D-Link DSL-2900AL VIPER User Manual page 90

Section 4 - Configuration
Enable Automatic
Check to enable the Automatic IPv6 Address Assignment feature.
IPv6 Address
Assignment:
Autoconfiguration Select Stateful (DHCPv6), SLAAC + RDNSS or SLAAC + Stateless
Type: DHCPv6.
Router Enter the IPv6 address lifetime (in minutes).
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Lifetime:
Click Save when you are done.
D-Link DSL-2900AL User Manual 86