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ICMP Message Classes, Types and Codes
(Page 1 of 3)
ICMP messages are used to allow the
communication of different types of information between IP devices on
an internetwork. The messages themselves are used for a wide variety
of purposes, and are organized into general categories, as well as numerous
specific types and subtypes.
ICMP Message Classes
At the highest level, ICMP messages
are divided into two classes:
- Error Messages: These messages are used
to provide feedback to a source device about an error that has occurred.
They are usually generated specifically in response to some sort of
action, usually the transmission of a datagram, as shown in the example
of Figure 137.
Errors are usually related to the structure or content of a datagram,
or to problem situations on the internetwork encountered during datagram
- Informational (or Query) Messages: These
are messages that are used to let devices exchange information, implement
certain IP-related features, and perform testing. They do not indicate
errors and are typically not sent in response to a regular datagram
transmission. They are generated either when directed by an application,
or on a regular basis to provide information to other devices. An informational
ICMP message may also be sent in reply to another informational ICMP
message, since they often occur in request/reply or solicitation/advertisement
Key Concept: ICMP messages are divided into two general categories: error messages that are used to report problem conditions, and informational messages that are used for diagnostics, testing and other purposes.
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Version 3.0 - Version Date: September 20, 2005
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