# 計算機網路

## 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