OSI

Question 1

OSI Layers

Answer 1

OSI- open systems interconnect

7. Application
8. Presentation
9. Session
10. Transport
11. Network
12. Data Link
13. Physical

Question 2

L1 responsibilities

Answer 2

Physical- Converts bits into voltage for data transmission, encoding and signaling

Question 3

L2 responsibilities

Answer 3

Data Link-
Logical Link Control (LLC) for linking to L3;
Media Access Control (MAC) for addressing;
Data framing; some error detection

Question 4

L3 responsibilities

Answer 4

Network- Provides:

• logical addressing;
• routing and path determination;
• datagram encapsulation;
• some error handling and diagnostics

Question 5

L4 responsibilities

Answer 5

Transport- Provides end-to-end data transport services and flow control.
Conducts error checking.

Question 6

L5 responsibilities

Answer 6

Session- Establishes manages and terminates connections between devices;
uses device names rather than addresses;

Question 7

L6 responsibilities

Answer 7

Presentation- Manages data format, compression and encryption

Question 8

L7 responsibilities

Answer 8

Application- provides user application services

Question 9

L1 PDU

Answer 9

Physical- Bits

Question 10

L2 PDU

Answer 10

Data Link- Frames (1.5Kb)

Question 11

L3 PDU

Answer 11

Network- Packets (65Kb) and Datagrams

Question 12

L4 PDU

Answer 12

Transport- Segments

Question 13

L5 PDU

Answer 13

Session- Data

Question 14

L6 PDU

Answer 14

Presentation- Data

Question 15

L7 PDU

Answer 15

Application- User Data

Question 16

L1 Devices

Answer 16

Physical- Cable, hub, modem, repeater (no addressing)

Question 17

L2 Devices

Answer 17

Data Link-
Switches (isolates collision traffic; some have VLAN ability),
Bridges,
NIC,
Brouter (hybrid bridge and router, routing packets to multiple protocols via IP or MAC);

Question 18

L3 Devices

Answer 18

Network-
Router (isolates broadcast traffic);
L3 switch (used for LAN cheaper than router);
Packet filter (Static/Stateless FW)- limited, all or nothing; blocks or allows entire protocol; opens/closes ports as needed

Question 19

L5 Devices

Answer 19

Session-
Circuit Level Gateway (monitors TCP handshake);
Stateful firewall inspects and understands traffic and allows protocols as long as they behave like they should

Question 20

L7 Devices

Answer 20

Application-
Gateways,
Application Proxies (slow),
Kernal Proxies (very fast and expensive hardware devices)

Question 21

L2 Protocols

Answer 21

Data Link- 
1- LLC (802.2)
2- Ethernet (802.3); 
3- Token Ring (802.5); 
4- WiFi (802.11);
5- FDDI & CDDI; 
6- PPTP; 
7- L2TP

Question 22

L3 Protocols

Answer 22

Network- 
IP; 
IPv6; 
IP NAT; 
IPSec; 
ICMP (ping, traceroute); 
RIP;

Question 23

L4 Protocols

Answer 23

Transport-
TCP,
UDP,
SSL/TLS (L4-L7)

Question 24

L5 Protocols

Answer 24

Session-
SQL,
RPC,
DNS (is L5 for exam)

Question 25

L6 Protocols

Answer 25

Presentation- No protocols; EFS (Encrypted File Sys)

Question 26

L7 Protocols

Answer 26

Application- 
FTP (on TCP), 
TFTP (UDP), 
SSH, 
IMAP, 
POP, 
HTTP/HTTPS