Information Technology Reference
In-Depth Information
addresses. As shown in Figure 9-4, the format of the unique local address is an FP of 1111
110 (FC00::/7) followed by global ID, followed by the subnet ID and then the 64-bit inter-
face identifier (ID). The bit labeled L is set to 1 if the prefix is locally assigned, and setting
it to 0 has not been defined.
7 Bits
40 Bits
16 Bits
64 Bits
FC00::/7
Global ID
Subnet ID
Interface ID
L
1111 110
Figure 9-4
IPv6 Unique Local Address
Global Aggregatable IPv6 Address
Global aggregatable unicast addresses allow the aggregation of routing prefixes. This al-
lows a reduction of the number of routes in the global routing table. These addresses are
used in links to aggregate (summarize) routes upwards to the core in large organizations or
to ISPs. Global aggregatable addresses are identified by the fixed prefix of 2000:/3. As
shown in Figure 9-5, the format of the global aggregatable IPv6 address is a global routing
prefix starting with binary 001, followed by the subnet ID and then the 64-bit interface
identifier (ID). The device MAC address is normally used as the interface ID.
48 Bits
16 Bits
64 Bits
Global Routing Prefix
Subnet ID
Interface ID
001
Figure 9-5
IPv6 Link-Local Address Format
IPv4-Compatible IPv6 Address
IPv4-compatible IPv6 addresses begin with 96 binary 0s (six 16-bit groups) followed by
the 32-bit IPv4 address, as in 0:0:0:0:0:0:130.100.50.1 or just ::130.100.50.1. IPv4-compati-
ble IPv6 addresses have been deprecated since updated transition mechanisms no longer
require this format.
IPv6 Anycast Addresses
The IPv6 anycast (one-to-nearest) address identifies a set of devices. An anycast address
Key
To p i c
mon characteristics and are explicitly configured for anycast.
 
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