ICMP Protocol

---

Preface

Internet Control message protocol ICMP（Internet Cotrol Message Protocol） It's an important protocol in the network layer .ICMP The protocol is used to transmit all kinds of error and control information between network devices , It's for collecting all kinds of network information 、 It is very important to diagnose and eliminate all kinds of network faults . Using a ICMP Application time , Need to be right ICMP I am very familiar with the working principle of .

---

One 、ICMP The role of

• purpose
  • Gateway or target machine utilization ICMP Communicate with source
  • When something goes wrong , Provide feedback for reporting errors
• characteristic
  • Its control capability is not used to ensure the reliability of transmission
  • Itself is not reliable transmission
  • It is not used to reflect ICMP Message transmission
    

ping command

stay Windows Command line ping once , It's actually called ICMP agreement .

Two 、ICMP Data packets

Format

Type and code to identify different content

ICMP Redirect

ping Command cannot access parsing

ping The command is actually sending a string to the destination host , And ask it to echo .

• Unable to access the target network ,ICMP When packets are encapsulated downward ,MAC The address is gateway MAC Address , There is no target in the gateway IP The routing , The response comes from the gateway .
• Unable to access host , Of the same network segment IP, Direct use ARP request MAC Address , Can't get , Therefore, the data package cannot be encapsulated , The data packet cannot be sent out , The response comes from yourself .