In the DHCPv4 client, each logical interface is independent and is an administrative unit. You can configure specific logical interfaces to run DHCP by specifying a value for CLIENT_ID in the dhcpagent configuration file. For example:
DHCPv6 works differently because the zeroth logical interface (also known as the "physical" interface) on an IPv6 interface, unlike IPv4, is always a link-local. A link-local is used to automatically assign an IP address to a device in an IP network when no other assignment method is available, such as a DHCP server. Because the zeroth logical interface cannot be under DHCP control, even though DHCPv6 is run on the zeroth logical interface it assigns addresses only on non-zero logical interfaces.
In response to a DHCPv6 client request, the DHCPv6 server returns a list of addresses for the client to configure.