Ipv6 Address Prefix Format; Ipv6 Address Type: Unicast; Global Addresses - Cisco AP775A - Nexus Converged Network Switch 5010 Configuration Manual

Chapter 54 Configuring IPv6 for Gigabit Ethernet Interfaces
S e n d d o c u m e n t a t i o n c o m m e n t s t o m d s f e e d b a c k - d o c @ c i s c o . c o m

IPv6 Address Prefix Format

An IPv6 address prefix, in the format ipv6-prefix/prefix-length, can be used to represent bit-wise
contiguous blocks of the entire address space. The ipv6-prefix is specified in hexadecimal using 16-bit
values between the colons. The prefix-length is a decimal value that indicates how many of the
high-order contiguous bits of the address comprise the prefix (the network portion of the address). For
example, 2001:0DB8:8086:6502::/32 is a valid IPv6 prefix.

IPv6 Address Type: Unicast

An IPv6 unicast address is an identifier for a single interface on a single node. A packet that is sent to a
unicast address is delivered to the interface identified by that address. The Cisco MDS NX-OS supports
the following IPv6 unicast address types:
•
•

Global Addresses

Global IPv6 addresses are defined by a global routing prefix, a subnet ID, and an interface ID.
Figure 54-1
Figure 54-1
3
001
Addresses with a prefix of 2000::/3 (001) through E000::/3 (111) are required to have 64-bit interface
identifiers in the extended universal identifier (EUI)-64 format. The Internet Assigned Numbers
Authority (IANA) allocates the IPv6 address space in the range of 2000::/16 to regional registries.
The aggregatable global address typically consists of a 48-bit global routing prefix and a 16-bit subnet
ID or Site-Level Aggregator (SLA). In the IPv6 aggregatable global unicast address format document
(RFC 2374), the global routing prefix included two other hierarchically structured fields named
Top-Level Aggregator (TLA) and Next-Level Aggregator (NLA).The IETF decided to remove the TLS
and NLA fields from the RFCs because these fields are policy-based. Some existing IPv6 networks
deployed before the change might still be using networks based on the older architecture.
A 16-bit subnet field called the subnet ID could be used by individual organizations to create their own
local addressing hierarchy and to identify subnets. A subnet ID is similar to a subnet in IPv4, except that
an organization with an IPv6 subnet ID can support up to 65,535 individual subnets.
An interface ID is used to identify interfaces on a link. The interface ID must be unique to the link. They
may also be unique over a broader scope. In many cases, an interface ID will be the same as, or based
on, the link-layer address of an interface, which results in a globally unique interface ID. Interface IDs
used in aggregatable global unicast and other IPv6 address types must be 64 bits long and constructed
in the modified EUI-64 format.
OL-17256-03, Cisco MDS NX-OS Release 4.x
Global addresses
Link-local addresses
shows the structure of a global address.
Global Address Format
Provider
45 bits
Global routing prefix
Site Host
16 bits 64 bits
SLA Interface ID
Cisco MDS 9000 Family Fabric Manager Configuration Guide
About IPv6
54-3