As specified in RFC 3046, DHCP Relay Agent Information Option, an SR OS Relay Agent discards a DHCP packet where the gi address is set to 0.0.0.0 but with a Relay Agent Information Option 82 present, unless it arrives on a ‟trusted” circuit.
The dhcp trusted command enables the Relay Agent to forward such DHCP requests. The gi address is updated according the gi-address configuration on the interface.