Overview

Since ACI release 3.1(1) it’s possible to use some Leaf Uplinks as Downlink Ports. This could help you out if there is a need for some 40/100G ports but you are currently only running 10/25G Leafs.

Currently (July 2023 update), the following Leafs support the conversion:

• N9K-C9348GC-FXP1
• N9K-C93180LC-EX
• N9K-C93180YC-EX
• N9K-C93180YC-FX
• N9K-C93180YC-FX3
• N9K-C93108TC-EX2
• N9K-C93108TC-FX2
• N9K-C93108TC-FX3
• N9K-C9336C-FX2
• N9K-93240YC-FX2
• N9K-C93216TC-FX2
• N9K-C93360YC-FX2
• N9K-C93600CD-GX
• N9K-C9364C-GX
• N9K-C9316D-GX

Limitations

There are some limitations, details can be found on the Cisco Page for ACI Version 3.2, for ACI Version 4.2 or for ACI Version 5.2

Overview of the limitations

The following table provides an overview over the Switches that support the conversion and on which ports.

Our use case

Our use case was to use some of the 40/100G Uplink Ports as Downlinks on a N9K-C93180YC-FX. The main limitation there is that the last 2 ports (53 and 54) don’t support conversion, no issue if you use them as Uplinks anyway. Otherwise you have move first your Uplinks to 53/54 and then convert the ports to Downlinks.

Conversion process

The conversion process is pretty straight forward.
Head to Fabric -> Inventory, open up the respective POD and select your Leaf.

Go to the “Interface” tab and change the mode to “Configuration”

Now select the port you want to change from uplink to downlink and then select “Downlink”.

There will be a popup with the information about the change, “Submit” it.

And that’s it, repeat for all the other interfaces you want to convert. Then reload the Leaf.

After the switch is back up, you got the 40/100G Downlink ports ready to use.

API conversion

If you want to automate the interface conversion process and use the ACI API for that, then that’s possible as well. The biggest challenge is always to find the right API calls and the needed classes.

But I can help you with that so that the interface conversion from Uplink to Downlink (or in the other direction) is easy for you.

Convert the Interface

POST to the URL https://{{ip}}/api/node/mo/uni/infra.json

Use the following Body and modify the Node and Port as requested.

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{
  "infraInfra": {
    "attributes": {},
    "children": [
      {
        "infraPortDirecPol": {
          "attributes": {
            "status": "created,modified"
          },
          "children": [
            {
              "infraRsPortDirection": {
                "attributes": {
                  "tDn": "topology/pod-1/paths-111/pathep-[eth1/49]",
                  "direc": "DownLink"
                }
              }
            }
          ]
        }
      }
    ]
  }
}

XML

Thanks to the comment from KK76, this is the way through XML

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<infrainfra>
    <infraportdirecpol>
        <infrarsportdirection tdn="topology/pod-1/paths-101/pathep-[eth1/51]" direc="DownLink"/>
    </infraportdirecpol>
</infrainfra>

Reload

As mentioned, you need to reload the leaf for the interface conversion to become active. The reload can be done through the API as well.

POST to the URL https://{{ip}}/api/node/mo/topology/pod-1/node-111/sys/action.json

With the following Body

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{
  "actionLSubj": {
    "attributes": {
      "dn": "topology/pod-1/node-111/sys/action/lsubj-[topology/pod-1/node-111/sys/ch]"
    },
    "children": [
      {
        "eqptChReloadLTask": {
          "attributes": {
            "dn": "topology/pod-1/node-111/sys/action/lsubj-[topology/pod-1/node-111/sys/ch]/eqptChReloadLTask",
            "adminSt": "start"
          }
        }
      }
    ]
  }
}