[컴퓨터 네트워크] ICMP

Network Layer

ICMP

 

Internet Control Message

ICMP is used for communicating with hosts and router.

 

There are two types of usage.

• error report
• query message for dianosing network problems

 

Error report

 

• discard packet
  • destination is not in routing table
  • time exceeded; TTL is equal 1
  • source quench
  • parameter issue
• redirection

 

Content

 

• 8bytes is transport layer header
• IP header following ICMP header is datagram received by router

 

prior IP packet

• IP header + data(8bytes + rest)

add ICMP header

• ICMP header + IP header + data(8bytes + rest)

and then, add IP header

• IP header + ICMP header + IP header + data(8bytes + rest)

 

Query message

 

• echo request and reply; Ex> ping command
• etc..

 

ICMP type and code table

There are two application, ping and traceroute using ICMP packet.