command specifies a destination address to which client messages are forwarded
and enables DHCP for IPv6 relay service on the interface. When relay service is
enabled on an interface, a DHCP for IPv6 message received on that interface is
forwarded to all configured relay destinations. The incoming DHCP for IPv6
message may have come from a client on that interface, or it may have been
relayed by another relay agent.
destination can be a unicast address of a server or another relay agent, or it
may be a multicast address. There are the following two types of relay
- A link-scoped unicast or
multicast IPv6 address, for which a user must specify an output interface
- A global unicast IPv6
address, for which a user can specify an output interface for this kind of
- A global or site-scope
multicast IPv6 address, for which a user can specify an output interface for
this kind of address if 'mhost ipv6 default-interface' is specified.
If no output
interface is configured for a destination, the output interface is determined
by routing tables. In this case, it is recommended that a unicast or multicast
routing protocol be running on the router.
destinations can be configured on one interface, and multiple output interfaces
can be configured for one destination. When the relay agent relays messages to
a multicast address, it sets the hop limit field in the IPv6 packet header to
loopback, and node-local multicast addresses are not acceptable as the relay
destination. If any one of them is configured, the message "Invalid destination
address" is displayed.
Note that it is not
necessary to enable the relay function on an interface for it to accept and
forward an incoming relay reply message from servers. By default, the relay
function is disabled, and there is no relay destination on an interface. The
no form of the
command removes a relay destination on an interface or deletes an output
interface for a destination. If all relay destinations are removed, the relay
service is disabled on the interface.
The DHCP for IPv6
client, server, and relay functions is mutually exclusive on an interface. When
one of these functions is already enabled and a user tries to configure a
different function on the same interface, one of the following messages is
displayed: “Interface is in DHCP client mode,” “Interface is in DHCP server
mode,” or “Interface is in DHCP relay mode.”