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 Protocol (IP/IPv4, IPng/IPv6) and IP-Related Protocols (IP NAT, IPSec, Mobile IP)
                9  Internet Protocol Version 6 (IPv6) / IP Next Generation (IPng)
                     9  IPv6 Datagram Encapsulation and Formatting

Previous Topic/Section
IPv6 Datagram Main Header Format
Previous Page
Pages in Current Topic/Section
1
23456
Next Page
IPv6 Datagram Options
Next Topic/Section

IPv6 Datagram Extension Headers
(Page 1 of 6)

After the mandatory “main” header in an IPv6 datagram, one or more extension headers may appear before the encapsulated payload. These headers were created in an attempt to provide both flexibility and efficiency in the creation of IPv6 datagrams. All fields that are needed only for special purposes are put into extension headers and placed in the datagram when needed. This allows the size of the main datagram header to be made small and streamlined, containing only those fields that really must be present all the time.

There is often confusion regarding the role of extension headers, especially compared to datagram options. The IPv4 datagram had only one header, but it included a provision for options, and IPv6 also has options, so why bother with extension headers? Good question.

It would have been possible to do everything using options. However, it was deemed a better design to employ extension headers for certain sets of information that are needed for common functions such as fragmenting. Options are indeed still supported in IPv6; they are used to provide even more flexibility by providing variable-length fields that can be used for any purpose. They are themselves defined using extension headers as we will see below (and in their own topic, which follows.)

When extension headers are included in an IPv6 datagram, they appear one after the other following the main header. Each extension header type has its own internal structure of fields.


Previous Topic/Section
IPv6 Datagram Main Header Format
Previous Page
Pages in Current Topic/Section
1
23456
Next Page
IPv6 Datagram Options
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.