CCNA Network Fundamentals Questions

The certificate proves the server's identity.

UDP is connectionless, so it skips the TCP three-way handshake before transmitting. Real-time applications such as voice and video avoid that setup delay, reducing latency and satisfying the stem's requirement for timely delivery over reliability.

The show ip access-lists command displays the configured ACLs and their entries, including match counters if the ACL has been applied and is counting matches. By examining the ACL entries, the engineer can see if there is a deny statement that would block traffic from the client to the web server. The match counters can also indicate if packets are hitting a particular entry, which helps confirm if the ACL is the cause of the problem.

VLAN tags are carried in the Ethernet frame header, so segmentation of a broadcast domain occurs at Layer 2, the Data Link layer. Layer 3 handles logical IP addressing and routing between VLANs, not the broadcast domain boundary itself.

UDP operates without establishing a session before transmission, so no handshake, sequencing or acknowledgement occurs between endpoints. This connectionless behaviour directly satisfies the stem's constraint: an application using UDP sends datagrams independently, with no prior path negotiation or state maintained between sender and receiver.

The 5 GHz band offers more non-overlapping channels and avoids congestion from microwave ovens, Bluetooth, and cordless phones that crowd 2.4 GHz. This directly maximises performance and minimises interference as the scenario requires, though at the cost of shorter range.

TCP's sliding window mechanism lets the receiver advertise how much data it can buffer, so a fast sender cannot overwhelm a slower receiver. This directly satisfies the high-reliability requirement in the stem by preventing buffer overflow and packet loss during transmission.

The requests library inspects the Content-Encoding header and transparently decompresses gzip (and deflate) bodies when you use response.text or response.json(). This allows the developer to parse the JSON payload without manual intervention. The raw compressed bytes are only visible via response.content, so using the higher-level accessors triggers the automatic decompression needed for this scenario.

UDP provides no retransmission mechanism, so datagrams dropped in transit are never recovered, producing gaps that degrade VoIP audio. TCP would retransmit lost segments, but UDP's fire-and-forget design leaves loss concealment entirely to the application codec.

In NETCONF, the `<get-config>` RPC requires a `<source>` element that identifies the configuration datastore to retrieve. The `<running/>` element inside `<source>` specifies the running configuration. This is defined in RFC 6241 and is mandatory for `<get-config>`. Without it, the server cannot determine which datastore to query. The engineer must include this exact structure to retrieve the running config successfully.

Internal names like inventory.corp.local are only authoritative on the corporate DNS infrastructure, which a public resolver such as 8.8.8.8 cannot see. Replacing the nameserver with the internal resolver lets the workstation query the zone that actually holds those records, and the search domain allows short names to be expanded automatically.

An A record maps a domain name to an IPv4 address. When an application needs to resolve a hostname to an IPv4 address, it queries for the A record. This is the standard and correct record type for IPv4 address resolution. The scenario specifically asks for an IPv4 address, so the A record is the right choice.

Delayed acknowledgment is a TCP optimization where the receiver waits for a short period or until it has received multiple segments before sending an ACK. This reduces the number of ACK packets and improves network efficiency. The scenario describes the server waiting and then sending a single acknowledgment for multiple segments, which is exactly how delayed ACK works. It is commonly used to reduce overhead, especially for interactive traffic.

The Label Switch Router (LSR) is a core MPLS device that forwards packets based on labels. It examines the incoming label, looks up the next-hop in its Label Forwarding Information Base (LFIB), swaps the label, and forwards the packet. This label-based forwarding is faster and more efficient than traditional IP routing lookups.

802.11ax, marketed as Wi-Fi 6, operates in both the 2.4 GHz and 5 GHz bands, satisfying the dual-band requirement in the stem. Unlike 802.11ac, which is 5 GHz only, 802.11ax supports concurrent dual-band operation, delivering higher throughput and improved efficiency in dense environments.

