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!

The whole site in one document for easy reference!
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
12
3
Next Page
ICMP Message Creation and Processing Conventions and Rules
Next Topic/Section

ICMP Message Classes, Types and Codes
(Page 3 of 3)

ICMP Message Class and Type Summary

A complete section describing all of the major ICMP message types for both ICMPv4 and ICMPv6 has been included in this Guide. For convenience, I have summarized all these message types in Table 86, which shows each of the Type values for the messages covered in this Guide, the name of each message, a very brief summary of its purpose, and the RFC that defines it. (To keep the table from being egregiously large I have not shown each of the Code values for each Type value; these can be found in the individual message type descriptions.) The table is organized into sections in the same way as the ICMP Message Types and Formats section, except this table is sorted by ascending Type value within each category, for easier reference.


Table 86: ICMP Message Classes, Types and Codes

Message Class

Type Value

Message Name

Summary Description of Message Type

Defining RFC Number

ICMPv4 Error Messages

3

Destination Unreachable

Indicates that a datagram could not be delivered to its destination. The Code value provides more information on the nature of the error.

792

4

Source Quench

Lets a congested IP device tell a device that is sending it datagrams to slow down the rate at which it is sending them.

792

5

Redirect

Allows a router to inform a host of a better route to use for sending datagrams.

792

11

Time Exceeded

Sent when a datagram has been discarded prior to delivery due to expiration of its Time To Live field.

792

12

Parameter Problem

Indicates a miscellaneous problem (specified by the Code value) in delivering a datagram.

792

ICMPv4 Informational Messages
(part 1 of 2)

0

Echo Reply

Sent in reply to an Echo (Request) message; used for testing connectivity.

792

8

Echo (Request)

Sent by a device to test connectivity to another device on the internetwork. The word “Request” sometimes appears in the message name.

792

9

Router Advertisement

Used by routers to tell hosts of their existence and capabilities.

1256

10

Router Solicitation

Used by hosts to prompt any listening routers to send a Router Advertisement.

1256

13

Timestamp (Request)

Sent by a device to request that another send it a timestamp value for propagation time calculation and clock synchronization. The word “Request” sometimes appear in the message name.

792

14

Timestamp Reply

Sent in response to a Timestamp (Request) to provide time calculation and clock synchronization information.

792

15

Information Request

Originally used to request configuration information from another device. Now obsolete.

792

ICMPv4 Informational Messages
(part 2 of 2)

16

Information Reply

Originally used to provide configuration information in response to an Information Request message. Now obsolete.

792

17

Address Mask Request

Used to request that a device send a subnet mask.

950

18

Address Mask Reply

Contains a subnet mask sent in reply to an Address Mask Request.

950

30

Traceroute

Used to implement the experimental “enhanced” traceroute utility.

1393

ICMPv6 Error Messages

1

Destination Unreachable

Indicates that a datagram could not be delivered to its destination. Code value provides more information on the nature of the error.

2463

2

Packet Too Big

Sent when a datagram cannot be forwarded because it is too big for the maximum transmission unit (MTU) of the next hop in the route. This message is needed in IPv6 and not IPv4 because in IPv4, routers can fragment oversized messages, while in IPv6 they cannot.

2463

3

Time Exceeded

Sent when a datagram has been discarded prior to delivery due to the Hop Limit field being reduced to zero.

2463

4

Parameter Problem

Indicates a miscellaneous problem (specified by the Code value) in delivering a datagram.

2463

ICMPv6 Informational Messages

128

Echo Request

Sent by a device to test connectivity to another device on the internetwork.

2463

129

Echo Reply

Sent in reply to an Echo (Request) message; used for testing connectivity.

2463

133

Router Solicitation

Prompts a router to send a Router Advertisement.

2461

134

Router Advertisement

Sent by routers to tell hosts on the local network the router exists and describe its capabilities.

2461

135

Neighbor Solicitation

Sent by a device to request the layer two address of another device while providing its own as well.

2461

136

Neighbor Advertisement

Provides information about a host to other devices on the network.

2461

137

Redirect

Redirects transmissions from a host to either an immediate neighbor on the network or a router.

2461

138

Router Renumbering

Conveys renumbering information for router renumbering.

2894


You can see that several of the message types are quite similar in ICMPv4 and ICMPv6, but there are some slight differences. An obvious one is that Redirect is considered an error message in ICMPv4, but an informational message in ICMPv6. The way that the messages is used also often different. In IPv6, the use of many of the ICMP informational messages is described in the Neighbor Discovery (ND) protocol, which is new to IPv6.

Note that the Information Request and Information Reply messages were originally created to allow devices to determine an IP address and possibly other configuration information. This function was later implemented using protocols such as RARP, BOOTP and DHCP, and these message types obsoleted.


Previous Topic/Section
ICMP General Operation
Previous Page
Pages in Current Topic/Section
12
3
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.