The Bits and Bytes of Computer Networking 3 Flashcards
What is the role of the Transport Layer?
Directs traffic to specific network applications.
What is multiplexing / demultiplexing and where are they handled?
Multiplexing - the sending node can direct traffic towards the specific receiving service.
Demultiplexing - on the receiving node, delivering the incoming traffic to the right service.
Handled by ports.
What is a port, and how is one specified?
Software based, each port is identified by a 16 bit number, the computer knows what kind of traffic is incoming and where it should go, depending on what port it arrives to. Specified after an IP address, following a colon, eg, 9.100.100.0 : 80
What are ephemeral ports?
When a device is requesting data, it specifies a return port of a very high number, so that it can keep all incoming data separate.
What are the 6 TCP control flags and what does each mean?
1 URG = urgent, indicates if the segment is urgent, with a value of 1, if so check urgent pointer field for more info.
2 ACK = acknowledgement, a value of 1 here indicates that the acknowledgement field should be examined.
3 PSH = push, this segment should be sent to the application immediately, instead of being buffered (held somewhere else)
4 RST = reset, information has been lost, need to start again.
5 SYN = synchronize, used when establishing a connection, tells to check the sequence number field for order of segments.
6 FIN = finish, when FIN=1, data is all sent and connection will be closed.
What is a packet at the transport level called?
A TCP segment.
What is a 3 way handshake? When is it used and what is the process?
Used when establishing a TCP connection, uses TCP control flags. Process = >SYN, ACK.
What is a 4 way handshake? When is it used and what is the process?
Used when establishing a TCP connection, uses TCP control flags. Process = ACK, >FIN,
What is a socket in a TCP connection?
The instantiation of an end-point in a potential TCP connection.
What is instantiation?
The actual implementation of something defined elsewhere.
How does a TCP socket become instantiated and what does this mean?
It needs an application to open a socket on that port in order for it to function. You can send traffic to any port but will only get a response if that socket has been instantiated / activated.
What are 7 states that a TCP socket can be in, what do they mean, and which side are they observed on (client / server)?
LISTEN = the socket is ready and listening for incoming connections, only seen on server side.
SYN_SENT = a SYN request is sent but no connection established yet, only on client side.
SYN_RECEIVED = a SYN request has been received, and a SYN/ACK has been sent back. Only server side.
ESTABLISHED = TCP connection established, both sides free to send data. Seen on client and server.
FIN_WAIT = FIN has been sent but no ACK received. Seen on client and server.
CLOSE_WAIT = TCP connection ended, however application has not released the socket yet. Seen on client and server.
CLOSED = connection fully terminated. Seen on client and server.
What are the differences between TCP and UDP?
TCP = establishes a connection. Uses a constant stream of ACKS to ensure all sent data has been received. Less risk of data lost, but more traffic and is overall slower.
UDP = No connections / ACKS, just set the port and send the packet. Faster but less reliable.
What are the 3 types of ports, and what kind of service is each used for? What are the numbers of the first type?
0 - 1023 = Well known ports / system ports - used for well known network services.
Registered ports - less common network services.
Ephemeral ports - used for establishing outbound connections.
What is a Firewall?
A network security system that monitors and controls incoming and outgoing network traffic based on predetermined security rules.
What is one of the main protocols that is used with web browsers at the application layer?
HTTP - Hyper Text Transfer Protocol - is the foundation of data exchange on the web, allows the fetching of resources, eg html files.
In the OSI model, what is the role of the session layer?
Takes the application layer data and gives it to the presentation layer.
In the OSI model, what is the role of the presentation layer?
Ensures the data being sent will be able to be understood by the receiving application. Handles encryption and compression of data.
In the OSI model, what is the role of the application layer?
Used by end-user software such as web browsers and email clients.
What does OSI stand for?
Open Systems Interconnection.
What does TCP stand for?
Transmission Control Protocol.
What does UDP stand for?
User Datagram Protocol.
