Huawei HCIA notes

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Network foundation

Three layers IP agreement ：IP The packaging of the head

1. Grow long ,20-60 Bytes get longer .

2. Version edition   V4 or V6.

3. Total Length IP The total size of the bag .

4. TTL：1. Data level anti ring mechanism .2. Every time you pass through a router , Will be reduced 1, When reduced to 0 When , this IP The message will be drop.

5. Protocol  ： Distinguish the upper layer protocol ,6 It means that the upper layer is TCP,17 It means that the upper layer is UDP.

6. S/D IP   ： Source / Objective   IP  , Where is it from , Where to go? .

IP Address ： Basic knowledge

1. The length is 32 position , Dot decimal is used to express .

2. Network bit is to find the corresponding network first , Then find the host to be determined in this network .

3. A zero host indicates the network itself , network number 、 Prefix 、 route .192.168.1.0/24

4. Host location is fully set 1, Can represent all hosts on this network . Subnet broadcast .

IP classification ：A class ：

1. The highest bit of the first byte must be set to 0,0-127

2.  1-126

3. The first byte is the network bit , The last three bytes are the host bit .

B class ：

1. The top two bits of the first byte must be set to 10,128-192.

2.  128-191

3. The first two bytes are network bits , The last two bytes are the host bit .

C class ：

1. The highest three bits of the first byte must be set to 110,

2. 192-223

3. front 3 Bytes are network bits , The last byte is the host bit .

private IP：

A class ：10.0.0.0/8

B class ：172.16.0.0/16-172.31.0.0/16

C class ：192.168.0.0/24-192.168.255.0/24

Special address ：

Local return address ：127.0.0.0 - 127.255.255.255

No address specified （ For filling ）     0.0.0.0

Broadcast address      255.255.255.255

Subnet mask ：

1. effect ：32 position , And IP Address 11 corresponds to , modification IP There's no point in having a mask for the address alone .

2.  1 The corresponding IP The address part is the network bit .

3.  0 The corresponding IP The address part is the host location .

4.  Two expressions ： dotted decimal   /  CIDR

Subnet partition ：

1. The core idea ： Borrow the host location , Expand network bits . To get more subnets .

2. effect ： Distribute it rationally IP Address .

3. Method 1： Depending on the number of subnets needed , Determine the number of subnets .

  Method 2： Depending on the number of hosts needed , Determine the number of hosts , Then determine the number of subnets .

4. Block size method ：

1. Determine the number of subnet partitions that occur 8 Bit group .

2. Make sure that 8 Bit block size .

3. Add up according to the size of this block .

4. Determine block size =2^n,N= Number of hosts .256 Subtract the 8 Bit mask .

ICMP agreement ：

1.  ICMP Packaged in IP Inside , The agreement number is 1.

2. Connectivity testing -----ping  、echo request  、echo reply  ; TYPE 0/8

3. Redirect ： Solve the problem of suboptimal host path . 

4. Tracert ： Explore the path you're going through .

Layers of agreement ：

1. In terms of encapsulation, it's hierarchical .

2. According to the object of service （ The main ）