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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

IPv6 Addressing 1 2 IPv6 Address Size and Address Space

In the IPv6 overview section I explained that IPv6 represents a significant update to the Internet Protocol, but that its modifications and additions are made without changing the core nature of how IP works. Addressing is the place where most of the differences between IPv4 and IPv6 are seen, but the changes are mostly in how addresses are implemented and used. The overall model used for IP addressing in IPv6 is pretty much the same as it was in IPv4; some aspects have not changed at all, while others have changed only slightly.

Some of the general characteristics of the IPv6 addressing model that are basically the same as in IPv4:

• Core Functions of Addressing: The two main functions of addressing are still network interface identification and routing. Routing is facilitated through the structure of addresses on the internetwork.
  
  
• Network Layer Addressing: IPv6 addresses are still the ones associated with the network layer in TCP/IP networks, and are distinct from data link layer (also sometimes called physical) addresses.
  
  
• Number of IP Addresses Per Device: Addresses are still assigned to network interfaces, so a regular host like a PC will usually have one (unicast) address, and routers will have more than one, for each of the physical networks to which it connects.
  
  
• Address Interpretation and Prefix Representation: IPv6 addresses are like classless IPv4 addresses in that they are interpreted as having a network identifier part and a host identifier part, but that the delineation is not encoded into the address itself. A prefix length number, using CIDR-like notation, is used to indicate the length of the network ID (prefix length).
  
  
• Private and Public Addresses: Both types of addresses exist in IPv6, though they are defined and used somewhat differently.

IPv6 Addressing 1 2 IPv6 Address Size and Address Space