What is ICMP? What is the relationship between Ping and ICMP?

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Today, at the request of fans, let's talk about ICMP, Speaking of ICMP, What do you think , Familiar with , But when you think about it, you can't say anything , So this is the purpose of this article .

Let's go straight to ！

What is? ICMP？

• English full name ：
  Internet Control Message Protocol

• Chinese name ：
  Internet control message protocol

• Working in  OSI  Model
  The network layer
  and  TCP/IP  Model  
  Internet  layer

• ICMP  Messages are not delivered directly to the data link layer

• stay  RFC 792  In the definition of

ICMP  It is not usually used directly by user applications on the network , And with  TCP  and  UDP  It works in a completely different way .

In short ,ICMP  The main purpose of is to send  Echo ICMP  Asking for information  Ping  or  Trace  Tools , To calculate and determine whether computers on the network are available 、 The time it takes packets to and from this computer and the number of computers they pass through .

ICMP history

ICMP  Belong to  TCP/IP  Protocol stack , One of the pioneers of the Internet  Jon Postel  Write the  ICMP  The original concept of ,1981  year  4  month , stay  RFC 777  in , Prepared the first standard ,RFC 792  Also by  Postel  Written and published on  1981  year  9  Month by month  Internet Engineering Community  released .

ICMP  Structure

• type Type：ICMP  Each message in contains a unique type and is placed in this field , One of the common fields is called  echo request, The type is  8, This field is  8  position , So there is  256  Message types .

• Code Code：ICMP  For each type of message, a Code Additional information about the field , The code field is  8  position , Yes  256  Possible values .

• The checksum Checksum： That field is  16  position , The calculation method is the same as  IPv4  similar , For the whole  ICMP  Messages provide error detection of messages .

ICMP The function of

ICMP  A device mainly designed to work in a path connecting a transmitting device to a receiving device , The most common device that works in the middle of a path is a router ,ICMP  Not limited to routers , Any device in the network can use  ICMP  And send a message to another device ,ICMP  Provide a single mechanism for all control and information messages .

ICMP The main functions are as follows .

• When the source sends  IP  When a packet cannot be delivered , Allow the router to notify the source .

• Allow the source to discover all available paths to the target device .

• Allows the source to check whether the target device is online and up .

• Allow administrators to test connections and debug connection related issues .

ICMP  news

ICMP The main news is as follows ：

Echo Request / Echo Reply

• Chinese name ： Echo request / Echo response

• Echo Reply：ICMP Type 0

• Echo Request：ICMP Type 8

Echo messages can be used to determine whether devices on the network are working .

The local computer sends... To the target computer  ICMP Echo Request  news , The receiving computer uses  Echo Replymessage  To respond .

Destination Unreachable

• Chinese name ： Destination unreachable

• ICMP Type 3

Indicates that the destination network cannot be reached 、 Host or port

Redirect

• Chinese name ： Redirect

• ICMP Type 5

Used to redirect the host to a different network path .

Source Quench

• Chinese name ： Source inhibition

• ICMP type 4

Used to implement a basic flow control mechanism , And notify the source to stop sending packets for a period of time .

This message informs datagram packets to be transmitted quickly over the network , If resources are busy , Then the packet transmission speed to the source device is slowed down .

Time Exceeded

• Chinese name ： The supermarket

• ICMP Type 11

Indicates that there are too many hops , Has exceeded its lifetime  ( TTL ).

Message type summary ：

summary

Internet  Control message protocol  (ICMP)  yes  TCP/IP  Practical protocols for , Responsible for providing relevant information  TCP/IP  Devices on the network 、 Information about the availability of services or routes , Most network troubleshooting techniques and tools are based on common  ICMP  The message type is central , The most famous is ping, It is mainly used for communication between test equipment .