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TECHNOTE on DHCP Relay in ACI

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DHCP Relay in ACI

Overview, Configuration, Troubleshooting, and Caveats\Issues

 

DHCP Relay Overview

While ACI fabric-wide flooding is disabled by default, flooding within a bridge domain is enabled by default. Because flooding within a bridge domain is enabled by default, clients can connect to DHCP servers within the same EPG. However, when the DHCP server is in a different EPG, BD, or context (VRF) than the clients, DHCP Relay is required. Also, when Layer 2 flooding is disabled, DHCP Relay is required.

 

This attached document has all of the details related to "DHCP Relay in ACI"

Version 10, updated August 21, 2017

 

The latest technote revision contains updates in regards to "Option 82 Suboption: Link selection” support in Windows 2016 Server.  And I have added some notes on Infoblox DHCP Services in an ACI Deployment.

 

Note: If you use Windows 2016 Server in an "INTER-VRF" setup, Microsoft requires you to setup a "dhcp scope" for the "Server's" local subnet before it will server DHCP addresses. If you do NOT setup a local DHCP scope, your DHCP requests can get a NACK DHCP Response.

 

 

Comments
Beginner

Hi Tomas,

Would like to add one more important point here regarding interoperability of Cisco ACI with the DHCP server built on MS Windows 2016:

 

An IP scope needs to be defined on the server for either the scope of the DHCP Server's subnet or the subnet in ACI which is the exit point of the VRF otherwise you may see a NACK.

 

One of the issue that we came across recently.

 

ACI version: 2.3(1f)

 

Thanks,

Jayesh

Cisco Employee

Hi Jayesh,

We have updated the main post which links the PDF to include a note of this requirement.

-Ray

Beginner

Appreciate your quick response Ray, Tomas!

 

Thanks,

Jayesh

Beginner

Dear Tomas,

 

Thanks for the most helpful document. I found one more addition for you to confirm and add in your document:

 

When DHCP Server and Client are in different Tenants:

we need a Contract (Inter-Tenant, Export, Provided, Consumed Contract Interface etc.)

 

Post the above additions my DHCP client was able to get dynamic IP from DHCP server. 

Could you please let me know if this (Contract) is a correct way or we have a better way.

 

PS: I used 'default/common" filter. I think we can also use UDP-67 & 68 (bi-directional)

 

Merci beacoup

Ash

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