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Network fundamentals - OSI models - ports and protocol

Network

Encompass a diverse range of connection extending to both wireless networks to wired networks

Clients

Devices users are going to access the network with

Servers

provide recourses to the network

hubs

old network devices that connect other devices like clients and servers over a local area network ( limits such as increased network errors due to broadcasting nature)

Switches

smarter hubs. Provide more security and more efficient bandwidth

Wireless access points (wap or ap)

allow wireless devices to connect to a wired network

routers

used to connect different networks together

firewalls

security barrier between internal network and external world (internet)

load balencers

devices or software that distribute network or app traffic across multiple servers

Proxy

acts as intermediary between a users device and the internet

Intrusion detection system (IDS)

Detect unauthorized access or anomalies and alert administrators

Intrusion prevention system (IPS)

Not only detect threats, but can also take action to prevent intrusion

controllers

In software defined networking (SDN). These are central units used to manage flow and control to networking devices

Network attached storage (NAS)

Dedicated file storage system that provides data access to a heterogeneous group of clients

Storage area networks (SAN)

high speed network that provides access to consolidated block level data storage

media

in networking, it refers to physical materials used to transmit data (cables and wireless signals)

Wide area network (WAN)

used to connect network over large geographical areas

client/server model

utilizes a dedicated server to provide access to network resources (files, scanners, printers) (backing up is easier) (centralized admin) (easier management) (better scaling) (opposite of peer to peer)

Peer to peer model

peers or other machines (laptops and desktops) can share resources together directly (low cost) (no specialized OS) (no dedicated resources) (No management) (poor scalability) (opposite of client/server )

Personal area network ( PAN )

Smallest type of wired or wireless network which covers a distance of 10 feet or less (bluetooth & USB hard-drive)

Local area network ( lan )

connects components in a limited distance (up to 100 meters ) (home)

Ethernet uses

IEE 802.3 standard

Wifi uses

IEE 802.11 standard

Campus area network ( CAN )

A building centric lan that is spread across numerous buildings in a certain area (college campus / business parks / military bases)

metropolitan area network ( MAN)

Connects locations that are scattered across the entire city

Wide area network ( WAN )

Connects geographically disparate internal networks (largest) (not always public) (connects 2 different businesses in different states)

Network topology

Refers to the arrangements of a different elements like links, nodes, clients, and servers that make up a computer network

physical topology

used to show how the network devices and components are physically cabled and connected together

logical topology

Talks about how the traffic is actually going to flow through our network

6 topologies

poiont to point - ring - bus - star - hub and spoke - mesh

point to point topology

simplest form of network topology - involves a direct connection between 2 devices

Ring topology

network configuration where each device is connected to 2 devices forming a circular path

Fiber distributed data interface (FDDI)

used to conduct data transmissions on fiber optic lines in a local area network (used with ring topology)

bus topology

all of the network devices are connected to a single central cable

star topology

one of the most common network layout that is used today ( all devices are connected to one centralized network. if that fails they all fail. if one of the connected fail, the network is still up unaffected )

hub and spoke topology

a variation of the star topology where the central node (hub) is connected to multiple nodes (spokes). Its like layovers. Data goes to stop somewhere (spoke) to eventually go to the final destination (node)

mesh topology

features point to point connection between every single device on the network to create a robust and redundant network

full mesh topology and calculation

every node is connected to every other node in the network ( ( n * ( n - 1 ) ) / 2 n is number of devices )

partial mesh topology

some nodes are organized in a full mesh scheme while others are only connected to one or two devices in the network

all topologies similarities and failures

point to point - simplest

bus - single points of failure

ring - single points of failure

star - central point failure

hub and spoke - central point failure

mesh - complex

infrastructure mode

the most common type of wireless network that uses a wireless access point as a centralized point

ad hoc mode

decentralized wireless network which creates peer to peer connection and does not require a router or access point

wireless mesh topology

an interconnection of different types of nodes and devices and radios ( combining bluetooth, cellular , wifi , satellite, microwave)

data center

any facility that businesses and other organizations use to organize, process, store, and disseminate large amounts of data

three tiered hierarchy

core , distribution/aggregation , access / edge (good for performance, management, scalability, redundancy ) ( 3 tier high way system )

collapsed core

network architecture where the core and the distribution layers are being merged into a single layer

spine and leaf architecture

an alternative type of network architecture that focuses on the communication within the datacenter itself ( can give faster speeds and lower latency ) ( 2 tier highway system )

spine and leaf - (spine)

connects switches in a full mesh topology

spine and leaf - (leaf)

consist of all the access switches

spine and leaf architecture can be used in a combination with the 3 tier hierarchy

true

traffic flows

north south / east west

north - south

traffic that enters or leaves the data center from the system physically residing outside the datacenter (Northbound traffic LEAVES datacenter) (SouthBound Enters datacenter)

east - west

refers to the dataflow within a datacenter

OSI model (open system interconnection model )

is a reference model

1. Physical (use term bits)

2. Data Link (use term frames)

3. Network (use term Packets)

4. Transport (use term Segments)

5. Session (use term data)

6. Presentation (use term data)

7. Application (use term data)

Physical Layer

OSI Layer 1 - Where transmission of bits across the network occurs and includes physical and electrical network characteristics

transition modulation (physical layer)

if it changes during the clock cycle, then 1 is represented. 0 otherwise (on or off)

