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 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 Overview and General Structure
Previous Page
Pages in Current Topic/Section
12
3
Next Page
IPv6 Datagram Extension Headers
Next Topic/Section

IPv6 Datagram Main Header Format
(Page 3 of 3)

Key Changes to Main Header Between IPv4 and IPv6

To summarize, the IPv6 main header compares to the IPv4 header as follows:

  • Unchanged Fields: Three fields are used the same way and retain the same name (though they have different content and/or size): Version, Source Address and Destination Address.

  • Renamed Fields: Two fields are used the same way but renamed: Traffic Class and Hop Limit.

  • Modified Fields: Two fields are used in a way similar way to their IPv4 predecessors but are slightly different in meaning and also renamed: Payload Length and Next Header.

  • Added Fields: There is one new field: Flow Label.

  • Removed Fields: To cut down on header length and unnecessary work, five IPv4 header fields are removed from the IPv6 header:
    • Internet Header Length: No longer needed, as the main IPv6 header is fixed in length at 40 bytes.

    • Identification, Flags, Fragment Offset: These are used for fragmentation, which is done less in IPv6 than IPv4, so these fields are now found only when needed in the Fragmentation extension header.

    • Header Checksum: The decision was made to eliminate header checksum calculations in IPv6. It was viewed as redundant with higher-layer error-checking and data link layer CRC calculations. This saves processing time for routers and 2 bytes in the datagram header.

In addition, while options were formerly considered part of the main header in IPv4, they are separate in IPv6.


Previous Topic/Section
IPv6 Datagram Overview and General Structure
Previous Page
Pages in Current Topic/Section
12
3
Next Page
IPv6 Datagram Extension Headers
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.