Transcript Internet Control Message Protocol

Internet Control Message
Protocol
ICMP
ICMP
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ICMP has two major purposes:
– To report erroneous conditions
– To diagnose network problems
ICMP Message Format
1 byte
Type
Which type of message?
1 byte
Code
Which sub-type of message?
2 bytes
Checksum
?
Data
Checksum of entire ICMP message
Extra data (specific to the type of message)
Important ICMP Messages
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Echo Request/Reply
Destination Unreachable
Redirect
Time Exceeded
Parameter Problem
Router Advertisement/Discovery
Echo Request/Reply
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Echo Request (Type: 8, Code: 0):
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Echo Response (Type: 0, Code: 0):
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Requests that the receiving host send a copy
(echo) of the request back to the sender
The response from the receiving host
Using these 2 commands is one way that
the ping command can perform its function
Destination Unreachable
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Network Unreachable (Type: 3, Code: 0):
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The network of the packet’s destination address field could not be reached
Network Unknown (Type: 3, Code: 6):
–
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The network of the packet’s destination address field could not be located
Host Unreachable (Type: 3, Code: 1):
–
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The host specified by the destination address could not be reached
Host Unknown (Type: 3, Code: 7):
–
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The host specified by the destination address could not be located
Protocol Unreachable (Type: 3, Code: 2):
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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
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Redirect (Type: 5, Code: 0):
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This router knows of a better path to the
specified destination
The next router in the new path is provided
Time Exceeded
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Time Exceeded (Type: 11, Code: 0):
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The router has decremented the hop limit of a
packet to zero and dropped the packet
Parameter Problem
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Parameter Problem (Type: 12, Code: 0):
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Part of all of the packet’s IP header was invalid
Router Advertisement/Discovery
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Router Advertisement (Type: 9, Code: 0):
–
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A router announces its existence using this type
of message
Router Discovery (Type: 10, Code: 0):
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A host explicitly searches for a router
Ping
ICMP Echo Response (Type: 0, Code: 0)
Destination
Source
ICMP Echo Request (Type: 8, Code: 0)
Traceroute
Packet w/ Hop Limit = 1
ICMP Time Limit Exceeded
Packet w/ Hop Limit = 2
ICMP Time Limit Exceeded
Destination
Packet w/ Hop Limit = 3
Router 3
Router 2
Router 1
Source
ICMP Time Limit Exceeded
Packet w/ Hop Limit = 4
Response to Packet