Network Models Flashcards by William Carosella

OSI Layer Model

7: Application
6: Presentation
5: Session
4: Transport
3: Network
2: Data Link
1: Physical

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Layer 1

Physical layer - the cabling used to connect

Also a hub, if it’s an old network setup

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Layer 2 Sublayers

Only layer with sublayers

2a: Logical Link Control (LLC)
-Aspect of NIC that talks to OS (via drivers). Handles network protocols and flow control

2b: Media Access Control
-MAC encapsulation - creates and addresses the frame and performs frame check sequence (FCS)

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NIC

Network Interface Card

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MAC Address

Media Access Control - burned into a NIC’s ROM chip

48 bits - 12 hex characters

Companies request a block of MAC addresses to use

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Unix vs Windows MAC

Windows uses dash
use ipconfig /all to find

Linux uses colons
ifconfig (Macintosh)
ip a (linux)

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OUI

Organizationally Unique Identifier - the first 6 digits of a MAC address

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Device ID

Last 6 digits of MAC address, represent the serial number from manufacturer

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EUI-48

Extended Unique Identifier - just another name for a MAC address

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Layer 2 Frame Encapsulation

Recipient MAC | Sender MAC | Type of Data | Data | FCS

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Frame Header

MAC addresses (recipient/sender) and Type

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Frame Payload

Encapsulated Data

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Frame Trailer

FCS - Frame Check Sequence.

Uses cyclic reduncancy check (CRC) for receiving NIC to verify data

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Frame data limitations

1500 bytes
FCS is always 4 bytes

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Data stored by NICs

MACs of devices they have previously communicated with

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FF-FF-FF-FF-FF-FF

Broadcast MAC address, NIC sends out to all devices when requesting MAC addresses, will receive a response with the MAC

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Process for Frame Movement

1) NIC receives data from OS
2) NIC attaches FCS to data
3) NIC attaches header
4) Frame sent

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Devices at Layer 2

Anything dealing with MAC addresses

Switches, NICs

Network Protocol

Establishes the unique identifiers for each system
Creates set of communication rules for data handling

Logical Addressing

Hardware independent addressing on a network.

Layer 3

Network Layer

Deals with IP addresses

Packets

The data that gets placed within a frame by the NIC

Has own encapsulation: Header (dest. IP and source IP) and Data

Router

Allows communications across networks, including those that do not rely on Ethernet

IP Packet Syntax

Dest. IP - packet header
Source IP - packet header
Data

Router's relationships to frames

Each router strips frame from packet, reads packet header (destination IP), then reattaches a new frame to send to subsequent MAC (or other format) based in the destination IP and network type

Layer 4

Transport Layer

Segmentation

Dividing up data into quantities that fit into packets and their container frames. Creates segments and assigns sequence numbering. The serving system performs this

Reassembly

The receiving system performs this Putting the segmented data back together into a sensible whole and verify data is not corrupted

Transport Protocol Purpose

Segmenting data and assigning them sequence numbers

TCP Segment

Inside of the frame and inside the packet, after the IP header but before the data. Includes necessary transport information so data arrives in good order

UDP Datagram

Does not utilize as many tools as TCP segment, does not verify that receiving system gets data.

Layer Five

Session Layer

Manages and handles sessions over a network. Sessions connect applications to other applications. Think designated lanes for connections.

Layer 6

Presentation Layer

Data translation into a format usable by an Application and vice versa

Layer 7

Application Layer

APIs - allow applications to be network aware

API

Application Programming Interface

TCP definition and orientation

Transmission Control Protocol Connection-oriented

UDP definition and orientation

User Datagram Protocol Connectionless

TCP Segment Syntax

UDP datagram syntax

source port | Destination Port | Length | Checksum | Data Notice the source and dest are reversed order compared to IP and MAC headers

Layer 2

Data Link Layer