The control plane holds the centralised logic that computes forwarding decisions, programming them down to the data plane via southbound APIs. The data plane merely executes those instructions, which is the SDN separation of concerns.

VLAN tags and 802.1Q trunk encapsulation are defined in Ethernet frames, so VLANs operate at Layer 2 of the OSI model. This satisfies the stem's requirement to identify the layer governing inter-VLAN connectivity across the trunked switch.

TXT records carry arbitrary text, which SPF publishes as a v=spf1 string listing authorised sending hosts. Domain owners add this record so receivers can verify mail legitimacy, satisfying the stem's ownership-verification requirement for email security.

802.11ac operates in the 5 GHz band, which offers wider channels and less interference than 2.4 GHz, enabling the higher throughput and modulation rates the standard specifies. The 2.4 GHz band is handled by 802.11b/g/n instead.

TCP provides connection-oriented, reliable delivery through sequence numbers, acknowledgements and retransmission of lost segments, which HTTP requires. UDP, by contrast, is connectionless and offers no delivery guarantee. This satisfies the stem's requirement for a transport layer protocol guaranteeing reliable delivery for HTTP traffic.

AAAA records map a hostname to a 128-bit IPv6 address, the direct counterpart to A records for IPv4. Resolvers query AAAA when the client requests IPv6, so it satisfies the requirement to resolve a domain name to an IPv6 address.

POST submits a payload to the collection endpoint, creating a new resource, and the JSON body travels in the request. GET, PUT and DELETE cannot create a resource this way, so POST matches the API's create requirement.

HTTP persistent connections, also known as keep-alive, allow multiple HTTP requests and responses to be sent over a single TCP connection. This avoids the overhead of establishing a new TCP handshake for each request, reducing latency and improving performance for applications that make frequent API calls to the same server.

192.168.10.1 is a valid host address within the 192.168.10.0/24 subnet. It is commonly used as the default gateway or management address on network devices. Since it is not the network address or the broadcast address, it can be assigned to the switch's management interface and reached from other hosts on the same subnet.

A switch operates at Layer 2 and forwards frames based on destination MAC addresses. Within a VLAN, it maintains a MAC address table and forwards frames only to the port where the destination MAC is known, thereby enabling communication between devices in the same VLAN while isolating traffic from other VLANs.

HPACK is the header compression scheme defined specifically for HTTP/2, encoding header fields into a compact indexed format and eliminating redundant transfers across streams. This directly satisfies the stem's requirement to reduce overhead by compressing headers, unlike HTTP/1.1's uncompressed plaintext headers.

UDP omits handshaking, acknowledgements and retransmission, so lost packets are not resent and latency stays low. That satisfies the streaming constraint of minimising delay at the cost of occasional loss, which TCP's reliability mechanisms would worsen.

The southbound API sits below the controller, translating its forwarding decisions into device-level configuration. OpenFlow is the canonical example, programming match-action flow tables on switches. This satisfies the stem's requirement for the interface used to configure forwarding behaviour on network devices.

A CNAME record points the queried name at a canonical name rather than an address, so resolution continues against that target. The queried domain therefore acts purely as an alias, holding no A or AAAA record of its own.

A /26 mask yields 64 addresses, leaving 62 usable hosts after reserving network and broadcast addresses, which satisfies the 50-host requirement with minimal waste. A /27 would provide only 30 usable hosts, insufficient here, while a /25 wastes 126 addresses.

Netcat with the verbose and zero-I/O scan flags opens a TCP connection to the specified host and port, reporting whether the three-way handshake succeeds. This directly answers the question of whether the API's listening port is reachable from the client, which is exactly the precondition the Python script depends on.

HPACK reduces header overhead.

MAC addresses are used at Layer 2 for local network communication.

Multiplexing in HTTP/2 allows multiple request and response messages to be interleaved on a single TCP connection. Each stream is independent, and responses can be received out of order. This eliminates head-of-line blocking at the HTTP level and improves performance by allowing parallel transfers without opening multiple connections.

