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3-6
Cisco Nexus 7000 Series NX-OS Unicast Routing Configuration Guide, Release 4.x
OL-20002-02
Chapter 3 Configuring IPv6
Information About IPv6
Figure 3-3 IPv4-Compatible IPv6 Address Format
Unique Local Addresses
A unique local address is an IPv6 unicast address that is globally unique and is intended for local
communications. It is not expected to be routable on the global Internet and is routable inside of a limited
area, such as a site and it may be routed between a limited set of sites. Applications may treat unique
local addresses like global scoped addresses.
A unique local address has the following characteristics:
• It has a globally unique prefix (it has a high probability of uniqueness).
• It has a well-known prefix to allow for easy filtering at site boundaries.
• It allows sites to be combined or privately interconnected without creating any address conflicts or
requiring renumbering of interfaces that use these prefixes.
• It is ISP-independent and can be used for communications inside of a site without having any
permanent or intermittent Internet connectivity.
• If it is accidentally leaked outside of a site via routing or Domain Name Server (DNS), there is no
conflict with any other addresses.
Figure 3-4 shows the structure of a unique local address.
Figure 3-4 Unique Local Address Structure
52727
::192.168.30.1
= ::C0A8:1E01
IPv4 address0
96 bits 32 bits
•
•
•
•
FC00
Global ID 41 bits
/48 /64
Local IPv6
/7
Interface ID
Prefix — FC00::/7 prefix to identify local IPv6 unicast addresses.
Global ID — 41-bit global identifier used to create a globally unique prefix.
Subnet ID — 16-bit subnet ID is an identifier of a subnet within the site.
Interface ID — 64-bit IID
Link prefix
Subnet prefix
232389
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