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ACI Fabric Discovery

ACI Fabric Discovery

Cisco ACI Fabric Bring-Up

1. Prerequisites2. Initial APIC Setup3. Fabric Discovery Process4. IS-IS Formation (Automatic)5. APIC Cluster Formation6. Key Protocols7. Verification Commands8. End-to-End Flow

1. Prerequisites

Physical Topology Rules

✓ Allowed

Leaf → Spine, APIC → Leaf, Leaf → Spine + Data Links

✗ Not Allowed

Leaf → Leaf, Spine → Spine

  • •Same firmware version on APICs and all switches
  • •APICs must be connected to different Leafs (dual-homed)
  • •Initial setup script must be completed on APICs

2. Initial APIC Setup

Fabric Info

Fabric Name, Fabric ID, Number of APICs, POD ID, Controller ID/Name

Infrastructure

TEP Pool: 10.0.0.0/16, Infra VLAN: 4093, BD Multicast: 225.0.0.0/15

OOB Management

OOB Mgmt IP: 192.168.10.1/24, GW: 192.168.10.254

Admin Config

Admin Password

3. Fabric Discovery Process

  • •Step 1: APIC discovers first Leaf (LLDP)
  • •Step 2: Leaf requests TEP IP (DHCP from APIC)
  • •Step 3: TEP assigned, Leaf becomes ACTIVE
  • •Step 4: Leaf discovers Spine (LLDP)
  • •Step 5: Manual Leaf registration (Node ID, Name, POD)
  • •Step 6: Spine requests TEP via Leaf DHCP relay

4. IS-IS Formation (Automatic)

Once all nodes have TEP IPs, APIC automatically enables IS-IS (Level-2) on all switches. Adjacencies form over the Infra VLAN.

  • •Underlay routing
  • •TEP reachability
  • •APIC communication

5. APIC Cluster Formation

  • •APIC-2/3 connects to Leaf via LLDP
  • •Leaf validates Appliance Vector (AV)
  • •If AV matches, APIC joins
  • •APICs sync database and policies
  • •Status → "Fully Fit"

6. Key Protocols

ProtocolPurpose
LLDPNeighbor Discovery
DHCPTEP IP Assignment
IS-ISUnderlay Routing
TCP/SSLPolicy Communication
VXLANOverlay Tunneling

7. Verification Commands

acidiag fnvread
POD  NODE  TYPE   IP          STATUS
1    1     apic   10.0.0.1    active
1    101   leaf   10.0.0.101  active
1    201   spine  10.0.0.201  active
acidiag avread
Fabric Name: ACI Fabric1
Fabric ID:   1
Cluster Size: 3
Status: Fully Fit

8. End-to-End Flow

  • •Configure APIC-1 (Setup Wizard)
  • •APIC discovers first Leaf (LLDP)
  • •Leaf requests TEP (DHCP)
  • •Register Leaf, assign TEP
  • •Leaf discovers Spine (LLDP)
  • •Spine requests TEP (via Leaf DHCP relay)
  • •Register Spine, assign TEP
  • •All nodes get TEPs
  • •IS-IS adjacency forms
  • •APIC-2 and APIC-3 join cluster
  • •Fabric becomes fully operational
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