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!

Enjoy The TCP/IP Guide? Get the complete PDF!
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 6 (ICMPv6) Error Message Types and Formats

Previous Topic/Section
ICMPv6 Destination Unreachable Messages
Previous Page
Pages in Current Topic/Section
12
3
Next Page
ICMPv6 Time Exceeded Messages
Next Topic/Section

ICMPv6 Packet Too Big Messages
(Page 3 of 3)

Applications of Packet Too Big Messages

While Packet Too Big is obviously an error message, it also has another use: the implementation of Path MTU Discovery. This process, described in RFC 1981, defines a method for a device to determine the minimum MTU for a path to a destination. To perform path MTU discovery, the source device sends a series of test messages, decreasing the size of the datagram until it no longer receives Packet Too Big messages back in response to its tests. See the topic on IPv6 MTU and fragmentation issues for a bit more detail on this.

Note: The Packet Too Big message is new to ICMPv6. However, its use is somewhat similar to the use of the Fragmentation Needed and DF Set version of the ICMP4 Destination Unreachable message type, which is used as part of IPv4’s path MTU discovery feature.


Incidentally, Packet Too Big is an exception to the rule that ICMP messages are sent only in response to unicast datagrams; it may be sent in reply to an oversized multicast datagram. If this occurs, it is important to realize that some of the intended targets of the multicast may still have received it, if the path the multicast took to them did not go through the link with the small MTU that caused the error.


Previous Topic/Section
ICMPv6 Destination Unreachable Messages
Previous Page
Pages in Current Topic/Section
12
3
Next Page
ICMPv6 Time Exceeded Messages
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.