DHCP server or DHCP relay may not work properly on all interfaces if DHCP discovers are seen on more than one interface unit belonging to different security zones.
J-Series or SRX acting as DHCP relay agent or DHCP server may not be able to respond to DHCP requests if there are more than one interfaces which receive DHCP discover messages and the interface units belong to different security zones. The reason why this happens is that DHCP discovers are broadcast packets for which a session is created. When another DHCP broadcast message is received on different interface unit belonging to a different security zone, another broadcast session would need to be created which would overlap the existing broadcast session on the reverse wing. Therefore the second session would not be allowed to be created until the first session has aged out.
In later releases, JUNOS will no longer create a flow session for DHCP broadcasts. Therefore this would avoid conflicting sessions. The following releases have this resolution.