source ip is 0

[petercinvest]

we use sw1-sw2-R1, r1 is dhcp server, Sw1 is doing dhcp snooping, and enable inform option.  

sw2 specify the ip helper address R1,  but it didn't use ip dhcp relay info trust.

so in this case, does souce ip address is 0.0.0.0 and giaddr=0 when i capture packet between sw1 and sw2? thanks

[devils_advocate]

When a host does a DHCPDISCOVER, the Source IP is going to be 0.0.0.0.

From your setup, it sounds like a L2 connection between Sw1 and Sw2 meaning the source ip address will stay as all zeros.

Once it hits Switch 2, and the IP Helper gets invoked, the Source IP will change to the interface IP address before the frame is forwarded to the DHCP Server. 

According to this guide, the GI Address also changes to be Switch 2's interface IP once the IP Helper is invoked:

http://www.cisco.com/c/en/us/support/docs/ip/dynamic-address-allocation-resolution/27470-100.html