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While many ICMP messages are designed to be sent as error messages in response to packets of other protocols, some are designed to implement standalone functionality. For example, a type 3 ICMP message with a 0 code points to issues with the destination network, while a 1 code means that the issue is that the particular host is unreachable. For example, a type value of 3 means that the intended destination is unreachable.įor some types, there are multiple code values intended to provide additional information. Error data in ICMP is carried in two values: the type and the code.Īs shown above, the type of an ICMP packet contains the overall message that the message is intended to convey.
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ICMP in WiresharkĪs an error messaging protocol, the structure of an ICMP packet is designed to provide the necessary information to the recipient.
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As a result, an organization’s ICMP traffic should largely be confined inside the network boundary, but it is a common protocol to see in network traffic captures.
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