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Chapter 2 IPv6 Address Configuration
There are no two network interface cards with an identical MAC address. Such addresses
can be used to uniquely identify the interfaces at the network link-layer.
The interface identifier of an IPv6 host address is based on the Institute of Electrical and
Electronics Engineers ( IEEE ) EUI-64 format, which creates a locally and globally unique
64-bit interface identifier based on the existing MAC addresses.
These 64-bit interface identifiers can address one by one globally and can uniquely identify
the interface of each network. This means that, in theory, there are up to 264 different
physical interfaces and about 1.8 x 1019 different addresses, which, however, only occupy
half of the IPv6 address space. It is enough in the foreseeable future at least.
The IPv6 unicast address can be classified into the following categories:
l
Aggregatable Global Unicast Address
This is another kind of aggregation, which is independent of an Internet Service
Provider ( ISP ). The provider-based aggregatetive addresses must be changed as
a provider changes, while the exchange-based addresses are directly located by
an IPv6 switching entity. The exchange provides address blocks, and users and
providers conclude contracts for the network access.
Such network access is either directly provided by a provider, or indirectly provided
by an exchange. However, the routing is through the exchange. In this way, a user
needs not to address again when it changes a provider. At the same time, users are
allowed to use multiple ISPs to process single-block network address.
Aggregatable global unicast addresses include all the addresses whose three starting
bits are 001, which can be used as prefixes for other unallocated unicast. Table 2-2
lists the aggregatable global unicast address fields.
Table 2-2 Aggregatable Global Unicast Address Fields
3 13 8 24 16 64
FP TLA ID RES NLA ID SLA ID Interface identifier
Table 2-2 includes the following fields.
à
FP field
This is the 3-bit format prefix in an IPv6 address, indicating to which address
category in the IPv6 address space this address belongs. Currently, the field is
001, indicating this is an aggregatable global unicast address.
à
TLA ID field
This is the top-level aggregation identifier, including the routing information about
the addresses at the highest level. Here, it refers to the routing information with
the most hosts in network interconnection. Currently, this field is 13 bits and can
obtain at most 8,192 different top level routes.
à
RES field
2-5
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