IPv6 Configuration Guide K/KA/KB.15.15

In Figure 20 (page 208) , router "X" is a relay agent configured to forward DHCPv6 service requests
received from VLAN 10 to the "all-DHCPv6-servers" multicast helper address (FF05::1:3) through
VLAN 14. Router "Z" receives the request from router "X" on VLAN 14. Because router "Z" is
configured with unicast helper address 2001:db8:0:15::33 on VLAN 14, the service request is
relayed to the DHCPv6 server at 2001:db8:0:15::33 on VLAN 15. (In this example, both router
"X" and router "Z" act as DHCPv6 relay agents.)
Figure 20 Routing a multicast DHCPv6 request across a multiple-hop topology
Router "X": Relay Agent
VLAN-10:
2001:db8:0:10::1
Multicast helper address =
all-dhcp-servers
egress vlan 14
VLAN-14:2001:db8:0:14::1
Router "Y"
VLAN-B:
2001:db8:0:12::10
VLAN-A:
2001:db8:0:10::2
DHCPv6 Server
2001:db8:0:2::11
Client
DHCPv6 Server
2001:db8:0:15::33
VLAN-14
Router "Z"
VLAN-E:
2001:db8:0:15::1
VLAN-D:
2001:db8:0:14::2
VLAN-15
VLAN-10
VLAN-12
A multi-hop relay scenario such as is shown in Figure 20 (page 208) requires the following:
• All relays in the path except the relay closest to the server have a multicast helper address.
• The last relay in the path to the server has a unicast helper address.
Thus, if router "Z" was not configured with a helper address as shown above, the relayed service
request would be restricted to VLAN 14 and would not reach the server at 2001:db8:0:15::33
on VLAN 15.
208 DHCPv6-Relay