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IPv6 Network Administration by David Malone, Niall Richard Murphy

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Address Architecture

Those of you who are familiar with IPv4 networks may have encountered the notion of private versus public address space. Private address space is address space used within an organization's network, and in theory it cannot be reached from the outside world (often people like to pretend that this gives them additional security, see "NAT" in Chapter 1). These addresses are an example of address spaces with special properties—and often (but not always) these types of address space can be inferred by glancing at the address.

Examples of special addresses from the IPv4 world include the private class A space 10.0.0.0/8, which is discussed in the "Addressing Model" section in Chapter 1, and would be familiar to those building enterprise networks. Similarly 127.0.0.0/8 is the "localhost" space, which hosts use to contact themselves.

Warning

One interesting IPv4 special address is the "broadcast" address in IPv4, 255.255.255.255, because it has no direct equivalent in IPv6. Broadcasts no longer exist in IPv6, and multicast is used as the transport for contacting multiple hosts simultaneously.

Similarly in IPv6 there are a number of address spaces, usually expressed as a prefix with CIDR network length. The official breakup of this space is documented on the IANA web site http://www.iana.org/, but we summarize the allocations in Table 3-1.

Table 3-1. The breakup of the IPv6 address space

Prefix

Intended use

::0/96

Unspecified/loopback/compatible-IPv4 address

::ffff:0.0.0.0/96 ...

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