BFD (Bidirectional Forwarding Detection) in ACI

BFD (Bidirectional Forwarding Detection) is a network protocol designed to detect faults in the forwarding path between two connected devices. It provides rapid failure detection by continuously sending and receiving control packets between endpoints, ensuring that both devices can confirm their connectivity.

BFD operates independently of the physical medium, layer protocols, and routing mechanisms, making it a versatile tool for enhancing network reliability.

In Cisco ACI (Application Centric Infrastructure), BFD is used to monitor link or path liveliness between leaf and spine switches, endpoints, or other network devices, providing sub-second fault detection for both Layer 2 and Layer 3 connections.

Use Cases in Cisco ACI

• Monitoring Spine-to-Leaf Connections

  • Quickly detects failures in critical ACI fabric links.

• Enhancing Routing Protocols

  • Works with OSPF, BGP, and static routes for faster convergence during failures.

• Application Availability

  • Prevents downtime by rerouting traffic if the network encounters problems.

Configuration for Fabric BFD

Step 1: Enable Global Fabric BFD

1. Navigate : Fabric → Fabric Policies → Policies → Interface → L3 Interface → default

2. Enable BFD ISIS Policy configuration.

On a spine or leaf, verify neighbours:

Spine/Leaf# show bfd neighbors vrf overlay-1

Step 2: Modify Global BFD Timer

1. Go to Fabric → Access Policies → Policies → Switch → BFD → BFD IPv4

2. Create or edit a BFD policy with your desired timers.

Check neighbour details

Spine/Leaf# show bfd ipv4 neighbors details

Enable Interface-level Fabric BFD

Important: Disable the global BFD setting first.

1. Go toFabric → Fabric Policies → Policies → Interface → L3 Interface → default

2. Disable BFD ISIS Policy configuration.

3. Create a new L3 interface policy (for example, NP) and enable BFD ISIS Policy configuration there.

   • Fabric → Fabric Policies → Policies → Interface → L3 Interface → create “NP”

4. Assign your new L3 Interface Policy (NP) to the appropriate Policy Groups.

   • Leaf Interface Policy Group

     1. Fabric → Fabric Policies → Interfaces → Leaf Interfaces → Policy Groups

     2. Create a new policy group (for example, LNPG) and attach the NP L3 interface policy.

   • Spine Interface Policy Group

     1. Fabric → Fabric Policies → Interfaces → Leaf Interfaces → Policy Groups

     2. Create a new policy group (for example, SNPG) and attach the NP L3 interface policy.

5. Associate the Policy Groups with the correct Interface Profiles:

   • Leaf Interface Profile

     1. Fabric → Fabric Policies → Interfaces → Leaf Interfaces → Profiles

     2. Create a new profile and attach the LNPG policy group.

   • Spine Interface Profile

     1. Fabric → Fabric Policies → Interfaces → Spine Interfaces → Profiles

     2. Create a new profile and attach the SNPG policy group.

6. Confirm that the relevant switch profiles use LNPG and SNPG so that Fabric BFD is enabled on those interfaces.