Title
Message Types
Uses
References
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There are 8 major messages that the ICMP standard sets up: Echo and Echo Reply,
Destination Unreachable, Source Quench, Redirect, Time Exceeded, Parameter Problem,
Timestamp, Address Mask Request and Reply.
| Destination Unreachable | Destination Unreachable Message happens if
the destination of the datagram is unreachable or if the protocol module or process port
is not active or if a datagram needs to be fragmented to go through a gateway and there
is a Don’t Fragment flag on the packet.
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| Time Exceeded | Time Exceeded Message is sent when the time to live field is zero or if
a host cannot complete the defragmentation process for a fragmented datagram due to missing
fragments within its specified time.
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| Parameter Problem | Parameter Problem Message occurs when the header parameters
have some type of error such that the host or gateway cannot properly process the
datagram.
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| Source Quench | A Source Quench message is a request to the hot to slow down the rate at
which it is sending packets to the internet destination because the gateway is getting or is
overloaded.
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| Redirect | A Redirect message is sent when a gateway realizes that the datagram
it received would be sent quicker if it were sent directly to the destination rather through
that gateway.
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| Echo and Echo Reply | Echo message sends a reply and expects an Echo reply with
the original message encapsulated in it.
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| Timestamp | The Timestamp can be one of three timestamps. The first time stamp is the last time the
sender had the message before sending it. The second time stamp is when the echoer first
took in the message. Finally the last is the time right before the echoer sent the
message.
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| Informational Request | The Informational Request is how a host discovers
which network it is on by having the message sent with the source network in the IP header
source.
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These messages allow the network to communicate with one another about important matters such as timing, errors and other problems within the network or the packets sent. This messaging is extremely important otherwise there would be no communication between any of the nodes on the network.
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