IT 366 Review Lecture 1

At each layer, the unit of data has a different name. Can you name some (especially at layers 2, 3)?

Application Layer: Data/Message Transport Layer: Segment Network Layer: Packet Data Link Layer: Frame Physical Layer: Bits

Physical Layer

Mechanical and electrical interface. wires, cord

Why is it impractical to manage point-to-point connections between devices (except for a trivially small number of them)?

unplugging from one device and plugging to another device and having to do this numerous times is a hassle

What is an alternative to client-server? How is it different?

An alternative to this model is the Peer-to-Peer Model. Each computer is a peer (equal) to the others involved. Each system may act like a server (waiting for requests and responding) and a client (sending requests and waiting for responses).

What is an attack in this context? What does it require?

An attack is a deliberate attempt to violate security. An attack requires intent, which presupposes that a person is responsible for it (malicious intent is required). An animal biting through a network cable is a 'threat' - a person meaning to intrude on a network is an 'attack'.

What is the client-server model? How does it work?

At the Application Layer, the client-server model is commonly used. A client is typically an end user's platform (hardware/software combination); it sends requests to a server and receives responses.

Presentation Layer

Formatting of data at the syntax level

What is TCP/IP? Why is it named "TCP/IP"?

Gets its name from two of the protocols that belong to it: Transmission Control Protocol/Internet Protocol. Most common implementation of a layered architecture for data communication

What is a security mechanism? What is a pervasive mechanism? What is a specific mechanism?

Something we implement in an attempt to provide one or more required security services. operate at one layer in the communications process operate across across several layers or an entire system

Why is a "perfect" security solution not practical?

There is a trade-off between security and usability - a system with total security would have no useful purpose, and vice versa.

Data link Layer

This layer bridges the networking media with the Network layer. Its primary function is to divide the data it receives from the Network layer into frames that can then be transmitted by the Physical layer.

Transport Layer

movement of data in a reliable manner from one system to another

Does the term "network" include the computers attached to networking devices?

no

OSI Reference Model

theoretical tool for describing interconnections between software applications on two systems. Seven Layers. Upper 6 describe software functionality.

What is the cardinality (number-to-number) of the relationship between services and mechanisms? Can you explain why?

Many-to-Many; Many services may be offered by a mechanism, and many mechanisms can provide a service.

What data values are used to identify the source and destination at different layers?

A switch uses the MAC address of a network interface to identify a device. A router uses an IP address to route packets. TCP and UDP use a port number to identify a service.

What is the relationship between a threat and an attack?

A threat can be anything that could possibly violate security (nature, etc.), and an attack requires malicious intent (presumably by a person or entity).

What is a threat in this context? Is it certain to occur?

A threat is a potential violation of security - anything that represents a possible compromise of security is considered a threat; it is not certain to occur. A meteor hitting a server farm can be considered a threat.

Application Layer

End user interacts with various applications. (IE, Chrome, Firefox). Data is exchanged through between ________ and its users

Session Layer

Establishes, maintains, and manages sessions between systems

What is the actual path for data moving in or out of a layer?

In reality, data moves up and down between layers, except at physical

What should be specified in a policy document?

Information assets should be identified Document should explain, for each asset: why each is important to the organization What security services it needs How these services will be implemented

Network Layer

Routers operate here. defines the processes used to route data across the network and structure and use of logical addressing.

How many layers will be used in a switch? A router? A gateway application? A server?

Switch: Data link Layer (1) Router: Network Layer (1) Gateway Application: Application layer (1) Server: Application ,presentation,session (many)

What is the conceptual relationship between layers in two communicating systems?

conceptually, each layer communicates with its peer on the other side