Network Basic Knowledge

Network Basic Knowledge

switch connects to router connects to modem and modem connects to internet Home router combines modem and router switch controls LAN Router by default blocks communication of one LAN to another LAN LAN is identified by IP. (10.0.0.1, 10.0.0.2 => LAN1 vs 10.0.1.1, 10.0.1.2 => LAN 2) There are public IP address && private IP address(local) IP address can be static or dynamic static or dynamic is decided by devices' OS. Usually many OS chooses DHCP(Dynamic) IP by default. when a device connects to internet, it sends request to ask for dynamic IP, and dynamic IP us dispatched by DHCP server from ISP on in LAN, with an expiration date. Dynamic IP changes, but static does not Static IP usually assigned by network admin in LAN in private, or bought from ISP for public Router blocks all inbound connection requests by default(but if specified router virtual port # is mapped in the router's port forwarding table to a LAN Host and Port, router will use such LAN host and port's authentication), and allows all outbound connection by default. LAN host can establish websocket with vendor server outside. Any communication from LAN host to outside is achieved through router's public IP Switch has a flooding table to list LAN IP(dynamic or static) and their MAC address (can be configured by admin) Router has a port forwarding table to forward router virtual port to LAN host IP and port (can be configured by admin) LAN hosts, switches && routers are all servers actually. Router can be configured as a bridge so it loses routing capabilities, and act as a switch

There are 7 layers in OSI model

1. Physical layer (cable to use(transmit packet by light), or wifi(transmit package by radio wave) 2. data-link-layer (packet dest & src mac address is added, to deal with transmission errors, regulate the flow of data, and provide a well-defined interface to the network layer._ 3. Network Layer(Rout packets, this is where the IP address of src& dest of packet are added. * packet is just sequences of 0sand1s,except it contains information telling start of packet, content of packet, end of packet 4. Transport Layer decides which trasmission portocol to use to transfer packet(TCP/IP this is where packets src&dest port # are added) 5. Session Layer stores session (It establishes, manages, and terminates the connections between the local and remote application. It provides for full-duplex, half-duplex, or simplex operation, and establishes check-pointing, adjournment, termination, and restart procedures. ) 6. presentation layer (Data encryption/decryption) Character/string conversion Data compression Graphic handling ) 7. Application layer(. Manipulation of data(information) in various ways is done in this layer which enables user or software to get access to the network. HTTP, HTTPS, FTP, SSH, protocols are used in this layer. It can act as Network virtual terminal :- A network virtual terminal is a software version of a physical terminal, and it allows a user to log on to a remote host. File transfer, access, and management :- This application allows a user to access files in a remote host (to make changes or read data). Mail services :- This application provides the basis for e-mail forwarding and storage. Directory services :- This application provides distributed database sources and access for global information about various objects and services.