Cisco Nexus 7000 Series Configuration Manual page 68

Information About IPv6
S e n d d o c u m e n t c o m m e n t s t o n e x u s 7 k - d o c f e e d b a c k @ c i s c o . c o m .
Figure 3-1
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 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 called 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 use networks that are on the older architecture.
A subnet ID, which is a 16-bit subnet field, can be used by individual organizations to create a 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 identifies interfaces on a link. The interface ID is unique to the link. In many cases, an
interface ID is the same as or based on the link-layer address of an interface. Interface IDs used in
aggregatable global unicast and other IPv6 address types are 64 bits long and are in the modified EUI-64
format.
Interface IDs are in the modified EUI-64 format in one of the following ways:
• For all IEEE 802 interface types (for example, Ethernet, and Fiber Distributed Data interfaces), the
first three octets (24 bits) are the Organizationally Unique Identifier (OUI) of the 48-bit link-layer
address (MAC address) of the interface, the fourth and fifth octets (16 bits) are a fixed hexadecimal
value of FFFE, and the last three octets (24 bits) are the last three octets of the MAC address. The
Universal/Local (U/L) bit, which is the seventh bit of the first octet, has a value of 0 or 1. Zero
indicates a locally administered identifier; 1 indicates a globally unique IPv6 interface identifier.
For all other interface types (for example, serial, loopback, ATM, Frame Relay, and tunnel interface
•
types—except tunnel interfaces used with IPv6 overlay tunnels), the interface ID is similar to the
interface ID for IEEE 802 interface types; however, the first MAC address from the pool of MAC
addresses in the router is used as the identifier (because the interface does not have a MAC address).
For tunnel interface types that are used with IPv6 overlay tunnels, the interface ID is the IPv4
•
address assigned to the tunnel interface with all zeros in the high-order 32 bits of the identifier.
Note
Cisco Nexus 7000 Series NX-OS Unicast Routing Configuration Guide, Release 4.x
3-4
Aggregatable Global Address Format
Provider
45 bits
Global Routing Prefix
For interfaces that use the Point-to-Point Protocol (PPP), where the interfaces at both ends of the
connection might have the same MAC address, the interface identifiers at both ends of the
connection are negotiated (picked randomly and, if necessary, reconstructed) until both
identifiers are unique. The first MAC address in the router is used as the identifier for interfaces
using PPP.
Site Host
16 bits 64 bits
SLA Interface ID
Chapter 3 Configuring IPv6
OL-20002-02