Week 3 Transport Layer Flashcards
What is multiplexing?
Multiplexing is converting multiple signals of traffic into a single signal
What is demultiplexing?
Demultiplexing is taking the 1 multiplexed signal and converting it back to the separate, original signals back to the specific service using its port
What does the transport layer use to perform multiplexing and demultiplexing?
The transport layer uses ports to perform multiplexing
Describe what ports are?
Ports are a 16-bit number that direct traffic to specific services on a networked computer
What’s a socket address/socket number?
A socket address/socket number is the port number added to the end of an IP address through the use of a colon :
What is FTP?
File Transfer Protocol
an older method of transferring files between computers
What port does FTP listen on?
Port 21
What is a TCP segment made of?
TCP header and data payload
What does an Ethernet frame encapsulate?
Ethernet frame encapsulates IP datagram
What does an IP datagram encapsulate?
IP datagram encapsulates TCP segment
Name the 13 sections of a TCP segment
- source port 16
- destination port 16
- sequence number 32
- acknowledgment number 32
- header length/data offset field 4
- empty 6
- control flags 6
- TCP window 16
- checksum 16
- urgent 16
- options 0-16
- padding
- data payload (varies)
Why is a source port important?
Keeps communication lines organized and so the traffic knows where to come back to when it fetches data requested by the client
What does buffer mean?
A buffer is when data is held somewhere before being sent somewhere else
What are the 6 TCP control flags?
- URG urgent
- PSH push
- ACK acknowledge
- SYN synchronize
- FIN finish
- RST reset
Describe the 3-way handshake (control flags)
A sends SYN to B
B sends SYN/ACK to A
A sends ACK to B
Describe the 4-way handshake
B sends FIN to A
A sends ACK to B
A sends FIN to B
B sends ACK to A
Describe what is a handshake
a handshake is a way for 2 devices to make sure they’re using the same protocol to understand each other
What does it mean when a connection is a full duplex?
When a TCP connection has been established through the 3-way handshake
What are the 7 socket states?
- LISTEN
- SYN_SENT
- SYN_RECEIVED
- ESTABLISHED
- FIN_WAIT
- CLOSE_WAIT
- CLOSED
What is a socket?
creates a new endpoint (back and forth) in a potential TCP connection
(an active port used by a service)
What is instantiation?
Instantiation means to create a new instance of something
What does a socket require?
a program
A connection can only be established to a program if it has opened ____ on its ____?
if it has opened a socket on its port
What is a connection-oriented protocol?
a connection-oriented protocol uses the connection established to make sure that all the data has been properly delivered
What code does the TCP segment contain?
the ports used to establish a network connection
How does a TCP segment ensure data integrity?
- sends what port is used in a connection
- performs a checksum
- sends ack between service and client to show data was received
What’s the difference between system ports, user ports, and ephemeral ports?
- System 1-1023 common applications, modern OS don’t use this for outbound traffic
- User 1024-49151 vendor registered for specific server apps
- Ephemeral 49152 - 65535 temp ports for private transfers for clients
What are firewalls?
run on individual hosts to block certain traffic/ports
