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!

Get The TCP/IP Guide for your own computer.
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 Message Types and Formats
                     9  ICMP Version 4 (ICMPv4) Error Message Types and Formats

Previous Topic/Section
ICMPv4 Redirect Messages
Previous Page
Pages in Current Topic/Section
1
2
Next Page
ICMP Version 4 (ICMPv4) Informational Message Types and Formats
Next Topic/Section

ICMPv4 Parameter Problem Messages
(Page 2 of 2)

Parameter Problem Message Interpretation Codes and The Pointer Field

When a Parameter Problem message is generated due to a specific bad field in the original message, the Pointer field is used as described above to show the location of the problem. This meaning of the Parameter Problem message is the one that was defined in the original ICMP standard, RFC 792, and is associated with Code value 0. There are some cases of a parameter problem where a pointer to a specific field in the original message really wouldn't make sense, so other standards have defined two new Code field values for Parameter Problem messages. Table 95 shows the three Code values and provides a brief explanation of each.


Table 95: ICMPv4 Parameter Problem Message Interpretation Codes

Code Value

Message Subtype

Description

0

Pointer Indicates The Error

This is the normal use of the Parameter Problem message; when this Code value is used, the Pointer field indicates the location of the problem.

1

Missing A Required Option

The IP datagram needed to have an option in it that was missing. Since the option was missing there is no way to point to it, of course. J

2

Bad Length

The length of the datagram overall was incorrect, indicating a general problem with the message as a whole. Again, the Pointer field makes no sense here.


Key Concept: The ICMPv4 Parameter Problem message is a generic “catch all” that can be used to convey an error of any type in an IP datagram. A special Pointer field is normally used to indicate to the recipient of the message where the problem was in the original datagram.


Note that the Pointer field is only 8 bits wide, but since this allows for values up to 256 this is sufficient to allow it to point to any location within the IP header. It is possible for the Pointer field to point to a field within an IP option. Both hosts and routers can generate Parameter Problem messages.

 


Previous Topic/Section
ICMPv4 Redirect Messages
Previous Page
Pages in Current Topic/Section
1
2
Next Page
ICMP Version 4 (ICMPv4) Informational Message Types and Formats
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.