TXT records hold arbitrary text and carry the SPF policy string and DKIM public key, letting receivers verify sending authorisation and message signatures. No other record type accommodates these free-form verification values at the domain level.

AAAA records map a hostname to an IPv6 address, exactly matching the requirement to resolve 'payment-service.example.com' to its IPv6 address. The A record serves the same purpose for IPv4 only, so it cannot satisfy the IPv6 constraint.

DHCP relies on UDP because clients broadcast discovery packets before obtaining an IP address, so no unicast session exists. UDP's connectionless, low-overhead delivery on ports 67/68 lets the four-step DORA exchange complete without TCP handshake delays, satisfying the requirement to identify applications that commonly use UDP.

NETCONF over SSH encrypts the session and exposes configuration as structured XML, so the script can retrieve the running datastore with <get-config> and parse it reliably. It avoids parsing CLI text and matches the requirement for programmatic, structured retrieval over an encrypted transport, which is exactly what the scenario demands for automated comparison.

In the 2.4 GHz band, only channels 1, 6 and 11 are conventionally non-overlapping, each separated by five 5 MHz steps so their 22 MHz-wide signals do not overlap. Channel 6 sits between 1 and 11, satisfying the stem's non-overlapping requirement.

VLAN tagging inserts 802.1Q tags into Ethernet frames, which are Layer 2 constructs. The switch examines these tags to segregate broadcast domains, so VLAN membership is determined at the Data Link layer rather than Layer 3.

When a host determines that the destination IP is not on its local subnet, it forwards the packet to the default gateway. The gateway then routes the packet toward the destination. This is the primary function of a default gateway in IP networking.

PUT is idempotent: repeating the same request yields the same resource state. It replaces the target resource entirely with the enclosed representation, unlike PATCH, which applies partial modifications, or POST, which is neither idempotent nor a full replacement.

UDP is a best-effort transport with no acknowledgments or retransmission timers. For thousands of sensors sending frequent small readings where the design explicitly tolerates loss, this fire-and-forget behavior eliminates the overhead and latency that TCP's reliability mechanisms would add, which matches the stated priorities.

A /26 mask leaves 6 host bits, yielding 62 usable addresses after reserving network and broadcast, which satisfies the 50-host minimum. Smaller masks such as /25 waste 64 addresses unnecessarily, while /27 provides only 30 usable hosts and fails the requirement.

Southbound APIs sit between the controller and the forwarding plane, carrying instructions such as OpenFlow flow-mod messages that program device forwarding tables. Northbound APIs instead expose controller capabilities upward to applications, so only the southbound interface satisfies the stem's requirement to reach network devices directly.

Borrowing three host bits gives 2^3 = 8 subnets, satisfying the five-subnet requirement, with mask 255.255.255.224. Each subnet then has 2^5 - 2 = 30 usable host addresses after reserving the network and broadcast addresses.

In the TCP three-way handshake, the server's SYN-ACK segment acknowledges the client's SYN by setting the acknowledgment number to the client's initial sequence number (ISN) plus one. The plus-one accounts for the SYN flag consuming one sequence number. This field is what tells the client that the server received the SYN and expects the next byte from the client to be that value, completing the second step of the handshake.

The Authorization header is used to carry credentials for authenticating the client with the server. For token-based authentication, the token is typically included as 'Bearer <token>'. This is the standard way to send authentication information in HTTP requests, and it is expected by most REST APIs.

GET is the correct HTTP method for retrieving data without side effects. In RESTCONF, the /restconf/data path accesses the datastore, and the module-qualified name ietf-interfaces:interfaces identifies the YANG container. A GET returns the configured and operational state of interfaces, matching the requirement to read statistics without altering configuration.

Cisco DNA Center uses a custom header X-Auth-Token to carry the authentication token obtained from the /dna/system/api/v1/auth/token endpoint. After a successful login, the response includes a Token field, which must be placed in the X-Auth-Token header for subsequent API calls. This is the correct way to authenticate to DNA Center's REST API.