Domain 4 - Communications & Network Security

Question 1

OSI Reference Model

Answer 1

Open System Interconnect Layers:

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

Question 2

Physical Layer

Answer 2

Describes network hardware such as electrical signals, network interfaces, and cables. Hubs and repeaters are at this level.

Question 3

Data Link Layer

Answer 3

Describes data transfer between machines by Ethernet or other technologies like Token Ring. MAC (Media Access Control), LLC (Logical Link Control), switches and bridges are at this level.

Question 4

Network Layer

Answer 4

Describes data transfer between networks by IPv4 or IPv6. IP Addresses and Routers are at this level.

Question 5

Transport Layer

Answer 5

Describes data transfer between applications, flow control and error detection and correction. TCP (Transmission Control Protocol) and UDP (User Datagram Protocol) are at this level.

Question 6

Session Layer

Answer 6

Describes the handshake between applications like authentication processes.

Question 7

Presentation Layer

Answer 7

Describes the presentation of information like ASCII, JPEG, GIF and TIFF. Data conversion, character sets and image formats are at this level.

Question 8

Application Layer

Answer 8

Describes the structure, interpretation, and handling of information. In security terms, it is relevant because it relies on all the other layers.

Question 9

Logical Link Control (LLC)

Answer 9

Manages connections between two peers. It provides error and flow control and control bit sequencing. Used in Layer 2 - Data Link.

Question 10

Media Access Control (MAC)

Answer 10

Transmits and receives frames between peers. An Ethernet 48-bit hardware address is often referred to as a MAC address. Used in Layer 2 - Data Link.

Question 11

Internet Protocol (IP)

Answer 11

The most important network layer protocol and has two functions:
Addressing - Destination IP addresses are used to transmit packets through networks until the packet’s destination is reached.
Fragmentation - IP will subdivide a packet if its size is greater than the maximum size allowed on a local network.

Question 12

Routing Information Protocol (RIP)

Answer 12

A standard exchange of routing information among gateways and hosts. Uses distance vector algorithms to determine the direction and distance to any link in the internetwork. Hop count is the only routing metric used by RIP.
v1 allows a maximum hop count of 15 and allows updates at a programmable interval.
v2 adds cryptographic authentication and adds additional information.

Question 13

Open Shortest Path First (OSPF)

Answer 13

An interior gateway routing protocol for IP based on shortest route first or link state algorithm.

Question 14

Internet Control Message Protocol (ICMP)

Answer 14

ICMP's goals are to provide a means to send error messages from non-transient error conditions and to provide a way to probe the network in order to determine general characteristics about the network.
Functions:
1. Announce Network Errors
2. Announce Network Congestion
3. Assist Troubleshooting
4. Announce Timeouts

Question 15

Internet Group Management Protocol (IGMP)

Answer 15

Used to manage multicasting groups. There are three versions of this protocol that provide additional features.

Question 16

TCP Control Bits

Answer 16

URG - Urgent Pointer field significant
ACK - Acknowledgement field significant
PSH - Push Function
RST - Reset the connection
SYN - Synchronize sequence numbers
FIN - No more data from sender

Question 17

Border Gateway Protocol (BGP)

Answer 17

Created to replace Exterior Gateway Protocol (EGP) to allow fully decentralized routing.