Internet Routing Architectures (CISCO):Handling IP Address Depletion



























Previous
Table of Contents
Next




IP Version 6 (IPv6)
IP version 6 (IPv6), also known as IP next generation (IPng), is a move to improve the existing IPv4 implementation.

The IPng proposal was released in July 1992 at the Boston Internet Engineering Task Force (IETF) meeting, and a number of working groups were formed in response. IPv6 tackles issues such as the IP address depletion problem, quality of service capabilities, address autoconfiguration, authentication, and security capabilities.
IPv6 is still in its experimentation stage. It is not easy for companies and administrators deeply invested in the IPv4 architecture to migrate to a totally new architecture. As long as the IPv4 implementation keeps providing hooks and techniques (as cumbersome as they might be) to tackle all the major issues that IPv6 will solve, adopting IPv6 might not seem very compelling to many companies. How soon or how late people will migrate to IPv6 is yet to be seen.
As far as this book is concerned, we will only touch on part of the IPv6 addressing scheme and how it compares to what you already have seen in IPv4.
The IPv6 addresses are 128 bits long (compared to 32 bits in IPv4). This should provide ample address space to handle scalability issues in the Internet (128 bits of addressing will translate into 2128—which is a lot of addresses).
The types of IPv6 addresses are indicated by the leftmost bits of the address in a variable length field called the Format Prefix (FP). This is illustrated in figure 3-21.

Figure 3-21  IPv6 prefix and address format.
Table 3-4 outlines the initial allocation of these prefixes. IPv6 has defined multiple types of addresses; we are interested in the provider-based unicast addresses and the local use addresses for comparison with IPv4 techniques.


Table 3-4 Allocation of IPv6 prefixes.



Description
Format Prefix



Reserved
0000 0000

Unassigned
0000 0001

Reserved for NSAP Allocation
0000 001

Reserved for IPX Allocation
0000 010

Unassigned
0000 011

Unassigned
0000 1

Unassigned
0001

Unassigned
001

Provider-Based Unicast Address
010

Unassigned
011

Reserved for Geographic Unicast Addresses
100

Unassigned
101

Unassigned
110

Unassigned
1110

Unassigned
1111 0

Unassigned
1111 10

Unassigned
1111 110

Unassigned
1111 1110 0

Link Local Use Addresses
1111 1110 10

Site Local Use Addresses
1111 1110 11

Multicast Addresses
1111 1111




Provider-Based Unicast Addresses
Provider-based unicast addresses are similar to the IPv4 global addresses. The format of these addresses is illustrated in figure 3-22. Descriptions of the address fields are as follows:


•  Format Prefix—First three bits are 010, indicating a provider-based unicast address.
•  REGISTRY ID—Identifies the Internet address registry that assigns the PROVIDER ID.
•  PROVIDER ID—Identifies the service provider responsible for this address.
•  SUBSCRIBER ID—Identifies which subscriber is connected to the service provider.
•  SUBNET ID—Identifies the physical link to which the address belongs.
•  INTERFACE ID—Identifies a single interface among interfaces that belong to the SUBNET ID. For example, this could be the traditional 48-bit IEEE-802 Media Access Control (MAC) address.


Figure 3-22  IPv6 address assignment hierarchy.
The IPv6 global address incorporates the CIDR functions of the IPv4 scheme. Addresses are defined in such a way as to allow hierarchy, where each entity takes its portion of the address from an entity above it, as illustrated in figure 3-23.


Figure 3-23  IPv6 address assignment hierarchy.
Local-Use Addresses
Local-use addresses are similar to the IPv4 private addresses defined in RFC 1918. Local-use addresses are divided into two types: Link-Local Use (prefix 1111111010), which are private to a particular physical segment, and Site-Local Use (prefix 1111111011), which are private to a particular site. Figure 3-24 illustrates the format of these local use addresses.


Figure 3-24  Local-use address formats.
The local-use addresses have local meaning. The link addresses have local meaning to a particular segment, and the site addresses have local meaning to a particular site.

Companies that are not connected to the Internet can easily assign their own addresses without a need for requesting prefixes from the global address space. If the company later decides to interconnect globally over the Internet, a REGISTRY ID, PROVIDER ID, and SUBSCRIBER ID will be assigned to be used with the already assigned local addresses. This is a major improvement over having to replace all private addresses with global addresses or using Network Address Translation tables to get things working in the IPv4 addressing scheme.



Previous
Table of Contents
Next