Interview_Network/Packetization/Protocol/OSI/TCPIP/Network Appliances

📌 Network

✅ What is computer network?

- connection of network devices to communicate data
- use WWW
- use HTTP

✅ What are the types of network?

- WAN
- LAN
- MAN
- PAN

✅ How can we transfer data on network?

- 회선 교환 방식: Circuit-Switched
- 👎🏻 when circuit is occupied, other computers cannot transmit data

- Packet Switched: Divide data into small packets and transmit
- 👍🏻 does not occupy circuit

✅ What is packetization?

- Packet: small segment of big data
- Packetization ➡️ Routing ➡️ Transmission medium ➡️ Reassembly ➡️ Error Checking

✅ What is protocol?

- Set of rules to transmit data on network
- for example, HTTP, SMTP, UDP

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📌 TCP/IP

✅ What is TCP/IP?

- Transmission Control Protocol, Internet Protocol

- Application Layer: show to user on application
- Transport Layer: data transmission, TCP/UDP
- Internet Layer: connect host, routing IP address
- Network Link Layer: transmit data through physical device

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📌 OSI 7 Layer

✅ What is OSI 7 layer?

- Application Layer: show to user on application [[HTTP/HTTPS]]
- Presentational Layer: change data format to transmitable format [[JPEG, ASCII]]
- Session Layer: connection between application, message, [[SSL/TLS]]
- Transport Layer: filter, manage traffic, segment, [[TCP/UDP]]
- Network Layer: different network, packet, [[IP address, Router, Ping]]
- Datalink Layer: same network, unit, MAC Address, [[Switch, Bridge]]
- Physical Layer: change 0, 1 to analog data, send to physical device, [[Hub, cable, repeater]]

✅ What are the benefits of dividing into layers?

- 👍🏻 can see how data is transfered
- 👍🏻 easier for debugging
- 👍🏻 compatible for any device
- 👍🏻 independent layers, dependency on other layers ⬇️

✅ Why is it called "layer"?

- header is added to data as it goes up/down the layers
- c(b(a))

✅ Why is header added as data goes up/down the layer?

- called encapsulation, decapsulation
- only the current layer can decapsulate until that layer level
- 👍🏻 reduce data latency(only open that layer header)
- 👍🏻 encrpyt, secure other layers

✅ Why is data trasmission always slower than excpected?

- bc header is added to data
- and needs time for encapsulation, decapsulation

✅ What is encapsulation and decapsulation?

- encapsulation: add header to data from higher layer ➡️ lower layer
- decapsulation: remove header from data from lower layer ➡️ higher layer

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📌 Network appliances

✅ What is NIC?

- Network Interface card
- OSI layer 1
- connect computer to network

✅ What is repeater?

- amplify digital signal for long distance travel
- OSI Layer 1(Physical Layer)

✅ What is hub?

- multi-port repeater
- one hub, one collision domain

✅ What is bridge?

- OSI Layer 2(data link layer)
- MAC address
- send unit based on MAC address
- has bridge table
- divides collision domain
- on same network

✅ What is L2 Switch?

- Like bridge, send unit to MAC address
- but has multiple ports
- OSI Layer 2(data link layer)
- on same network

✅ What is the difference between switch and bridge?

- switch has multiple ports compared to bridge

✅ What are the functions of switches and bridges

- learning
- flooding
- forwarding
- filtering
- aging
- aging reflash

✅ How does switch, bridge forward frame?

- store and forward
- cut-through
- fragment free

✅ What is looping

- when there is more than one way of reaching switch, hub
- other PCs cant send data
- 💊 Spanning Tree algorithm

✅ What is spanning tree algorithm?

- To prevent looping
- If more than one way of reaching switch, bridge, block all ways except one
- If problem occurs with current way, unlock the blocked way

✅ What is router?

- OSI Layer 3(network layer)
- IP address
- send packet based on IP address
- different network
- has routing table
- divide broadcast domain

✅ What is L3 Switch?

- switch ➕ router
- MAC address ➕ Routing table 🟰 FPGA hardware
- OSI Layer 3(Network Layer)

✅ What is L7 Switch?

- switch with load balancing, firewall, deep packet inspection
- forward data based on application data
- OSI Layer 7(Application Layer)

✅ What is load balancing?

- share work load to more than two servers

✅ What is gateway?

- passage to conenct two networks