Cisco ACI Fabric Initialization

The discovery process for an ACI fabric, beginning with an overview of the actions that happen and the verification steps used to confirm that a functioning fabric exists. Troubleshooting issues where fabric nodes fail to join is quite easy.

In this discovery process, a fabric node is considered active when the APIC and node can exchange heartbeats through the Intra-Fabric Messaging (IFM) process. The IFM process is also used by the APIC to push policy to the fabric leaf nodes.

Fabric discovery Process is tri-stage process.

1. The leaf node directly connected to the APIC is discovered in the first stage.

2. Secondly discovery brings in the spines connected to that initial seed leaf.

3. Last stage is discovery of the other leaf nodes and APICs in the cluster.

LLDP (Link Layer Discovery Protocol), DHCP and TEP (Tunnel Endpoint) are the major components of discovery Process.

Inter-Fabric Messaging (IFM).  IFM uses SSL-encrypted TCP communication.  Each APIC and fabric node has 1024-bit SSL keys embedded in secure storage.

The discovery process states are shown in the Fabric Node Vector table.       States and descriptions:

• Unknown – Node discovered but no Node ID policy configured
• Undiscovered – Node ID configured but not yet discovered
• Discovering – Node discovered but IP not yet assigned
• Unsupported – Node is not a supported model
• Disabled – Node has been decommissioned
• Inactive – No IP connectivity
• Active – Node is active

Below is a description of each out-of-service issue that may be encountered:

• fabric-domain-mismatch – Adjacent node belongs to a different fabric
• APIC UUID mismatch
• Connection-mismatch – Invalid connection
• adjaceny-not-detected – No LLDP adjacency on fabric port

To verify LLDP information exchange, the command show lldp neighbors can be used from APIC. Before initiate the Fabric enable lldp is vital to proper discovery of each Switch.