IPv6 Configuration Guide K/KA/KB.15.15

1. Ensure that there is a route configured between a DHCPv6 server and the routing switch and
that the server is configured to support host requests forwarded from the routing switch.
2. For each VLAN on which you want the routing switch to provide DHCPv6-relay services,
determine the helper addresses the relay agent should have for forwarding client DHCPv6
requests to reachable DHCPv6 servers. You can configure one or more helper addresses and
can use either or both of the following types:
Unicast
Specifies the global unicast address of a specific DHCPv6 server.
Multicast
Specifies a group of DHCPv6 servers (well-known or user-defined) in a defined network
scope and group identification. (For more information on this topic, see section 2.7,
"Multicast Addresses" in RFC 4291.) This option includes specifying the VLAN interface
on which requests to a given multicast address will exit from the routing switch.
3. In each VLAN context where DHCPv6-relay service is needed, use the ipv6 helper-address
unicast / multicast command to configure one or more DHCPv6 helper addresses.
4. In the global config context, use the dhcpv6-relay command to globally enable DHCPv6
relay on the routing switch.
5. If IPv6 routing is not already enabled on the routing switch, use the ipv6 unicast-routing
command in the global config context to enable IPv6 routing.
6. On each VLAN where you have configured a helper address, ensure that the target DHCPv6
server is reachable.
Multiple-hop forwarding of DHCPv6 service requests
If a routing switch receives a unicast DHCPv6 service request forwarded by a relay agent, the
request is routed to the specified server. For example, in Figure 19 (page 207), router "X" is a relay
agent configured to forward DHCPv6 requests received from VLAN 10 to unicast helper address
2001:db8:0:12::11. Router "Y" receives the request from router "X" on VLAN 10 and routes it to
the DHCPv6 server at 2001:db8:0:12::11 on VLAN 12. In this case, router "Y" acts as an IPv6
router and not as a DHCPv6 relay.
Figure 19 Routing a unicast DHCPv6 request across a multiple-hop topology
Router "X": Relay Agent
VLAN-10:
2001:db8:0:10::1
Unicast helper address =
2001:db8:0:12::11
VLAN-14:2001:db8:0:14::1
Router "Y"
VLAN-12:
2001:db8:0:12::10
VLAN-10:
2001:db8:0:10::2
DHCPv6 Server
2001:db8:0:12::11
Client
DHCPv6 Server
2001:db8:0:15::33
VLAN-12
Router "Z"
VLAN-15:
2001:db8:0:15::1
VLAN-14:2001:db8:0:14::2
VLAN-14
VLAN-10
VLAN-15
Multiple-hop forwarding of DHCPv6 service requests 207