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IPv6 Addressing Configuration
Address Lifetimes
Address Lifetimes
Every configured IPv6 unicast and anycast 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 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 will both appear in the show ipv6 vlan < vid > output
as long as the deprecated address is within its valid lifetime.
Valid Lifetime
This is the total time the address is available, and 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 timeframe, the address should no longer be used for new communica-
tions. If this time expires without the deprecated address being refreshed, the
address becomes invalid and may be assigned to another interface.
Sources of IPv6 Address Lifetimes
Manually configured addresses have permanent lifetimes. The prefixes
received from router advertisements for global unicast addresses include
finite valid and preferred lifetime assignments. Refer to “Unicast Address
Prefixes” on page 3-11.