When local DHCP server redundancy or synchronization is used, using address-range failover local | remote, in conjunction with PPPoE in multi-chassis environment, both DHCP servers must be referenced under the corresponding group interface on each node. For address-range failover access-driven configurations only one DHCP server must be referenced.
subscriber-interface <ip-int-name>
group-interface <ip-int-name>
dhcp
server <local-dhcp-ip-address> <remote-dhcp-ip-address>
Otherwise, the PPPoE clients are not synchronized by MCS.
This is not the requirement in the IPoE environment. In the IPoE environment, it is enough that the DHCP server points to the IP address of the local DHCP server. If the IP lease is originally assigned by the peer DHCP server, the request for renewal is automatically forwarded to the remote DHCP server by the virtue of the IP address of the original DHCP server that is included in the renewal request.
It is necessary for the successful renewal of the IP address on the remote DHCP server, that the remote DHCP server has a valid return path back to the gi-address of the forwarder of the renewal request.