Chapter 1 - Internetworking Flashcards
What does OSI stand for?
Open Systems Interconnections Model
What is an internetwork?
When you connect two or more networks via a router and configure a logical addressing scheme such as IP or IPv6
What is network segmentation?
Breaking up a massive network into a number of smaller ones
What is a hub?
- They connect network segments together.
- They don’t segment networks
What type of network device would you use to break up a collision domain?
A switch
What is a broadcast?
A broadcast means that a network delivers one copy of a packet to each destination
What 6 things commonly cause LAN traffic congestion?
- too many hosts in a collision or broadcast domain
- broadcast storms
- too much multicast traffic
- low bandwidth
- adding hubs for connectivity to the network
- a bunch of ARP broadcasts
What type of network device would you use to break up a broadcast domain?
A router
What are the 2 advantages to using a router in your network?
- They don’t forward broadcasts by default
- They can filter the network based on layer 3 information such as the IP address
What are the 4 ways a router functions in your network?
- Packet switching
- Packet filtering
- Internetwork communications
- Path selection
What is a routing table?
A routing table is a map of your internetwork, used to make best path selections to get data to its proper destination and forward packets to remote networks
What are the functions of a switch?
- Employed to add functionality to a network LAN
- Optimise performance by providing more bandwidth
- They switch frames from one port to another within the switched network
What is a collision domain?
- A scenario where one device sends a packet out on a network segment and every device on that network segment is forced to listen to it.
- If each device tries to transmit a collision will occur.
- Each and every port on a switch represents a collision domain allowing data to flow more smoothly
What is a switch?
They create separate collision domains within a broadcast domain
What do the top 3 layers of the OSI model do?
They define how applications within the end stations will communicate with each other as well as users.
What do the bottom four layers of the OSI model do?
They define how data is transmitted end to end
What is the application layer?
- It provides a user interface.
- Identifying and confirming the communication partners availability.
- Verified required resources
- Applications like Word don’t reside at the application layer, but rather interface with the application layer protocols
- Some applications that do reside at application layer include Telnet, FTP, TFTP
What is the presentation layer?
- It presents data and handles processing such as encryption and compression
- Responsible for data translation and code formatting
- Ensures that data transferred from the application layer of one system can be read at the application layer of another
What is the session layer?
- Responsible for setting up, managing and dismantling sessions between presentation layer entities.
- Keeps different applications data separate.
- Communication co-ordinated via 3 different modes:
- Simplex
- Half Duplex
- Full Duplex
What is simplex communication?
One way communication
What is half duplex communication?
Two way communication with only one way taking place at a time preventing interruption
What is full duplex communication?
Devices can transmit and receive at the same time
What is the transport layer?
- segments and reassembles data into a single data stream
- services at this layer take data from upper layer applications and combine into one concise data stream
- provides end to end data transport services and can establish logical connection between source and destinations hosts
- uses TCP and UDP
- can also hide details of network dependent information from higher layers and provide transparent data transfer
- can be connection oriented or connection less
What does reliable networking mean?
- means acknowledgements, sequencing and flow control will be used
- used at transport layer
What is connection oriented communication?
- must establish connection before sending of data
- three way handshake
What are the steps in a three way handshake?
- SYN (synchronisation) - connection agreement
- SYN ACK (acknowledgement) - acknowledges request, establishes connection parameters, receivers sequencing synchronised so bi-directional connection can be established
- ACK - notifies destination host that connection has been accepted and established. Data transfer can begin
What is flow control? (2)
- ensures data integrity at the transport layer by allowing applications to request reliable data transport between systems
- prevents host on one side from overflowing buffers on the other
What 4 things will reliable data transport achieve?
- segments delivered are acknowledged back to sender
- segments not acknowledged are re-transmitted
- segments are sequenced back in order upon destination
- manageable data flow maintained to avoid congestion, overflowing, data loss
What is the purpose of an indicator with regards to flow control?
Allows receiving hosts buffer to indicate to sender to stop sending data until current data has been processed
What are the four characteristics of a connection oriented transfer?
- uses 3 way handshake
- uses sequencing
- acknowledges connection
- uses flow control
What are the 3 types of flow control?
- buffering
- windowing
- connection avoidance
What are windows?
It is the quantity of segments, measured in bytes that the transmitting machine is allowed to send without receiving an acknowledgement
What are the two window sizes that can be used?
1 and 3
What happens to data transfer with a window size of 1?
Sending machine will wait for an acknowledgement for each data segment in transmits before transmitting another
What happens to data transfer with a window size of 3?
Allows 3 segments to be transmitted before sending an acknowledgement
What is positive acknowledgement with re-transmission?
- requires a receiving machine to communicate with the transmitting source by sending an acknowledgement message to the sender when it receives the data
- sender documents each segment measured in bytes and then sends and waits for acknowledgement before sending next segment
- when sending a segment, transmitting machine starts a timer and re-transmits segment if no acknowledgement is received
What is session multi-plexing?
- transport layer working in tandem with session layer
- separates data from different applications
- happens when a client connects to a server with multiple browser sessions open
- client data from each browser session must be separate when the server application receives it
What is the network layer?
- manages device addressing
- tracks location of devices on the network
- determines best way to move data
Which layer of the OSI model is responsible for transporting traffic between devices that aren’t locally attached?
Network layer
Which network device is used at layer 3?
Router