Network planning | [four network layers] knowledge points and examples

 

One 、 Knowledge point

 

1、SDN Three levels of controller

 2、 Network layer functions

In the structure of multiple LANs interconnected by routers , Each LAN physical layer is required 、 Data link layer 、 Network layer protocols can be different , The high layer protocols above the network layer must be the same .

3、 Agreements at all levels

4、1 Multiple hosts IP Address , But it must belong to multiple logical networks .

5、

6、 IP Related agreements / operation

7、ICMP

 

 8、IPv6 Fundamentally solve the problem of address exhaustion

Improved header format , Rapid processing / Forward datagrams , Support QoS.

QoS (Quality ofService, Service quality ) It means that a network can utilize various basic technologies , Provide better service capability for specified network communication , It's a kind of network security mechanism , It's a technology to solve the problems of network delay and blocking . When the network is overloaded ,QoS It can ensure that important traffic is not delayed or discarded , At the same time to ensure the efficient operation of the network . 

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Two 、 Example

 

Don't consider NAT, stay Internet in ,lP Datagrams may need to go through multiple networks and routers from the source node to the destination node , Throughout the transmission ,IP In the datagram header （）

A. Neither the source address nor the destination address will change

B. The source address may change but the destination address will not

C. The source address will not change, but the destination address may change

D. Both the source address and the destination address may change

Analysis of the answer ：

IP Datagrams are in transit , The source and destination addresses do not change , What will change is MAC Address , Even if IP Newspaper and quilt segmentation , The source address and destination address will also be copied to the new partition . So choose A.

Don't think about NAT Under the circumstances , Source / Purpose IP The address will not change , Source / Purpose MAC The address will change

In considering NAT Under the circumstances , Source / Purpose Intranet IP The address will change , Source / Purpose MAC The address will change

 1、 Don't consider NAT , IP The address will not change

 2、 consider NAT , Intranet IP The address will change

 3、 Just go through the router , MAC The address has changed

 

The subnet mask of a subnet is 255.255.255.224 , - A total of four hosts are assigned IP Address , One of them is due to IP Improper address assignment and communication failure . The of this host IP The address is ()

A .202.3.1.33

B .202.3.1.65

C .202.3.1.44

D .202.3.1.55

 

  Suppose a NAT The public network address of the router is 205.56.79.35, And there are the following table items :

It receives a source IP The address is 192.168.32.56、 The source port is 80 The grouping , The action is ( ).

A. Change address , Will source IP Turn into 205.56.79.35, The port changes to 2056, Then send it to the public network

B. Add a new entry , transformation IP The address and port are then sent to the public network

C. Do not forward , Discard the packet

D. Forward packets directly to the public network

 

  A correct example ：

Adding a new table entry is the job of an administrator .