Day 1 - Networks, Cables, OSI, and TCP Models Flashcards
What does
All People Seem To Need Data Processing
stand for?
Application Presentation Session Transport Network Data Link Physical
Application layer #?
7
Presentation layer #?
6
Session layer #?
5
Transport layer #?
4
Network layer #?
3
Data Link layer #?
2
Physical layer #?
1
What is the OSI model mnemonic?
All People Seem To Need Data Processing
What is the process of data moving down the OSI model called?
Encapsulation
What is the process of data moving up the OSI model called?
De-encapsulation
Define the Application Layer (7)
This layer is the closest layer to the end-user. The Application Layer usually provides services such as e-mail (SNMP and POP3), web browsing (using HTTP), and file transfer services (using FTP). The Application Layer determines resource availability.
Define the Presentation Layer (6)
The Presentation Layer presents data to the Application Layer. Multimedia works here, so think mp4, jpeg, gif, etc. Encryption, decryption, and data compression also take place at this layer.
Define the Session Layer (5)
The role of the Session Layer is to set up, manage, and terminate sessions or dialogues between devices. These take place over logical links, and what is really happening is the joining of two software applications. SQL, RPC, and NFS all work at the Session Layer.
Define the Transport Layer (4)
The role of the Transport Layer is to break down the data from the higher layers into smaller parts, which are referred to as segments (at this layer). Virtual circuits are set up here, which are required before devices can communicate.
What are the three methods used to control data flow?
▪ Flow control
▪ Windowing
▪ Acknowledgements
What is Flow Control?
If the receiving system is being sent more information than it can process, it will ask the sending system to stop for a short time. This normally happens when one side uses broadband and the other uses a dial-up modem. The packet sent telling the other device to stop is known as a source quench message.
What is Windowing?
With windowing, each system agrees upon how much data is to be sent before an acknowledgment is required. This “window” opens and closes as data moves along in order to maintain a constant flow.
What are Acknowledgements?
When a certain amount of segments is received, the fact that they all arrived safely and in the correct order needs to be communicated to the sending system.
What is the Three-Way Handshake?
This is where you send a packet to establish the session. This first packet is called a synchronise (SYN) packet. Then the remote device responds with a synchronise acknowledgement (SYN-ACK) packet. The session is established in the third phase when an acknowledgement (ACK) packet is sent.
Which service does the Three-Way Handshake use?
TCP service
What are the two most widely known Transport Layer protocols?
Transmission Control Protocol (TCP)
User Datagram Protocol (UDP)
What are the main characteristics of TCP
Reliable connection-oriented protocol
Uses three-way handshake
Uses windowing
What protocols use TCP?
Telnet
HTTPS
FTP
What are the main characteristics of UDP?
Connectionless protocol
Smaller packets
Conserves time and network resources
What is an example of a protocol that uses UDP?
TFTP
Define the Network Layer (3)
The Network Layer takes the segments from the Transport Layer and breaks them down into smaller units called packets. The Network Layer must determine the best path to take from one network to another; for this reason, routers work at this layer. Routers use logical addressing here, and TCP/ IP addressing is called IP addressing.
Define the Data Link Layer (2)
The Data Link Layer chops down packets into smaller units referred to as frames. Layer 2 switches work at this layer and use hardware or MAC addresses, so they can switch traffic much faster because there is no need to check IP addresses and routing tables. WAN protocols work at Layer 2, including HDLC, ISDN, and PPP. Ethernet also works at Layer 2. In order to interface with the upper and lower levels, the Data Link Layer is further subdivided into the Logical Link Control (LLC) Sublayer and the Media Access Control (MAC) Sublayer. The LLC Sublayer interfaces with the Network Layer and the MAC
Define the Physical Layer (1)
At this layer, frames are converted into bits for placing on the wire. These bits consist of electrical pulses, which are read as “on” and “off” bits, or in binary 1s and 0s, respectively. Hubs work at this layer, and here is where you will find cable specifications, such as RJ45.
What is the four layer TCP/IP DoD Model?
Application (4)
Transport/Host-to-Host (3)
Internet or Internetwork (2)
Link/Network Interface (1)
What is the five layer TCP/IP DoD Model?
Application (5) Transport (4) Network (3) Data Link (2) Physical (1)
What is the encapsulation and data called at the Application Layer?
Data, but not encapsulated yet.
What is the encapsulation and data called at the Transport Layer?
TCP header added to the data.
Data is called a Segment
What is the encapsulation and data called at the Network Layer?
IP header added (including IP address).
Data is called a Packet
What is the encapsulation and data called at the Data Link Layer?
Data Link header added (Data Link address).
Data is called a Frame
What is the encapsulation and data called at the Physical Layer?
Data is turned into electrical signals.
Data is called Bits on the wire
What is TCP/IP?
TCP/ IP is a complete suite of protocols and services which enable communication to take place over networks.
What layer does TCP operate at in the OSI model?
Transport Layer
What is the TCP port for FTP Data?
20
What is the TCP port for FTP Control?
21
What is the TCP port for SSH?
22
What is the TCP port for Telnet?
23
What is the TCP port for SMTP?
25
What is the TCP port for DNS?
53
What is the TCP port for HTTP?
80
What is the TCP port for POP3?
110
What is the TCP port for NNTP?
119
What is the TCP port for NTP?
123
What is the TCP port for TLS/SSL?
443
At what OSI layer does Internet Protocol (IP) operate?
Network Layer
Define Internet Protocol (IP)
IP operates at the Network Layer of the OSI model. It is connectionless and is responsible for transporting data over the network. IP addressing is a function of Internet Protocol. IP examines the Network Layer address of every packet and determines the best path for that packet to take to reach its destination.
Define User Datagram Protocol (UDP)
UDP transports information between network devices but, unlike TCP, no connection is established first. UDP is connectionless, gives best-effort delivery, and gives no guarantee that the data will reach its destination.
At what OSI level does User Datagram Protocol (UDP) operate?
UDP operates at the Transport Layer of the OSI model.
Both TCP and UDP are carried over what protocol?
IP
When is UDP preferred over TCP?
For applications in which low latency is preferred over reliability or guarantees.
What are three common UDP protocols and their related port numbers?
DNS 53
TFTP 69
SNMP 161/162
At what OSI layer does FTP operate at?
Application Layer
What protocol does FTP use for data transfer?
TCP
What is the command to debug FTP traffic?
debug ip ftp
What protocol does SMTP use?
TCP
What is the command to debug HTTP traffic?
debug ip http
What is the only utility that can check all seven layers of the OSI model?
Telnet
What is the command to quit an inactive telnet session?
Ctrl Shift 6 then X
What is the debug command for Telnet?
debug telnet
What does ICMP stand for?
Internet Control Message Protocol
What is ICMP used for?
ICMP is a protocol used to report problems or issues with IP packets (or datagrams) on a network.
What happens when a problem is experienced with an IP packet?
The IP packet is destroyed and an ICMP message is generated and sent to the host that originated the packet.
ICMP delivers messages inside ?
IP packets