Autoconfiguration Of Ipv6 Addresses - Alcatel-Lucent OmniSwitch 6850-48 Network Configuration Manual

IPv6 Overview

Autoconfiguration of IPv6 Addresses

This implementation of IPv6 supports the stateless autoconfiguration of link-local addresses for IPv6
VLAN and tunnel interfaces and for devices when they are connected to the switch. Stateless refers to the
fact that little or no configuration is required to generate such addresses and there is no dependency on an
address configuration server, such as a DHCP server, to provide the addresses.
A link-local address is a private unicast address that identifies an interface or device on the local network.
This type of address allows communication with devices and/or neighboring nodes that are attached to the
same physical link. Note that when the communication is between two nodes that are not attached to the
same link, both nodes must have a configured global unicast address. Routing between link-local
addresses is not available because link-local addresses are not known or advertised to the general network.
When an IPv6 VLAN or a tunnel interface is created or a device is connected to the switch, a link-local
address is automatically generated for the interface or device. This type of address consists of the well-
known IPv6 prefix FE80::/64 combined with an interface ID. The interface ID is derived from the router
MAC address associated with the IPv6 interface or the source MAC address if the address is for a device.
The resulting link-local address resembles the following example:
FE80::2d0:95ff:fe6b:5ccd/64
Note that when this example address was created, the MAC address was modified by complementing the
second bit of the leftmost byte and by inserting the hex values 0xFF and 0xFE between the third and fourth
octets of the address. These modifications were made because IPv6 requires an interface ID that is derived
using Modified EUI-64 format.
Stateless autoconfiguration is not available for assigning a global unicast or anycast address to an IPv6
interface. In other words, manual configuration is required to assign a non-link-local address to an inter-
face. See "Assigning IPv6 Addresses" on page 26-15
Both stateless and stateful autoconfiguration is supported for devices, such as a workstation, when they are
connected to the switch. When the stateless method is used in this instance, the device listens for router
advertisements in order to obtain a subnet prefix. The unicast address for the device is then formed by
combining the subnet prefix with the interface ID for that device.
Stateful autoconfiguration refers to the use of an independent server, such as a DHCP server, to obtain an
IPv6 unicast address and other related information. Of course, manual configuration of an IPv6 address is
always available for devices as well.
Regardless of how an IPv6 address is obtained, duplicate address detection (DAD) is performed before the
address is assigned to an interface or device. If a duplicate is found, the address is not assigned. Note that
DAD is not performed for anycast addresses.
Please refer to RFCs 2462, 2464, and 3513 for more technical information about autoconfiguration and
IPv6 address notation.
page 26-8
for more information.
OmniSwitch AOS Release 6 Network Configuration Guide
Configuring IPv6
September 2009