Huawei HCIA notes

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Network foundation

Layer 2 Ethernet protocol ： The encapsulation of ether

1. Remember two numbers ：4   18  ----->4 Parts of ,18 Bytes .

2. The goal is MAC 6 Bytes     Source MAC 6 byte    TYPE（ type ） 2 byte     FCS( check )2 byte  

MAC Address ：

1.24 Bit OUI+24 Bit custom

2. radio broadcast MAC ：FF-FF-FF-FF-FF-FF  ; unicast MAC   ： The lowest bit of the first byte     Set up 0   ; Multicast MAC  ： The lowest bit of the second byte Set up 1

The sending and receiving of data ：

1. Sending is a process of encapsulation ...

2. Receive a frame first check FCS, Read target MAC Address , See if it's your own , If so, receive , Look again TYPE What is the type , The decision is to leave it to the upper level agreement , If the goal is not your own drop.

Cables are commonly used 3 Kind of ：1. Coaxial cable   2. Twisted pair   3. Optical fiber

Broadcast domain and conflict domain ：

1. Broadcast domain refers to the range of broadcast frame transmission , The switch does not split the broadcast domain by default 、 The router divides the broadcast domain by default .

2. A shared media segment is in a conflict domain ,CSMA/CD Carrier sense multiple access technology with collision detection ------ It's not used now .

Duplex mode ：

1. Simplex -------- TV

2. Half duplex ------- Walkie-talkie ： Only one party initiates data at the same time .

3. full duplex ------- At any moment , Both sides can initiate data .

ARP agreement ：

1. The upper layer of Ethernet protocol is divided into ARP：0x0806

2. Application scenarios ---- Address resolution ： Use target IP Address to resolve the target MAC Address , If target IP Not in the same network with myself , Then the gateway is resolved MAC Address .

3. free ARP（ Without any reason ARP）: A new configuration IP After that, it will send out automatically ARP request , No reply is right .

4. When to launch ARP request ： When there is no local target MAC At the address , By the church ARP request .（ There is no local ARP When mapping table items ）