topic Re: Need global command for helper address on edge switches? in Software-Defined Access (SD-Access)

Need global command for helper address on edge switches?

JustTakeTheFirstStep — Mon, 10 Mar 2025 02:38:43 GMT

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

Re: Need global command for helper address on edge switches?

Andrii Oliinyk — Mon, 10 Mar 2025 06:42:44 GMT

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.

Re: Need global command for helper address on edge switches?

JustTakeTheFirstStep — Mon, 10 Mar 2025 10:07:56 GMT

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.

Re: Need global command for helper address on edge switches?

Andrii Oliinyk — Mon, 10 Mar 2025 10:21:30 GMT

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.