TIL 20191208

1. network protocol: encapsulation

link layer switch	router
packet switch	packet switch
1~2 layer	1~3 layer

capsule을 씌워가며 메시지를 전송하면, ene-system(or packet switches)는 씌워진 캡슐을 벗겨 메시지를 해석하고, 필요하면 다시 자신의 캡슐을 씌워 전송한다.

2. DoS(denial or service) Attack

• vulnerability attack: host가 작동시키게 해서 동작을 멈추게 하는 등 악성 행동을 수행시킴.
• bandwidth flooding: flood fake packets, block normal packets
• DDoS: 공격자가 많은 숙주들을 감염시켜 둔 후, 한 host로 한 순간에 packet을 숙주들이 공격하게 지시함.
• connection flooding: flood fake TCP connection, block normal connection

3. packet sniffer(패킷 훔치기)

encryption으로 방지

4. IP spoofing(사칭하기)

end-point authentication이 필요!

5. History of computer networking

1. circuit switching -> packet switching develop
   ARPAnet(individual closed network) start
2. internetworking
   network of networks 개념 도입, TCP, UDP develop
   ALOHAnet develop: multiple access protocol
3. network 확산
4. internet bubble
   ARPAnet disappeared, WWW appear, web service flood
5. millenium
   content provider: made datacenter -> bypass ISP

6. Application layer (new chapter!)

• web app => server와 client 로 나뉨
  타 layer에 대한 제어 x
  
• application architecture != network architecture
• role of datacenter
  - bypass ISP
  • handle flooding requests
• application architecture
  1. server-client
  - server
  - always awake
  - has static address(IP)
  - client
  - init connection
  2. P2P architecture
     • few(or never) depend on server
       • host and host make peer
       • ex) file share, dowload accerlator, messangers
  3. hybrid
     • user server-client and p2p
       • ex) instant message application
• Process
  - host communicate not by program, but by process.
  two host communicate by exchange message.
  In this work, the door is socket and the house is process.
  socket: API between application and network
  • when sending packet, recieving process should have own address, and the packet should have two information - IP address, and port number.
    1. IP address: address of receiving host
    2. port number: recieving process of host.