ICMP

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Internet Control Message Protocol:

Internet Control Message Protocol ICMP

ICMP:

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

ICMP Message Format:

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

Important ICMP Messages:

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

Echo Request/Reply:

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

Destination Unreachable:

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

Redirect:

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

Time Exceeded:

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

Parameter Problem:

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

Router Advertisement/Discovery:

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

Ping:

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

Traceroute:

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