2 cable standards inside our network (physical layer)

crossover cables - uses different cablings from both ethernet ports

straight through cables - uses equal cables from both ethernet ports

(TIA/EIA - 568A) - (TIA/EIA - 568B)

Asynchronous (physical layer)

Asynchronous - Uses a start and stop bits to indicate when the transmissions occur from the sender to the receiver ( like a voice mail )

Synchronous (physical layer)

Synchronous - uses a reference clock to coordinate the transmissions by both sender and receiver

broadband (physcial)

divide bandwidth into seperate channels ( tv channels)

Baseband (physical)

uses all available frequencies on a medium (cable) to transmit data (telephone) (uses reference clock)

Multiplexing (physical)

enables simultaneous usage of a baseband connection by multiple users ( at same time)

examples in physical layer

Layer 1 devices are essentially repeaters, passing along whatever is received

Dumb devices

fiber optic cable

ethernet cable

coaxial cable

bluetooth

wifi

NFC

hubs

access points

media converters

DataLink layer

OSI Layer 2 Packages data into frames and transmits those frames on the network

Switches

bridges

mac addresses

MAC Address (data link)

physical addressing system of a device which operates on a logical topology (unique 48-bit physical address assigned to every NIC produced) ( D2:51:F1:3A:34:65 ) (first 6 letters is the manufacturor) (last 6 is unique value)

LLC (data link)

provides connection services and allows acknowledgment of receipt of messages. Basic form of flow control

Isochronous (data link)

network devices use a common reference clock source and create time slots for transmission . Opposite of synchronous

Synchronous (data link)

Network devices agree on clocking method to indicate beginning and end of frames and can use control characters . Opposite of Isochronous

Asynchronous : (data link)

network devices reference internal clocks and use start and stop bits for synchronization

Layer 3 : Network

Uses IP and key word is Packets

Devices:

Routers and multi Layer switches (normal switches are layer 2 datalink)

IPV4 and IPV6 (most common on exam)

ICMP

Packet switching (Network)

Data is divided into packet and then forwarded

Circuit switching (Network)

Dedicated communication link is established between 2 devices

Message switching (Network)

Data is divided into messages which may be stored then forwarded

Route discovery and selection (Network)

manually configured as a static route or dynamically through a routing protocol (routers telling each other how to deliver info)

ICMP (network)

Sends error messages and operational information to an IP destination

Uses ping and traceroute and can be very vulnerable

meant for speed not data integrity. SO ITS ONLY FOR ERRORS AND UPDATES

Layer 4: Transport layer

Dividing line between upper layers and the lower layers of OSI

TCP and UDP

Windowing and buffering

firewall and load balancers

Key word : Segments

TCP (Transport)

Connection oriented protocol that is a reliable way to transport segments across the network

Is more serious and for more serious tools

it does that by breaking data into small packets

Another keyword: Segments , Connection Oriented, Flow control windowing, sequencing (1,2,3,4,5)

Threeway handshake TCP (Transport)

Making sure both sides are ready to communicate and communicate to say packets recieved

SYN

SYN-ACK

ACK

UDP (Transport)

Connectionless protocol that is an unreliable way to transport segments across the network

Good for audio and media streaming & increase performance

SMALLER THAN TCP PACKETS

Relies on ports

Another keyword: DataGram, Connectionless, No windowing , no retransmission, No sequencing (2 ,3 1, 5, 6) , Low LATENCY (means no delay and quick)

Windowing ( Transport)

Allows the clients to adjust the amount of data in each segment (speeding up and slowing down effeciently)

Buffer ( Transport)

Occurs when devices allocate memory to store segments if bandwidth is not available

Layer 5 Session layer

Key word DATA, NETBOIS, H.323 (ends calls)

Keeps conversations separate to prevent intermingling of data

Set up Session (Session)

Checking of user credentials and assigning numbers to sessions to help identify them

Maintain Session (Session)

Giving data to each other back and forth

Tear Down Session ( session)

Ending Session

RTP (H.323) (session)

Streaming audio / video

Netbios ( session)

Share files over a network

Layer 6 - Presentation Layer

Formats the data to be exchanged and secures that data with proper encryption

Scripting language (HTML Java), standard text, Pics

Key words : DATA, Data formatting (GIfs, ASCII, PIcs) and encryption

ASCII (data formatting) (presentation)

Text based language to use

Encryption ( Presentation )

Used to scramble the data in transit to keep it secure from others and provide confidentiality

Layer 7 Application

provides application level services where users communicate the computer

POP3, IMAP , SMTP, Service advertisement

Keywords: File transfer , network transfer, DATA

Application services ( Application)

Unites communicating components from more than one network application

Service advertisement (application)

Sending out of announcements to other devices on the network to state the services they offer

Encapsulation (Moving down in OSI layer from 7 to 1)

The process of putting headers around some data ( like closing a letter in an envelope)

Decapsulation (Moving up in OSI 1 to 7)

opening the headers around data

PDU

single unit of information transmitted in a computer network

SYN

Used to synchronize connection in 3 way handshake

ACK

used during 3 way handshake to acknowledge data recieved

FIN

used to tear down connections in 3 way handshake

RST

used when a client or server receives a packet that it was not expecting during the current connection