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Internet Control Message Protocol

Internet Control Message Protocol. ICMP. ICMP. ICMP has two major purposes: To report erroneous conditions To diagnose network problems. ICMP Message Format. Type. 1 byte. Which type of message?. Code. 1 byte. Which sub-type of message?. Checksum. 2 bytes.

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Internet Control Message Protocol

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  1. Internet Control Message Protocol ICMP

  2. ICMP • ICMP has two major purposes: • To report erroneous conditions • To diagnose network problems

  3. ICMP Message Format Type 1 byte Which type of message? Code 1 byte Which sub-type of message? Checksum 2 bytes Checksum of entire ICMP message Data ? Extra data (specific to the type of message)

  4. Important ICMP Messages • Echo Request/Reply • Destination Unreachable • Redirect • Time Exceeded • Parameter Problem • Router Advertisement/Discovery

  5. Echo Request/Reply • Echo Request (Type: 8, Code: 0): • Requests that the receiving host send a copy (echo) of the request back to the sender • Echo Response (Type: 0, Code: 0): • The response from the receiving host • Using these 2 commands is one way that the ping command can perform its function

  6. Destination Unreachable • Network Unreachable (Type: 3, Code: 0): • The network of the packet’s destination address field could not be reached • Network Unknown (Type: 3, Code: 6): • The network of the packet’s destination address field could not be located • Host Unreachable (Type: 3, Code: 1): • The host specified by the destination address could not be reached • Host Unknown (Type: 3, Code: 7): • The host specified by the destination address could not be located • Protocol Unreachable (Type: 3, Code: 2): • The specified protocol (e.g. TCP or UDP) could not be established with the specified host • Port Unreachable (Type: 3, Code: 3): • The specified port number could not be reached

  7. Redirect • Redirect (Type: 5, Code: 0): • This router knows of a better path to the specified destination • The next router in the new path is provided

  8. Time Exceeded • Time Exceeded (Type: 11, Code: 0): • The router has decremented the hop limit of a packet to zero and dropped the packet

  9. Parameter Problem • Parameter Problem (Type: 12, Code: 0): • Part of all of the packet’s IP header was invalid

  10. Router Advertisement/Discovery • Router Advertisement (Type: 9, Code: 0): • A router announces its existence using this type of message • Router Discovery (Type: 10, Code: 0): • A host explicitly searches for a router

  11. Ping ICMP Echo Request (Type: 8, Code: 0) Source Destination ICMP Echo Response (Type: 0, Code: 0)

  12. Traceroute Packet w/ Hop Limit = 1 ICMP Time Limit Exceeded Packet w/ Hop Limit = 2 ICMP Time Limit Exceeded Destination Source Router 1 Router 2 Router 3 Packet w/ Hop Limit = 3 ICMP Time Limit Exceeded Packet w/ Hop Limit = 4 Response to Packet

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