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03. How the TCPIP Model Actually Works.md

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+---
+id: 03. How the TCPIP Model Actually Works
+aliases: []
+tags:
+  - CCNA
+---
+# How the TCPIP Model Actually Works
+
+## Protocols and Standards
+
+A [[Protocol]] is a set of rules defining how data should be communicated between devices over a [[network]].
+  - The "Languages" that computers use to communicate.
+Since the early days of computer networking, there have been several attempts to define the functions needed for computers
+to communicate with each other
+  - Often developed by a specific vendor (e.g, [[IBM]]) to be used with their own products.
+  - With a proprietary approach, enabling communications between different vendor's products was difficult.
+A [[standard]] is an agreed-upon specification that describes how a protocol or technology should work
+  - With vendor neutral standards, devices of all types can communicate with each others.
+  - An [[Apple]] Macbook can access a [[website]] hosted on a web server running [[Linux]].
+  - A PC running [[WIndows]] can send an email that can be read on a smartphone running [[Android]]
+
+## A bit of history
+
+Early work on the computer netowrks that would evolve into today's [[Internet]] began in the [[1960]]s
+- The [[US]] Department of Defense's [[ARPA]] funded ARPANET, which came online in 1969 to connect mainframes at universities and labs
+- Originally used a protocol called [[NCP]] 
+Vint Cerf and Bob Kahn (working on DARPA) began developing [[TCP]] in 1974
+- Later divided into two protocols still used today:
+  - [[TCP]]
+  - [[IP]]
+THese two protocols form the fundation of the protocol suite known as [[TCP/IP]] today
+  - ARPANET fully switched to TCP/IP in January 1, 1983.
+TCP/IP became dominant over vendor-proprietary solutions at the time because it was published as a set of open
+standards that any vendor could implement, and it could run over many different types of networks.
+
+## Who defines the standards?
+
+Most netwoking standards are developed by independent standards organizations, not by a single vendor, with participation from engineers at many companies
+- [[IEE]] (Institute of Electrical and Electronics Engineers)
+  - Develops many of the technologies used on local area netowrks:
+    - [[Ethernet]] (802.3)
+    - [[WIFI]] (802.11)
+- [[IETF]] (Internet Engineering Task Force)
+  - Open community that defines [[protocols]] used on the [[Internet]]
+    - [[TCP]], [[IP]], [[UDP]], [[HTTP]], [[DNS]], etc.
+  - Publishes standards in document called [[RFC]]'s (Requests for Comments)
+
+## Layered models
+
+Networks do a lot of different jobs to move data from one computer to another.
+  - Physical transmission of signals, local delivery on a [[LAN]], routing traffic between networks, end-to-end conversations, applications, etc.
+A model lets us group related jobs into layers.
+  - Each layer has a specific role.
+  - Each layer uses the services of the layer below and provides services to the layer above
+Protocol live (mostly at one layer)
+  - Examples later: IP, TCP, HTTP, etc.
+  - Together they form a stack of protocols that work as a team (the network stack)
+
+1. Application Layer : telnet, FTP, TFTP
+2. Transport Layer: TCP, UDP
+3. Internet Layer: IP, [[ICPM]]
+4. Link Layer: cables, WIFI
+
+The model is description, not a law.
+  - Different textbooks/courses use slightly different models (4-layer, 5 layer...)
+
+## TCP/IP Layers
+
+### Layer 1 : the physical layer
+
+- The physical Layer (Layer 1) sends and receives bits as electrical, optical, or radio signals over the medium
+- Defines things like cables, connectors, signal levels, and link speeds.
+- Examples: copper UTP cables, fiber-optic cables, WI-FI radios and antennas, network interface cards [[NIC]]'s
+  - The physical aspects of transmitting data are very complex
+  
+### Layer 2 : Local Network Layer
+
+- The Local Network Layer provides hop to hop delivery of messages on a local network.
+  - A hop is one step along the path between two devices:
+    - From one router or host, to the next router or host in the path
+  - [[Switches]] don't countL a switch just extends the local network, allowing multiple devices to connect.
+- Uses [[MAC]] addresses to identify interfaces.
+- Protocols at this layer includes
+  - Eternet
+  - Wifi
+
+### Layer 3 : The Internet Layer
+
+- The Internet Layer provides end-to-end delivery between hosts across multiple networks
+- Uses IP addresses to identify hosts in the network.
+- Routers operate mainly at this layer, using the message's destination IP address to forward the message toward its final destination host
+- Protocols at this layer includes
+  - IP ([[IPv4]], [[IPv6]])
+  - [[ICMP]]
+
+### Layer 4 : The Transport Layer
+
+- The Transport Layer provides end-to-end communication between application processes.
+  - Also called "process to process" or "service-to-service"
+- Uses port numbers to identify the processes on each host.
+- Runs mainly on the communicating hosts; routers normally operate based on IP, not on Transport layer informations
+- Protocols at this layer includes
+  - UDP
+  - TCP
+
+
+### Layer 5 : Application Layer
+  
+- The application Layer is where network communications meet applications.
+  - Usually called Layer 7
+- Defines how application processes format, send, and interpret data
+- Protocols at this layer define message formats and rules for specific tasks, such as:
+  - [[HTTP]]/[[HTTPS]]
+  - [[FTP]], [[TFTP]]
+  - [[SMTP]], [[POP3]] , [[IMAP]]
+- Network infrastructure devices (routers, switches) don't care about Application-layer details.
+  - They just move messages across the network.
+  - Only the communicating hosts interpret the data