22.1.6 Notes on using IPv6 DHCP relays

(1) Coexistence with IPv6 DHCP servers function

You cannot run both an IPv6 DHCP relay and the IPv6 DHCP server functionality simultaneously on the Switch. If you run an IPv6 DHCP relay, use the no service ipv6 dhcp configuration command to disable the IPv6 DHCP server functionality beforehand.

(2) Compatibility with IPv6 multicast functionality

When you use both IPv6 multicasting and an IPv6 DHCP relay simultaneously on the Switch, we recommend that you specify the unicast address of each IPv6 DHCP server as a relay destination of the IPv6 DHCP relay. If you want to use a multicast to all IPv6 DHCP servers, note the following:

• When you specify the all-servers multicast address as the relay destination of the IPv6 DHCP packets sent from the Switch and use IPv6 multicasting at the same time, the configuration below is required on the partner router. For details about the configuration, see the router documentation.

  • Specify the maximum value within the VLAN as the link-local address of the interface to which the Switch is connected so the Switch becomes the designated router (DR) of the IPv6 multicast routing protocol.

• Configure IPv6 multicasting on the Switch and the partner router so that the partner router becomes the rendezvous point.

(3) Notes on IPv6 DHCP Relay Packet Forwarding

• When both of the following conditions are met, IPv6 DHCP relays cannot correctly relay reply packets to IPv6 DHCP clients:

  • An IPv6 global address is not set for the interface that is specified as the packet destination by using the ipv6 dhcp relay destination configuration command.

  • The interface ID appended by the Switch when it relayed packets is not contained in the reply packets from the IPv6 DHCP server.

• The Switch can forward IP packets when the packet size is 1500 bytes or less and the packets are not fragmented.

(4) Notes on using loopback address

The configuration below is required on a router when the router is positioned between the Switch and an IPv6 DHCP server, the all-servers multicast address is specified as the destination for IPv6 DHCP packets, and an IPv6 address is set for the loopback interface. For details about the configuration, see the router documentation.

• Configure the router so that it treats the IPv6 address set for the loopback interface of the Switch as the server that is directly connected to the router and the router functions.