KB.15.15

before the address became deprecated. However, in this time frame, the address should no longer

be used for new communications. If this time expires without the deprecated address being refreshed,

the address becomes invalid and may be assigned to another interface.

Table 1 IPv6 unicast addresses lifetimes

Lifetime criteriaAddress source

PermanentLink-local

PermanentStatically configured unicast

Finite preferred and valid lifetimesAutoconfigured global

Finite preferred and valid lifetimesDHCPv6-configured

A new, preferred address used as a replacement for a deprecated address can be acquired from

a manual, DHCPv6, or autoconfiguration source.

DHCPv6 client

The DHCPv6 client allows a host to request global unicast IPv6 address assignments from a DHCPv6

server. If there are multiple DHCPv6 servers, the client can select a server based on the preference

value sent in DHCPv6 messages.

The DHCPv6 client can request that the server send only the configuration information. In this case,

a router on the same interface (VLAN) as the host provides the global IPv6 address to the host

through router advertisements.

NOTE: If the switch is rebooted with a default configuration, only the default DHCPv4 client is

enabled on the default VLAN. The DHCPv6 client has to be explicitly enabled on a VLAN using

the command ipv6 address dhcp or ipv6 address autoconfig.

Duplicate address detection (DAD) for statically configured addresses

Statically configured IPv6 addresses are designated as permanent. If DAD determines that a

statically configured address duplicates a previously configured and reachable address on another

device belonging to the VLAN, the more recent, duplicate address is designated as duplicate.

IPv6 loopback interfaces

By default, each switch has eight internal IPv6 loopback interfaces (lo-0 as through lo-7) with

IPv6 address ::1/128 configured by default on lo-0. This address (::1/128) is used only for

internal traffic transmitted within the switch and is not used in packet headers in egress traffic sent

to network devices.

Each loopback interface can have multiple IPv6 addresses, all of which must be unique. Routing

protocols such as OSPFv3, advertise the configured loopback addresses throughout a network or

autonomous system.

User-defined IPv6 loopback addresses provide these benefits when a routing protocol is enabled:

• A loopback interface is a virtual interface that is always up and reachable as long as at least

one of the IPv6 interfaces on the switch is operational. As a result, a loopback interface is

useful for debugging tasks because its address can always be pinged if any other switch

interface is up.

• You can use a loopback interface to establish a Telnet session, ping the switch, and access

the switch through SNMP.

For information about how to configure an IPv6 loopback address to participate in an OSPF

broadcast area, see “Assigning IPv6 loopback addresses to an area (optional)” (page 214).

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