Enabling DHCPv6

Enabling the DHCPv6 option on a VLAN allows the switch to obtain a global unicast address and an NTP (network time protocol) server assignment for a Timep server. (If a DHCPv6 server is not necessary to provide a global unicast address to a switch interface, the server can still be configured to provide the NTP server assignment. It is sometimes referred to as “stateless DHCPv6”.)

Syntax:

ipv6 address dhcp full [rapid-commit]

no ipv6 address dhcp full [rapid-commit]

Configures DHCPv6 on a VLAN, which initiates transmission of DHCPv6 requests for service. If IPv6 is not already enabled on the VLAN by the ipv6 enable command, this option enables IPv6 and causes the switch to autoconfigure a link-local unicast address with an EUI-64 interface identifier.

[rapid-commit]

Expedites DHCP configuration by using a two-message exchange with the server (solicit-reply) instead of the default four-message exchange (solicit-advertise-request-reply).

NOTE:

A DHCPv6 server does not assign link-local addresses, and enabling DHCPv6 on a VLAN does not affect a pre-existing link-local address.

A DHCPv6-assigned address can be configured on a VLAN when the following is true:

  • The assigned address is not on the same subnet as a previously configured autoconfig address.

  • The maximum IPv6 address limit on the VLAN or the switch has not been reached.

If the switch is an IPv6 host, ipv6 address dhcp full must be configured on the DHCPv6 client to obtain relevant information from the DHCPv6 server. M-bit and O-bit settings in RAs from a router are not used by the switch in host mode. If the switch is operating as an IPv6 router, it includes M-bit and O-bit values in the RAs it transmits. See IPv6 Router Advertisements (RAs) for routing switch operation.

If a DHCPv6 server responds with an IPv6 address assignment, this address is assigned to the VLAN. (The DHCPv6- assigned address will be dropped if it has the same subnet as another address already assigned to the VLAN by an earlier autoconfig command.)

An IPv6 address assigned to the VLAN by a DHCPv6 server is set to the preferred and valid lifetimes specified in an RA received on the VLAN for the prefix used in the assigned address. It is configured as a preferred address after verification of uniqueness by DAD.

Default: Disabled

If no other IPv6-enabling command is configured on the VLAN, the no form of the command removes the DHCPv6 option from the configuration and disables IPv6 on the VLAN See Disabling IPv6 on a VLAN.