02-26-2011 11:13 AM
There is no similar to ip dhcp smart-relay command in JUNOSe, and uRPF check is done by ip sa-validate.
The description of ip dhcp smart-relay command from cisco.com:
Allows the DHCP relay agent to switch the gateway address (giaddr field of a DHCP packet) to secondary addresses when there is no DHCPOFFER message from a DHCP Server.
It should be possible to configure your DHCP Server to send DHCP Offer when packet is received with giaddr field set to primary address of the interface.