HTTP/2 multiplexing allows multiple streams to be sent concurrently over a single TCP connection, reducing head-of-line blocking.

Private IPv4 ranges: 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16.

TCP is a connection-oriented protocol that provides reliable, ordered delivery and uses a three-way handshake (SYN, SYN-ACK, ACK) to establish a connection.

The Authorization header is the standard HTTP header used to transmit credentials (such as Basic, Bearer, or Digest tokens) to authenticate a REST API client. RFC 7235 defines this header as the mechanism for carrying authentication information from the client to the server, making it the correct choice for passing credentials in the HTTP header.

Option A is correct because Wi-Fi 6 (802.11ax) introduces Orthogonal Frequency Division Multiple Access (OFDMA), which subdivides a channel into smaller resource units (RUs) to serve multiple clients simultaneously, significantly improving efficiency in dense environments compared to Wi-Fi 5's OFDM that allocates the entire channel to a single user per transmission.

TCP provides reliability, ordered delivery, and connection-oriented communication.

TCP provides reliability, ordering, flow control, and retransmission. It uses a three-way handshake to establish a connection.

RFC 1918 defines 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16.

AAAA records map hostnames to IPv6 addresses.

Option B is correct because SDN separates the control plane from the data plane, allowing network administrators to automate configuration changes through a centralized controller (e.g., OpenFlow or Cisco APIC-EM). This eliminates the need for manual, device-by-device CLI changes, reducing human error and enabling rapid, consistent updates across the entire network.

HTTP 404 indicates the requested resource could not be found on the server.

In the 2.4 GHz ISM band, channels 1, 6, and 11 are the only three non-overlapping channels, each separated by 25 MHz, which prevents co-channel interference. This configuration maximizes throughput and minimizes interference from neighboring networks, making it ideal for high-density environments like hospitals.

MAC addresses operate at Layer 2 (Data Link) of the OSI model because they are used for local network addressing and frame delivery between directly connected devices. The Data Link layer encapsulates packets into frames and uses MAC addresses to identify source and destination interfaces on the same network segment, as defined by IEEE 802 standards.

Channels 1, 6, and 11 are the only non-overlapping channels in the 2.4 GHz band.

Option B is correct because a /25 prefix length corresponds to a subnet mask of 255.255.255.128, which provides 2^(32-25) - 2 = 128 - 2 = 126 usable host addresses. The network address is 172.16.5.0, and the broadcast address is 172.16.5.127, leaving addresses 172.16.5.1 through 172.16.5.126 for hosts.

Option A is correct because the server must present a valid digital certificate during the TLS handshake to prove its identity to the client. This certificate contains the server's public key and is signed by a trusted Certificate Authority (CA), enabling the client to verify the server's authenticity before proceeding with encrypted communication.

Option A is correct because UDP does not require a three-way handshake (SYN, SYN-ACK, ACK) before data transmission, eliminating the connection setup latency inherent in TCP. This makes UDP ideal for real-time applications like VoIP or video streaming where low delay is critical.

VLANs operate at Layer 2 (Data Link) by tagging frames with VLAN IDs to separate broadcast domains.

UDP is a connectionless transport protocol, meaning it does not establish a dedicated end-to-end connection before sending data. This characteristic allows for low-latency, best-effort delivery without the overhead of connection setup, which is ideal for applications like DNS queries or streaming media where speed is prioritized over reliability.

5 GHz offers more non-overlapping channels and less interference from common devices like microwaves and Bluetooth.

TCP provides a three-way handshake, sequence numbering for ordering, and flow control.

UDP is a connectionless transport protocol that does not provide retransmission of lost packets. In VoIP, packet loss directly degrades call quality because lost audio data is never resent, leading to gaps or distortion in the conversation.

802.11ax (Wi-Fi 6) supports both 2.4 GHz and 5 GHz bands, offering improved efficiency.

In SDN architecture, the control plane is responsible for making forwarding decisions by maintaining the network topology and computing paths for traffic flows. It communicates these decisions to the data plane via southbound protocols like OpenFlow or NETCONF, ensuring that packets are forwarded according to the desired policies.

VLANs operate at Layer 2 (Data Link) because they segment broadcast domains based on MAC addresses and logical grouping, but they do not involve IP routing (Layer 3).