Reports the valid lifetime, in seconds, that the client requests for its IPv6 address -- the duration after which the address becomes fully unusable if not renewed. Alongside the preferred lifetime request, this defines the outer bound the client is asking the server to honor, so an address that expires sooner than expected on this interface is a sign the DHCPv6 server granted a shorter valid lifetime than what's shown here. A typical request might be 2592000 seconds (30 days), giving the client a full month before the address would need to be renewed or it drops off the interface.