The TCP/IP Guide - ICMPv6 Packet Too Big Messages

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

**Table 104: ICMPv6 *Packet Too Big* Message Format**
Field Name	Size (bytes)	Description
*Type*	1	*Type:* Identifies the ICMPv6 message type; for Packet Too Big messages this is set to 2.
*Code*	1	*Code:* Not used for this message type; set to 0.
*Checksum*	2	*Checksum:* 16-bit checksum field for the ICMP header, as described in the topic on the ICMP common message format.
*MTU*	4	*MTU:* The maximum transmission unit (MTU) size, in bytes, of the physical link over which the router wanted to send the datagram, but was not able to do so due to the datagram's size. Including this value in the Packet Too Big message tells the source device the size it needs to use for its next transmission to this destination to avoid this problem in the future (at least for this particular link.)
*Original Datagram Portion*	Variable	*Original Datagram Portion:* As much of the IPv6 datagram as will fit without causing the size of the ICMPv6 message (including its own IP header) to exceed the minimum IPv6 MTU of 1280 bytes.