CSLB General Building (B) — All Questions

Which layer of the OSI model is responsible for logical addressing and determining the best path for packets across an internetwork?

• a.Layer 2 (Data Link)
• b.Layer 1 (Physical)
• c.Layer 3 (Network)✓
• d.Layer 4 (Transport)

Layer 3, the Network layer, handles logical addressing such as IP and makes routing decisions to move packets between networks. The Data Link layer uses physical MAC addresses for local delivery, while the Transport layer manages end-to-end segmentation. Routers operate primarily at Layer 3.

A network administrator needs to identify the protocol data unit (PDU) used at the Transport layer of the OSI model. Which term applies?

• a.Frame
• b.Segment✓
• c.Packet
• d.Bit

At the Transport layer the PDU is called a segment (or datagram for UDP). Packets exist at the Network layer, frames at the Data Link layer, and bits at the Physical layer. Knowing PDU names per layer helps when interpreting protocol behavior.

Which protocol and port number are used by HTTPS for secure web traffic by default?

• a.TCP 443✓
• b.TCP 80
• c.UDP 53
• d.TCP 22

HTTPS uses TCP port 443 and secures web traffic with TLS. Port 80 is plain HTTP, port 53 is DNS, and port 22 is SSH. Memorizing well-known ports is essential for firewall and troubleshooting work.

What is the default port used by the Domain Name System (DNS) for standard name resolution queries?

• a.TCP 25
• b.TCP 110
• c.UDP 67
• d.UDP 53✓

DNS uses UDP port 53 for most standard queries because they are small and benefit from low overhead. TCP 53 is used for zone transfers and larger responses. Ports 25, 110, and 67 belong to SMTP, POP3, and DHCP respectively.

An engineer must choose an address class for a private network that supports up to 500 hosts on a single subnet. Which private range is most appropriate to draw from?

• a.169.254.0.0/16
• b.10.0.0.0/8✓
• c.224.0.0.0/4
• d.127.0.0.0/8

The 10.0.0.0/8 range is an RFC 1918 private block that easily provides subnets large enough for 500 hosts. 169.254.0.0/16 is APIPA link-local, 224.0.0.0/4 is multicast, and 127.0.0.0/8 is loopback. Private ranges avoid public IP consumption.

How many usable host addresses are available in a subnet with a /29 prefix?

• a.2
• b.4
• c.6✓
• d.8

A /29 leaves 3 host bits, giving 2^3 = 8 total addresses, minus the network and broadcast addresses, for 6 usable hosts. Subnetting math requires subtracting two reserved addresses from the total. /29 subnets are common for small point-to-point or device segments.

Which IPv6 address type begins with the prefix FE80::/10 and is used only for communication on the local link?

• a.Link-local✓
• b.Global unicast
• c.Anycast
• d.Multicast

Link-local IPv6 addresses use the FE80::/10 prefix and are auto-configured on every interface for local-link communication. Global unicast addresses are routable on the internet, while multicast uses FF00::/8. Link-local addresses are never routed beyond the local segment.

A star topology relies on which central device to interconnect all end nodes?

• a.A repeater between each pair of nodes
• b.A central switch or hub✓
• c.A shared coaxial bus
• d.A ring of daisy-chained cables

In a star topology every node connects to a central switch or hub, which forwards traffic between them. A failure of one cable affects only that node, improving fault isolation. Bus and ring topologies use shared media that create single points of failure.

Which cabling standard defines the maximum supported distance of 100 meters for a twisted-pair Ethernet run?

• a.1000BASE-LX
• b.10GBASE-ER
• c.100BASE-FX
• d.1000BASE-T✓

1000BASE-T runs over twisted-pair copper and is limited to 100 meters per segment. The other options are fiber standards that support much longer distances. The 100-meter copper limit includes patch cords and horizontal cabling.

What is the primary purpose of a VLAN in a switched network?

• a.To logically segment a physical switch into separate broadcast domains✓
• b.To increase the speed of individual switch ports
• c.To convert Layer 2 frames into Layer 3 packets
• d.To provide power to connected devices

A VLAN logically segments a switch so that ports belong to separate broadcast domains without needing additional physical switches. This improves security and reduces broadcast traffic. Routing between VLANs still requires a Layer 3 device.

Which protocol resolves an IPv4 address to a MAC address on a local Ethernet segment?

• a.DNS
• b.ICMP
• c.ARP✓
• d.NTP

ARP (Address Resolution Protocol) maps a known IPv4 address to the MAC address needed for Layer 2 delivery. DNS resolves names to IPs, ICMP handles diagnostics, and NTP synchronizes time. ARP operates only within a local broadcast domain.

A company wants clients to obtain IP configuration automatically. Which protocol assigns addresses, subnet masks, gateways, and DNS servers dynamically?

