Please Whitelist This Site?

I know everyone hates ads. But please understand that I am providing premium content for free that takes hundreds of hours of time to research and write. I don't want to go to a pay-only model like some sites, but when more and more people block ads, I end up working for free. And I have a family to support, just like you. :)

If you like The TCP/IP Guide, please consider the download version. It's priced very economically and you can read all of it in a convenient format without ads.

If you want to use this site for free, I'd be grateful if you could add the site to the whitelist for Adblock. To do so, just open the Adblock menu and select "Disable on tcpipguide.com". Or go to the Tools menu and select "Adblock Plus Preferences...". Then click "Add Filter..." at the bottom, and add this string: "@@||tcpipguide.com^$document". Then just click OK.

Thanks for your understanding!

Sincerely, Charles Kozierok
Author and Publisher, The TCP/IP Guide


NOTE: Using software to mass-download the site degrades the server and is prohibited.
If you want to read The TCP/IP Guide offline, please consider licensing it. Thank you.

The Book is Here... and Now On Sale!

Read offline with no ads or diagram watermarks!
The TCP/IP Guide

Custom Search







Table Of Contents  The TCP/IP Guide
 9  TCP/IP Lower-Layer (Interface, Internet and Transport) Protocols (OSI Layers 2, 3 and 4)
      9  TCP/IP Internet Layer (OSI Network Layer) Protocols
           9  Internet Control Message Protocol (ICMP/ICMPv4 and ICMPv6)
                9  ICMP Concepts and General Operation

Previous Topic/Section
ICMP General Operation
Previous Page
Pages in Current Topic/Section
1
23
Next Page
ICMP Message Creation and Processing Conventions and Rules
Next Topic/Section

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 routing.

  • 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 functional pairs.

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.



Previous Topic/Section
ICMP General Operation
Previous Page
Pages in Current Topic/Section
1
23
Next Page
ICMP Message Creation and Processing Conventions and Rules
Next Topic/Section

If you find The TCP/IP Guide useful, please consider making a small Paypal donation to help the site, using one of the buttons below. You can also donate a custom amount using the far right button (not less than $1 please, or PayPal gets most/all of your money!) In lieu of a larger donation, you may wish to consider purchasing a download license of The TCP/IP Guide. Thanks for your support!
Donate $2
Donate $5
Donate $10
Donate $20
Donate $30
Donate: $



Home - Table Of Contents - Contact Us

The TCP/IP Guide (http://www.TCPIPGuide.com)
Version 3.0 - Version Date: September 20, 2005

© Copyright 2001-2005 Charles M. Kozierok. All Rights Reserved.
Not responsible for any loss resulting from the use of this site.