計算機網路

參考自李春良老師 計算機網路課程部分PPT擷取
網路參考源: 國立台灣大學 Lecture Slides
Introduction to Computer Networks
Spring 2022

資安相關名詞

• botnet
• virus
• worm
• DDos
• IP spooting
• spyware
• packet sniffing (筆記手誤)

網路基本概念

• cookies
• IMAP v.s. POP3
• DNS(Domian name system)
• tracked, torrent
• DNS poisoning attack
• DNS provider
• web cache
• condition GET
• persistent HTTP

DNS的問題: 前身

假設一個DNS包含所有映射的DNS，會有四項問題

• 1. Single point of failure
• 2. Traffic volume
• 3. Distant centralized database
• 4. Maintenance

解決方法 ---> Hierarchical database(筆記手誤)

相關名詞

• Authoritire DNS Server
• Local DNS server

• recursive query
• iterative query

• DNS Caching

• DNS RR format

• Attack DNS
  • DDOS
  • bombard TLD Server

TCP觀念

• 1. reliable
• 2. flow control
• 3. congestion control
• 4. In transport layer

SSL加密

• 1. provide TCP encrypted connection
• 2. In application layer

SMTP(Simple Mail Transfer protocol)

• 1. hand shaking
• 2. transfer msg
• 3. closure

Transport & Network layer

• UDP
• TCP

• Go back-N

• Select repeat

TCP

TCP segment structure

TCP retransmission scenarios

• 1. Lost ACK
• 2. Premature timeout
• 3. Commulative ACK

• TCP fast retransmit

• Three-way handshake

• Congestion Control
• 1. AIMD --> Slow start問題

• TCP fair

• forwarding
• routing

• Data plane
• Control plane

• Longest prefix matching(LPM)

網路連結方式

1. Switch
2. Bus
3. Crossbar

HOL (Hand of the line blocking)問題與排排程機制

• 問題

• 解法
• 1. FIFO
• 2. Priority
• 3. RR
• 4. WFQ(Weighted Fair Queing)

ICMP protocol

• network link layer

IP Addressing 方法

*　Subnet Group

• CIDR

• IP 取得方式
• 1. 手動
• 2. 自動(DHCP)

NAT(Networling Addressing Translation)

Routing ALGO分類

1. 根據router知道全域 & 區域資料
   • Global: Link State ALGO
     • Broadcast產生Forwading Table
     • Dijkastra's algo
     • 缺點(特色): 容易震盪(Oscillation Possible)
   • Decentralized: Distance vector algo
     • 鄰近節點找最短路徑
     • Bellman Ford algo
     • 缺點(特色): Bad news travels slow(count to infinity問題)
2. 根據更新速度
   • Static
   • Dynamic
     

• 兩種協定比較

Internet approach

• 1. Intra AS (AS 內部)
  • 1. RIP(Routing Information Protocol)
  • 2. OSPF(Open Shortest Path First)
  • 3. IGRP(Interier Gateway Routing Protocol)
• 2. Inter AS (AS 間): 只有 BGP(Border Gateway Protocol)
  • eBGP(egress)
  • iBGP(ingress)

• OSPF

• ICMP

• SNMP

Link layer

• Link
  • 1. wired link
  • 2. wireless
  • 3. LANS

• Link layer serice
  • flow control
  • error detection
  • error correction
  • half-duplex, full-duplex

• Error Detection
  • 1. Parity checking(Odd/Even)
  • 2. CRC(Cyclic Redundancy Check)

Multuple Access & MAC

Multiple Access	Protocol 理想四要件判斷

• MAC Protocol分類
  • 1. Channel Partitioning(筆記手誤)
    • TDMA(Time Division Multiple Access)
    • FDMA(Frequency Division Multiple Access)
  • 2. Random Access
    • Slotted ALOHA
    • Pure(unslotted) ALOHA
    • CSMA(Carrier Sense Multiple Access)
    • CSMA/CD
    • CSMA/CA
  3. Taking turns
     

ARP

Ethernet