OSI Model

What is layer 7 of the OSI model?

application

What layer number is the Application layer of the OSI model?

7

What is layer 6 of the OSI model?

presentation

What layer number is the Presentation layer of the OSI model?

6

At which OSI layer is encryption / decryption?

6 or presentation

At which OSI layer is data compression?

6 or presentation

What is layer 5 of the OSI model?

session

What layer number is the Session layer of the OSI model?

5

What is layer 4 of the OSI model?

transport

What layer number is the Transport layer of the OSI model?

4

What does MTU stand for?

maximum transmission (or transfer) unit

What is the typical value for MTU (in bytes)?

1500

At which OSI layer are software ports?

4 or transport

What does TCP stand for?

transmission control protocol

Which protocol provides for guaranteed delivery of information?

TCP, or Transmission Control Protocol

At which OSI layer is TCP?

4 or transport

Which protocol provides for fast (but not guaranteed) delivery of infor- mation?

UDP, or User Datagram Protocol

What does UDP stand for?

user datagram protocol

At which OSI layer is UDP?

4 or transport

At which OSI layer do we find segments?

4 or transport

What is the Protocol Data Unit at OSI layer 4?

segment

What is layer 3 of the OSI model?

network

What layer number is the Network layer of the OSI model?

3

At which OSI layer is the Internet?

3 or network

At which OSI layer are Wide Area Networks?

3 or network

What does WAN stand for?

wide area network

At which OSI layer is IP Addressing?

3 or network

At which OSI layer is Logical Addressing?

3 or network

At which OSI layer does a router operate?

3 or network

At which OSI layer does a gateway operate?

3 or network

At which OSI layer is Network Address Translation?

3 or network

At which OSI layer is Port Address Translation?

3 or network

At which OSI layer do we find packets?

3 or network

What is the Protocol Data Unit at OSI layer 3?

packet

What is layer 2 of the OSI model?

datalink

What layer number is the Data Link layer of the OSI model?

2

What does MAC stand for?

media access control

How does a typical laptop computer discover its own MAC address?

It already knows it. It is burned in on the network card.

At which OSI layer is the Local Area Network?

2 or datalink

At which OSI layer is MAC Addressing?

2 or datalink

At which OSI layer is Physical Addressing?

2 or datalink

At which OSI layer is Ethernet?

2 or datalink

At which OSI layer does a switch operate?

2 or datalink

At which OSI layer does a bridge operate?

2 or datalink

What is a multi-port bridge called?

switch

What is a two-port switch called?

bridge

At which OSI layer do we find frames?

2 or datalink

What is the Protocol Data Unit at OSI layer 2?

frame

What is layer 1 of the OSI model?

physical

What layer number is the Physical layer of the OSI model?

1

At which OSI layer is wireless signal?

1 or physical

At which OSI layer is coaxial cable?

1 or physical

At which OSI layer is cat5 cable?

1 or physical

At which OSI layer is fiber-optic cable?

1 or physical

What is a multi-port repeater called?

hub

What is a two-port hub called?

repeater

At which OSI layer does a hub operate?

1 or physical

At which OSI layer does a signal repeater operate?

1 or physical

At which OSI layer do we find bits?

1 or physical

What is the Protocol Data Unit at OSI layer 1?

bits

What is a software port?

A port is a number that indicates which computer program should receive the message.

What is a hop?

A hop is the moving of a packet from one LAN to another.

What does TTL stand for?

time to live

What is the purpose of TTL?

It reduces the risk of network loops.

What does having a routable address mean?

Packets can be sent to you by using your own IP address.

What are the five non-routable IP address blocks?

10.x.x.x, 127.x.x.x, 169.254.x.x, 172.16-31.x.x, and 192.168.x.x.

What does NAT stand for?

network address translation

What does PAT stand for?

port address translation

Explain Man In The Middle?

Man in the middle is (a) a hacking technique. (b) Two computers believe they are talking to each other. (c) Instead they are talking through (by way of) a third computer.

In NAT, how does the router remember the original sender?

The router keeps a table that matches outside port numbers with inside IP address and port number pairs.

What is garbage collection?

Garbage collection is a term for reclaiming resources that are no longer in use (or appear to be no longer in use). After collection, they can be

recycled and used for something else.

How long do NAT address pool entries last?

Address pool entries often expire (a) after ten minutes, or (b) when the table is full the most stale entry expires.

What is a keep-alive?

A keep-alive is a message that is sent between two computers just to keep the connection from timing out and being dropped.