22.1.3 Relay operation

(1) Granting ID of Interfaces

The IPv6 DHCP relay attaches an interface ID to the IPv6 DHCP packets to be forwarded to the IPv6 DHCP server. The interface ID is used to identify the destination when the IPv6 DHCP server sends a reply packet to IPv6 DHCP clients.

The following figure describes the format of an interface ID that is set to the Interface-ID Option.

Figure 22-2: Format of Interface-id informations

(2) Operation when the device address (loopback 0 interfaces) is set

When the IPv6 DHCP relay forwards an IPv6 DHCP packet to the IPv6 DHCP server and the device address has been configured by using the interface loopback 0 or ipv6 address configuration command on the Switch, the IPv6 DHCP relay sets the device address as the source address.

When the device address is not configured, the IPv6 DHCP relay uses the address of the output interface on the IPv6 DHCP server side as the source address. If a failure occurs on an interface on the priority route between the IPv6 DHCP server and the IPv6 DHCP relay, even when redundant routes exist between them, the IPv6 DHCP clients cannot receive the IPv6 DHCP relay packet that was forwarded by the IPv6 DHCP relay before the failure.

When the device address is configured, the IPv6 DHCP server sends IPv6 DHCP packets to the address that is unique to the Switch, and not to specific interfaces. Therefore, if an error occurs on an interface on the priority route, the interface on a redundant route can receive the IPv6 DHCP packets.