ACI DHCP Relay with Infoblox Option 82 Multiple-VRFs (Inter-VRF) - HowTo

Erich Schommarz · ‎03-26-2021

Dear Community

We are trying to implement DHCP in ACI with DHCP Relay with Multiple-VRFs (Inter-VRF). As DHCP Server customer is using Infoblox and first tests where not successfull. For info, dhcp in same VRF where DHCP Server is also located works with no special configuration on Infoblox side. Seems that Option 82 is supported out of the box.

Does anybody have experience or any tips what has to be configured on Infoblox? Enclosed some information from my side. Enclosed the DHCP Request which is forwarded from the Leaf Switch (DCHP Relay). We would like to now assign a IP Address from the Option 82 Suboption: (5) Link selection (10.200.0.0):

Internet Protocol Version 4, Src: 10.180.14.1, Dst: 10.180.14.20
User Datagram Protocol, Src Port: 67, Dst Port: 67
Dynamic Host Configuration Protocol (Discover)
    Message type: Boot Request (1)
    Hardware type: Ethernet (0x01)
    Hardware address length: 6
    Hops: 1
    Transaction ID: 0xa3f765b9
    Seconds elapsed: 0
    Bootp flags: 0x0000 (Unicast)
    Client IP address: 0.0.0.0
    Your (client) IP address: 0.0.0.0
    Next server IP address: 0.0.0.0
    Relay agent IP address: 10.180.14.1
    Client MAC address: VMware_aa:5c:9f (00:50:56:aa:5c:9f)
    Client hardware address padding: 00000000000000000000
    Server host name not given
    Boot file name not given
    Magic cookie: DHCP
    Option: (53) DHCP Message Type (Discover)
    Option: (61) Client identifier
    Option: (12) Host Name
    Option: (60) Vendor class identifier
    Option: (55) Parameter Request List
    Option: (82) Agent Information Option
        Length: 48
        Option 82 Suboption: (1) Agent Circuit ID
        Option 82 Suboption: (2) Agent Remote ID
        Option 82 Suboption: (154) Unknown
        Option 82 Suboption: (151) VRF name/VPN ID
        Option 82 Suboption: (11) Server ID Override (10.200.0.1)
        Option 82 Suboption: (5) Link selection (10.200.0.0)
    Option: (255) End
        Option End: 255
    Padding: 040ac80000ff00000000

Additional information which I have found and could help others in similar situation

If somebody has DHCP MS Server 2019, the following link gives advice what to do:
https://community.cisco.com/t5/application-centric/aci-dhcp-relay-for-ms-server-2019/m-p/3991146#M7462
- No special configuration for Option 82 required except a local Network pool where the DHCP Server is located. Otherwise DHCP Server doesn't accept the DHCP Request (Maybe for Infoblox the same is required?)
Technote Cisco, a little outdated but a lot of good information
https://community.cisco.com/t5/data-center-documents/technote-on-dhcp-relay-in-aci/ta-p/3161830
- According to that article no configuration necessary under the DHCP Pool. It just works. If something is configured under OPT 82 it will fail. But we can't have the Custom DHCP Option with relay-agent-information empty!
Infos from Infoblox about Option 82
https://docs.infoblox.com/display/nios84/About+IPv4+DHCP+Options
- It says that link selection sub-options are supported and that they must be added / configured on the DHCP relay agent. But nothing about how to assign a IP based on link selection.

If anybody has some tips would appreciate much and would be glad to test out and update this blog with according experience. It seems that a lot of people have issues with DHCP and ACI and there are not a lot of good discussions about it and hope that with this Question / Discussion I can improve this situation a little bit.

Thanks Erich