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IPv6 Addressing
Unique Local Unicast IPv6 Address
Unique Local Unicast IPv6 Address
A unique local unicast address is an address that falls within a specific range,
but is used only as a global unicast address within an organization. Traffic
having a source address within the defined range should not be allowed
beyond the borders of the intended domain or onto the public internet.
The current prefix for specifically identifying unique local unicast addresses
is fd00/8. The leftmost 64 bits of a unique local unicast address include:
■ the well-known prefix “fd”
■ a 40-bit global identifier
■ a 16-bit subnet identifier
For example:
fd73:110:255:23:215:60ff:fe7a:adc0/64
In the above case, the following values are used with the well-known prefix
and L-bit setting:
■ global identifier: 0073:110:255
■ subnet identifier: 23
■ interface identifier: 215:60ff:fe7a:adc0
Unique local unicast addresses can be assigned by router advertisements,
DHCPv6 servers, or static configuration. The boundaries for unique local
unicast address are set by border routers. Unique local unicast addresses can
be assigned in DNS servers supporting an internal network, but should not be
included in global DNS assignments.
For related information, refer to:
■ RFC 4193: “Unique Local IPv6 Unicast Addresses”