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setting the universal/local (U/L) bit--the seventh bit of the first octet--to a value of 0 or 1. A
value of 0 indicates a locally administered identifier; a value of 1 indicates a globally unique
IPv6 interface identifier.
Take MAC address 0012:0B0A:2D51 as an example. Insert FFFE to the middle of the address
to get 0012:0BFF:FE0A:2D51. Then set the U/L bit to 1 to obtain an interface ID in EUI-64
format as 0212:0BFF:FE0A:2D51.
IPv6 unicast address can be classified into several types, as shown in Table 4-1. The two
most
common types are introduced below:
Global unicast address
A Global unicast address is an IPv6 unicast address that is globally unique and is routable on
the global Internet.
Global unicast addresses are defined by a global routing prefix, a subnet ID, and an interface
ID. The IPv6 global unicast address starts with binary value 001 (2000::/3). The global routing
prefix is a value assigned to a site (a cluster of subnets/links) by IANA. The subnet ID is an
identifier of a subnet within the site.
The figure below shows the structure of a global unicast address.
Figure 4-8 Global Unicast Address Format
Link-local address
A link-local address is an IPv6 unicast address that can be automatically configured on any
interface using the link-local prefix FE80::/10 (1111 1110 10) and the interface identifier in the
modified EUI-64 format. Link-local addresses are used in the neighbor discovery protocol and
the stateless autoconfiguration process. Nodes on a local link can use link-local addresses to
communicate. The figure below shows the structure of a link-local address.
Figure 4-9 Link-local Address Format
IPv6 devices must not forward packets that have link-local source or destination addresses to
other links.
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