Cisco ACI Fabric APIC Discovery

We are considering the 3 node APIC cluster as APIC1, APIC2 and APIC3. Here are the discovery steps of the APICs within the ACI fabric.

What is Cisco ACI APIC?
One of the important pillar of Cisco ACI is APIC which is known as Cisco Application Policy Infrastructure Controller. 

It is single pane of glass for automation and management for the Cisco ACI fabric, policy enforcement, and health monitoring. It also optimizes performance and manages and operates a scalable multitenant Cisco ACI fabric.

Fig 1.1- Cisco ACI Fabric 

Step 1: Sending LLDP through its fabric ports will start by APIC1. The LLDP packets provide unique TLVs that include details on the infra VLAN and its function as an APIC (also referred to as the controller).

Step 2: When the leaf switch receives these LLDP packets from APIC1, it configures the infra VLAN on all of the ports where an APIC is found. The leaf begins transmitting DHCP Discovers to that infra VLAN.

Step 3: The user connects to APIC1's OOB IP(Out of Band IP) through HTTPS and registers the first leaf node in the Fabric Membership submenu.

Fig 1.2- Cisco ACI Fabric 

Step 4: APIC1 will respond with an IP address from the defined TEP address pool once the leaf has been assigned a Node ID, and the DHCP procedure will be completed.

Step 5: The registered leaf forwards DHCP Discovers to the APIC1 from additional directly linked spines detected through LLDP.

Step 6: The dynamically identified spines will display in the Fabric Membership submenu, where the user may register them.

Step 7: When the spines are registered, the APIC1 responds with an IP address from the TEP pool, and DHCP for those nodes is completed.

Step 8: The spines relay DHCP Discovers from all of pod1's nodes which the use of a full-mesh between spines and leaf switches

Step 9: Once the leaf nodes connected to the other APICs have been registered, the APIC cluster may be created using TCP communication. Make careful to finish the APIC2 and APIC3 configuration dialogues.

Step 10: Confirm that all APICs have formed a cluster and are properly fitted. If this is the case, fabric discovery is complete.

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