CCST Level 3 — Questions and Answers
Question 1: Which Cisco IOS command displays the currently running configuration?
- show startup-config
- show running-config (Correct answer)
- show version
- show flash
Correct answer: show running-config
The 'show running-config' command displays the active configuration in RAM.
Running-config (RAM) vs startup-config (NVRAM). Changes affect running-config immediately. Save with 'copy running-config startup-config' or 'write memory'.
Question 2: What is the purpose of the subnet mask in IPv4 networking?
- To encrypt network traffic
- To divide an IP address into network and host portions (Correct answer)
- To assign IP addresses automatically
- To translate domain names
Correct answer: To divide an IP address into network and host portions
A subnet mask determines which bits identify the network and which identify the host.
Devices perform bitwise AND between IP and mask to determine network address. Used to decide if destination is local or remote. Subnetting subdivides networks for organization and security.
Question 3: Which OSI layer handles logical addressing and routing?
- Layer 1 - Physical
- Layer 2 - Data Link
- Layer 3 - Network (Correct answer)
- Layer 4 - Transport
Correct answer: Layer 3 - Network
Layer 3 (Network) handles IP addresses and routing between different networks.
Functions: logical addressing (IP), routing (OSPF, EIGRP, BGP), and packet fragmentation. Key devices: routers and Layer 3 switches. Protocols: IPv4, IPv6, ICMP, IPsec.
Question 4: What does the TCP three-way handshake establish?
- A UDP connection
- A reliable connection between two hosts using SYN, SYN-ACK, and ACK messages (Correct answer)
- An encrypted tunnel between routers
- A VLAN trunk between switches
Correct answer: A reliable connection between two hosts using SYN, SYN-ACK, and ACK messages
The three-way handshake (SYN, SYN-ACK, ACK) synchronizes sequence numbers and establishes a reliable connection.
Client sends SYN with initial sequence number. Server responds SYN-ACK with its own sequence number. Client sends ACK. Both sides agree on sequence numbers. Connection terminated with four-way FIN handshake.
Question 5: What is the function of DHCP in a network?
- To resolve domain names
- To automatically assign IP addresses and network configuration to devices (Correct answer)
- To route packets between networks
- To encrypt data during transmission
Correct answer: To automatically assign IP addresses and network configuration to devices
DHCP automatically assigns IP addresses, subnet masks, gateways, DNS servers, and other parameters.
Uses DORA process: Discovery, Offer, Request, Acknowledgment. Leases are temporary. Prevents IP conflicts by centrally managing the address pool.
Question 6: Which wireless security protocol provides the strongest encryption for modern Wi-Fi?
- WEP
- WPA
- WPA2
- WPA3 (Correct answer)
Correct answer: WPA3
WPA3 offers SAE authentication, protection against offline dictionary attacks, and forward secrecy.
Evolution: WEP (cracked) -> WPA (TKIP, temporary) -> WPA2 (AES-CCMP) -> WPA3 (SAE + PMF + forward secrecy + 192-bit enterprise). WPA3 mandates Protected Management Frames.
CCST Level 3
Which Cisco IOS command displays the currently running configuration?