Address lifetimes

Every configured IPv6 unicast address has a lifetime setting that determines how long the address can be used before it must be refreshed or replaced. Some addresses are set as "permanent" and do not expire. Others have both a "preferred" and a "valid" lifetime that specify the duration of their use and availability.

Preferred and valid address lifetimes

Autoconfigured IPv6 global unicast addresses acquire their valid and preferred lifetime assignments from RAs. A valid lifetime is the time period during which an address is allowed to remain available and usable on an interface. A preferred lifetime is the length of time an address is intended for full use on an interface, and must be less than or equal to the address's valid lifetime.

Valid and preferred lifetimes

Valid and preferred lifetimes

Preferred lifetime

This is the length of time during which the address can be used freely as both a source and a destination address for traffic exchanges with other devices. This time span is equal to or less than the valid lifetime also assigned to the address. If this time expires without the address being refreshed, the address becomes deprecated and should be replaced with a new, preferred address. In the deprecated state, an address can continue to be used as a destination for existing communication exchanges but is not used for new exchanges or as a source for traffic sent from the interface. A new, preferred address and its deprecated counterpart both appear in the show ipv6 vlan <vid> output as long as the deprecated address is within its valid lifetime.

Valid lifetime

The valid lifetime, which is the total time the address is available, is equal to or greater than the preferred lifetime. The valid lifetime enables communication to continue for transactions that began 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.

[NOTE: ]

NOTE: Preferred and valid lifetimes on a VLAN interface are determined by the RAs received on the interface. These values are not affected by the lease time assigned to an address by a DHCPv6 server. That is, lease expiration on a DHCPv6-assigned address terminates use of the address, regardless of the status of the RA-assigned lifetime, and router-assigned lifetime expiration of a leased address terminates the switch’s use of the address. (The router-assigned lifetime can be extended by receipt of a new RA.) Statically configured IPv6 addresses are regarded as permanent addresses, and do not expire.

IPv6 unicast addresses lifetimes

Address source Lifetime criteria
Link-local Permanent
Statically configured unicast Permanent
Autoconfigured global Finite preferred and valid lifetimes
DHCPv6-configured Finite preferred and valid lifetimes

A new, preferred address used as a replacement for a deprecated address can be acquired from a manual, DHCPv6, or autoconfiguration source.

Related Information:

  • RFC 2462: “IPv6 Stateless Address Autoconfiguration”

  • RFC 4291: “IP Version 6 Addressing Architecture”