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!

Searchable, convenient, complete TCP/IP information.
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 Addressing

Previous Topic/Section
IPv6 Address Space Allocation
Previous Page
Pages in Current Topic/Section
123
4
5
Next Page
IPv6 Interface Identifiers and Physical Address Mapping
Next Topic/Section

IPv6 Global Unicast Address Format
(Page 4 of 5)

An Example Division of the Global Routing Prefix Into Levels

So, there is no longer any single structure for determining how the 48-bit routing prefix is divided in the global unicast hierarchy. As one example, it might be possible to divide it into three levels, as shown in Table 64, and diagrammed in Figure 97.


Table 64: Example IPv6 Unicast Routing Prefix Structure

Field Name

Size (bits)

Description

(Unicast Indicator)

3

Each unicast address starts with “001”; there is no official name for this (it used to be called the Format Prefix.

Level1 ID

10

Level 1 Identifier: The identifier of the highest level in the hierarchy. This would be used for assigning to the biggest Internet organizations the largest blocks of addresses in the global hierarchy. The number of Level 1 organizations would be 210 or 1,024.

Level2 ID

12

Level 2 Identifier: Each block assigned to a Level 1 organization would use 12 bits to create 4,096 address blocks to divide amongst the lower-level organizations it serves.

Level3 ID

23

Level 3 Identifier: Each Level 2 organization has 23 bits to use to divide its Level 2 address block. Thus, it could create over 8 million individual “/48” address blocks to assign to end user sites. Alternately, the 23 bits could be divided further into still lower levels to reflect the structure of the Level 2 organization's customers.



Figure 97: Example IPv6 Unicast Routing Prefix Structure

The top row shows the global IPv6 unicast address format. The second shows one example way to divide the Global Routing Prefix, into three levels using 10, 12 and 23 bits respectively. The third row shows how the first 10 bits are used to create 210 or 1,024 different Level1 blocks. The next row illustrates that for each of these 13-bit prefixes, we could have 212 or 4,096 Level2 blocks. Then, within each 25-bit Level2 ID, we have 23 bits or 8,388,608 Level3 blocks. At the bottom, a Level3 or “/48” would be assigned to an individual organization.

 


This is just one possible, theoretical way that the bits in a “/48” network address could be assigned. As you can see, with so many bits there is a lot of flexibility. In the scheme above we can have over 4 million level 2 organizations, each of which can assign 8 million /48 addresses. And each of those is equivalent in size to an IPv4 Class B address (over 65,000 hosts)!


Previous Topic/Section
IPv6 Address Space Allocation
Previous Page
Pages in Current Topic/Section
123
4
5
Next Page
IPv6 Interface Identifiers and Physical Address Mapping
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.