Need global command for helper address on edge switches?

[JustTakeTheFirstStep]

interface Vlan1400
 description Configured from Catalyst Center
 mac-address 0000.0c9f.f253
 vrf forwarding VN1
 ip address 192.168.0.1 255.255.252.0
 ip helper-address 172.16.100.101
 ip helper-address 172.16.100.102
 no ip redirects
 ip route-cache same-interface
 no lisp mobility liveness test
 lisp mobility 192_168_0_0-VN1

DNAC version 2.3.7.7-70047

I used Lan-automation on the EDGE switch.
The EDGE switch interface is missing the global option for helper-address.
The PC does not get an IP assignment.

IP binding fails when helper-address is 172.16.100.1
IP binding succeeded with helper-address global 172.16.100.1

[Andrii Oliinyk]

it's bc 172.16.100.1 is in different VRF. CatC Design/NetworkSettings for DHCP servers per IP-pool doesnt support manipulation with this flag. 

[JustTakeTheFirstStep · Accepted solution]

https://www.cisco.com/c/en/us/td/docs/cloud-systems-management/network-automation-and-management/dna-center/tech_notes/sda_dhcp/b_cisco_sda_dhcp.html

interface Vlan3000
 description Configured from apic-em
 mac-address 0000.0c9f.fc17
 vrf forwarding VRF1
 ip address 192.168.101.1 255.255.255.0
 ip helper-address 192.168.103.2 --> Note that the "global" keyword has been removed. DHCP discovery goes through the overlay.

The DHCP server is not on the same subnet.
According to the guide, DNAC no longer uses the global option for helper-address.
We allowed ports 67,68 on the firewall and everything was solved.

[Andrii Oliinyk]

it's not about subnet but about VRF space. CatC configures helpers under IP-pool w/o any extra stuff like using GRT(INFRA_VN) for DHCP-exchange. Thus to have your DHCP-servers in different VRF & still use it for overlay IP-pools u have enable communications between that VRFs somewhere. Implementing it with FWs in some "central" locations is one of the approaches.