CCST OSI and TCP/IP Models 2 — Questions and Answers
Question 1: Which OSI layer manages sessions between applications?
- Transport (Layer 4)
- Session (Layer 5) (Correct answer)
- Presentation (Layer 6)
- Application (Layer 7)
Correct answer: Session (Layer 5)
The Session Layer (Layer 5) manages communication sessions including setup, maintenance, and teardown.
Handles dialog control, synchronization checkpoints, and session recovery. Examples include NetBIOS, RPC sessions, and SIP for VoIP.
Question 2: At which TCP/IP model layer does HTTP operate?
- Network Access
- Internet
- Transport
- Application (Correct answer)
Correct answer: Application
HTTP operates at the Application layer, which combines OSI layers 5-7.
TCP/IP has 4 layers: Network Access, Internet, Transport, Application. HTTP uses TCP port 80/443. Other Application layer protocols include FTP, SMTP, DNS, SSH, SNMP.
Question 3: What is the primary function of the Presentation Layer (Layer 6)?
- To route packets
- To translate data formats, handle encryption, and compress data (Correct answer)
- To manage physical connections
- To segment data for transmission
Correct answer: To translate data formats, handle encryption, and compress data
The Presentation Layer translates between application format and network format, handling encoding, encryption, and compression.
Three functions: Translation (ASCII to EBCDIC, image formats), Encryption (TLS/SSL), Compression (video codecs). In practice, often performed within application code.
Question 4: Which PDU is associated with the Transport Layer?
- Bits
- Frames
- Packets
- Segments (Correct answer)
Correct answer: Segments
The Transport Layer uses segments (TCP) or datagrams (UDP) as its PDU.
PDU names by layer: L7-5 = Data, L4 = Segments/Datagrams, L3 = Packets, L2 = Frames, L1 = Bits. TCP segments contain ports, sequence numbers, ack numbers, window size, and flags.
Question 5: How does the TCP/IP model differ from the OSI model?
- TCP/IP has 4 layers mapping to OSI's 7, combining several layers (Correct answer)
- TCP/IP has 5 layers; OSI has 7
- Both have the same layers
- TCP/IP has more layers than OSI
Correct answer: TCP/IP has 4 layers mapping to OSI's 7, combining several layers
TCP/IP has 4 layers: Application (= OSI 5-7), Transport (= OSI 4), Internet (= OSI 3), Network Access (= OSI 1-2).
OSI is a theoretical framework; TCP/IP is practical and runs the modern internet. OSI provides granular layers better for discussing and troubleshooting specific functions.
Question 6: Which Network Layer protocol handles error reporting and diagnostics?
- TCP
- UDP
- ICMP (Correct answer)
- ARP
Correct answer: ICMP
ICMP provides error reporting (destination unreachable) and diagnostics (ping, traceroute) at Layer 3.
Key types: Type 0/8 (Echo Reply/Request for ping), Type 3 (Destination Unreachable), Type 11 (Time Exceeded for traceroute), Type 5 (Redirect). Can be exploited for reconnaissance so firewalls selectively filter it.
CCST OSI and TCP/IP Models 2
Which OSI layer manages sessions between applications?