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ISO OSI model, Why DNS and DHCP are UDPs?, What is ARP broadcast? what is…

- - - - sends bits of data
    - - This layer defines format of header and trailer for both parties to send and receive data.
      - Protocols: Ethernet (MAC address), PPP, WAP, ARP (IP to MAC)
      - Frame
        
        Encapsulate all data above
        
        Header
        
        Encapsulates user source and destination MAC address
        
        Trailer
        
        FCS (Frame Check Sequence) - uses to verify there were no transmission error
    - - IP addresses and networking
        
        Logical Addressing (Routed) - defines how each device can have an IP address
        
        Forwarding (Routing) defines how devices (router switches) forward packets to their final destinations.
        Also refers to finding best routes (tracer) for a packet to get to its destination
      - Protocols
        
        ROUTED: IP (IPv4, IPv6), ICMP (ping)
        
        ROUTING: Protocols BETWEEN routers (EIGRP, OSPF, RIPv2, BGP). These protocols goal is to find best routes from machine to machine
        
        IPsec, IGMP
      - encapsulation header: Packet
    - - Defines protocols that are related to data delivery to other computer (host to host)
      - for e.g. error recovery
      - flow control, regulate amount of data passing from comp to comp, windowing
      - 3 way handshake
      - Protocols: TCP (reliable), UDP (not reliable)
      - Devices: Firewalls, Hosts
      - Source (lol source can have port too) and Destination Port Info
      - encapsulation header: Segment
    - - Application layer is for communication protocols. It is for applications communication.
      - Protocols: HTTP, DNS, SSH, TELNET
    - - 1 Application: Pure Data
        
        2 Transport: Data with Transport info (Segment)
        
        3 Network: Segment with Network info (Packet)
        
        4 Data - Link: Packet with Data Link info (Header, Frame) (Frame)
        
        uses: S D MAC address Trailer (FSC 4 bytes)
        
        uses: S D IP
        
        uses: S D port (Source Destination)
  - - - maps MAC to IP and stores it in ARP tables
      - ARP Broadcast - used to find devices on a network that are not listed in the ARP table
        
        It screams to all devices through switch and has ARP FFFF FFFF FFFF. our source seeks address 192.168.1.20. And then all devices in the network get the packet. Then the destination sends to source its MAC address for source to add to ARP table
  - - - Layer 3 Packet [H][Segment]
        
        Layer 2 Frame [H][Packet][T] ( T - Trailer FCS, can be called CRC )
    - - router rips off mac address and substitute its MAC with destination device MAC address using only IP address info to do it
- - - - Defines and negotiates data formats such as ASCII, binary, JPEG. Encryption is a presentation layer service
    - - Defines how to start control and end sessions, Includes control management of messages. Has a seamless view of the data stream
    - - Provides data delivery, error recovery and flow control
    - - Defines addressing, forwarding and path determination
    - - Defines rules that determine when a device can send data over a particular medium
    - - Refers to standards that deal with the physical characteristics of physical data transmission.
    - - Provides interface for communication between two parties