• a.DNS
• b.DHCP✓
• c.SNMP
• d.LDAP

DHCP dynamically leases IP addresses along with subnet mask, default gateway, and DNS server information to clients. This eliminates manual configuration and reduces addressing errors. DHCP uses UDP ports 67 and 68 for server and client communication.

In the TCP three-way handshake, which sequence of flags correctly establishes a connection?

• a.ACK, SYN-ACK, SYN
• b.FIN, ACK, RST
• c.PSH, URG, ACK
• d.SYN, SYN-ACK, ACK✓

The TCP three-way handshake proceeds as SYN, then SYN-ACK, then ACK to establish a reliable session. FIN and RST relate to closing or resetting connections. Understanding the handshake helps diagnose connection setup failures.

Which cloud service model provides virtual machines, storage, and networking that customers manage themselves?

• a.IaaS✓
• b.SaaS
• c.PaaS
• d.DaaS

Infrastructure as a Service (IaaS) delivers fundamental compute, storage, and network resources that the customer configures and manages. SaaS delivers finished applications, and PaaS provides a development platform. IaaS offers the most customer control among cloud models.

What distinguishes UDP from TCP at the Transport layer?

• a.UDP guarantees ordered delivery through sequencing
• b.UDP performs a three-way handshake before sending data
• c.UDP is connectionless and does not guarantee delivery✓
• d.UDP always encrypts application data

UDP is connectionless, has low overhead, and does not guarantee delivery, ordering, or retransmission. This makes it ideal for latency-sensitive traffic such as VoIP and streaming. TCP, by contrast, is connection-oriented and reliable.

A /24 network needs to be divided into four equal subnets. Which new prefix length should be used?

• a./25
• b./26✓
• c./27
• d./28

Borrowing two host bits from a /24 creates four subnets, resulting in a /26 prefix. Each /26 subnet provides 62 usable hosts. The formula 2^n subnets requires n borrowed bits, so 2^2 equals four subnets.

Which network device forwards frames based on MAC address tables and operates primarily at Layer 2?

• a.Router
• b.Firewall
• c.Load balancer
• d.Switch✓

A switch builds a MAC address table and forwards frames only to the port associated with the destination MAC, operating at Layer 2. Routers work at Layer 3 using IP addresses. Switching reduces collisions by creating dedicated collision domains per port.

Which IEEE standard defines VLAN tagging on Ethernet trunk links?

• a.802.1Q✓
• b.802.3af
• c.802.11ac
• d.802.1X

IEEE 802.1Q defines the frame tagging method used to carry multiple VLANs across a trunk link. 802.3af covers PoE, 802.11ac is Wi-Fi, and 802.1X is port-based access control. The 802.1Q tag adds a 4-byte field to the Ethernet frame.

What is the purpose of a default gateway on a host's IP configuration?

• a.To resolve domain names into IP addresses
• b.To assign IP addresses to other hosts
• c.To forward traffic destined for remote networks✓
• d.To encrypt outbound traffic automatically

The default gateway is the router interface a host uses to reach destinations outside its local subnet. Without it, a host can only communicate on its own network. Traffic for remote networks is sent to the gateway for further routing.

Which frequency band and standard pairing offers wider channels and higher throughput but shorter range?

• a.2.4 GHz with 802.11b
• b.5 GHz with 802.11ac✓
• c.2.4 GHz with 802.11g
• d.900 MHz with 802.11ah

802.11ac operates in the 5 GHz band, offering wider channels and higher throughput at the cost of shorter range and less obstacle penetration. The 2.4 GHz band travels farther but is more congested and slower. Band selection balances speed against coverage.

Which protocol uses TCP port 22 to provide encrypted remote command-line access?

• a.Telnet
• b.FTP
• c.RDP
• d.SSH✓

SSH uses TCP port 22 to provide an encrypted remote shell, replacing insecure protocols like Telnet. Telnet on port 23 sends data in clear text. SSH is the standard for secure device management.

In a client-server architecture, what best describes the role of the server?

• a.It provides resources or services in response to client requests✓
• b.It only forwards broadcast traffic between subnets
• c.It exclusively resolves MAC addresses to IPs
• d.It generates spanning-tree topology changes

A server centrally provides resources or services such as files, web pages, or databases in response to client requests. Clients initiate requests and consume those services. This model contrasts with peer-to-peer where nodes act as both.

Which address is reserved as the IPv4 loopback used to test the local TCP/IP stack?

• a.192.168.0.1
• b.10.0.0.1
• c.127.0.0.1✓
• d.255.255.255.255

127.0.0.1 is the loopback address that lets a host test its own TCP/IP stack without touching the physical network. The entire 127.0.0.0/8 block is reserved for loopback. Pinging it confirms the local protocol stack is functioning.