IOS-XR ASR 9k dhcp relay

When trying to configure dhcp in ASR 9k, got into some problems.
First, ASR 9k does not have dhcp server, at least till version 4.3.2. You will always need a external dhcp server. 
So, when configuring dhcp relay to my corporate dhcp, here's what I found:

Does not work:
interface  bvi2
   ipv4 helper-address vrf CORP 10.1.100.10
   ipv4 helper-address vrf CORP 10.2.100.10

Works:
dhcp ipv4
 profile CORP_DHCP relay
  helper-address vrf CORP 10.1.100.10
  helper-address vrf CORP 10.2.100.10
!
dhcp ipv4 interface bvi2 relay profile CORP_DHCP


Hope it helps! Regards