Understanding vPC in
Cisco ACI: A Modern Approach to High Availability
In the evolving landscape of data center networking, Virtual Port Channel (vPC) stands out as a cornerstone of high availability and link redundancy. While traditional NX-OS environments rely on CLI-driven configurations, Cisco ACI reimagines vPC through a policy-driven, intent-based model that aligns with the fabric’s overarching design philosophy.
Unlike legacy setups, ACI abstracts physical connectivity into logical constructs, allowing administrators to define vPC behavior through interface policy groups, switch profiles, and attachable access entity profiles (AAEPs). This not only simplifies deployment but also ensures consistency across the fabric.
At its core, a vPC in ACI enables two leaf switches to present a unified uplink to a downstream device—be it a server, firewall, or load balancer—without relying on spanning tree protocols. The result is active-active forwarding, improved bandwidth utilization, and seamless failover.
In this guide, we’ll walk through the step-by-step configuration of vPC in Cisco ACI, demystifying each component and highlighting best practices to ensure a robust and scalable deployment.
Note:- In Cisco ACI, a Fabric Extender (FEX) can be integrated using a port channel in a straight-through topology, where each FEX connects directly to a leaf switch. While vPCs can be established between hosts and the FEX for redundancy and load balancing, the FEX itself does not support vPC connectivity to multiple leaf switches.
Complete
Steps to Create vPC in Cisco ACI (via APIC GUI)
Step 1: Leaf
Onboarding (One-by-One)
🔍 Monitor Discovery in APIC
- Log in to the APIC GUI
- Navigate to:
Fabric → Inventory → Fabric Membership → Nodes Pending Registration - Wait for Leaf101 to
appear
- You’ll see its Serial Number
- Node Role: Leaf
- Status: Blank / Not Registered
📝 Register Leaf101
- Right-click on Leaf101’s serial number
- Click Register
- In the registration window, enter:
- Node ID: 101
- Node Name: Leaf101
- Click Register
- Wait for it to appear in Registered
Nodes
📝 Register Leaf102
- Repeat the same steps for Leaf102:
- Wait for it to appear in Nodes
Pending Registration
- Right-click → Register
- Enter:
- Node ID: 102
- Node Name: Leaf102
- Click Register
- Wait for it to appear in Registered
Nodes
🔢 Step-by-Step ACI Configuration Flow
2. VLAN Pool (VLAN
113)
- Navigate to:
Fabric → Access Policies → Pools → Right Click on VLAN and click Create Vlan Pool - Create VLAN Pool:
- Name: VLAN_113_Pool
- Mode: Static
- Click + under Encap Blocks
Ø Range: 113 – 113
Ø Allocation mode: Static
- Click Ok - >Submit
3. Domain (Physical
Domain)
- Go to:
Fabric → Access Policies → Physical and External Domains ->Right Click on Physical domain -> - Create Physical Domain:
- Name: PhysDom_VLAN113
- VLAN Pool: VLAN_113_Pool
- Click Submit
4. AEP (Attachable
Access Entity Profile)
- Navigate to:
Fabric → Access Policies → Policies-> Global → Right Click on Attachable Access Entity Profiles -> Click Create Attachable Access Entity Profiles - Create AEP:
- Name: AEP_VLAN113
- Click + under Domains and Associated
Domain: PhysDom_VLAN113
- Click Update ->Next -> Finish
5. Interface Policy
Group (vPC)
- Go to:
Fabric → Access Policies → Interface → Leaf Interfaces - >Policy Groups->Right click on VPC Interfaces - >Create VPC Interfaces - Create VPC Interface Policy Group:
- Name: vPC_LF101_LF102_1_1
- AEP: AEP_VLAN113
- Port Channel Policy: system-lacp-Active
- Link Level Policy: system-link-level-XG-Auto
- Click Next > Finish
6. Create vPC
Policy (Your Mentioned Step)
- Go to:
Fabric → Access Policies → Policies → Switch - Right-click on Virtual Port
Channel Default
Name:VPC_101_102
ID:10
VPC Domain Policy: Default
Switch1: Leaf101
Switch2: Leaf102
This step ensures the
vPC behavior is defined at the switch policy level.
7. Interface
Profile
- Navigate to:
Fabric → Access Policies → Interface → Leaf Interface -> Profiles - Right click on the interface profile and
click Create Interface Profile:
- Name: IntProf_Leaf101_102
- Click + under Interface Selector:
- Name: Eth1_4
- Interface ID: 1/4
- Policy Group: vPC_LF101_LF102_1_1
- Click Ok - > Submit
8. Switch Profile
- Go to:
Fabric → Access Policies → Switches → Profiles - Right Click on Profile and click Create
Leaf Profile:
- Name: LeafProf_101_102
- Click + under Leaf Selector:
- Name: Leaf101_102
- Node Block: From 101 to 102
- Click Update -> Next
- Attach Interface Profile:
- IntProf_Leaf101_102
9. Create Tenant
- Navigate to:
Tenants - Click Add Tenant
- Name: Tenant_WebApp
- Click Submit
10. Create VRF
- Navigate to:
Tenants - Click Networking -> VRF -> Right
click on VRF -> click Create VRF
- Name: WebApp_VRF
- Uncheck Create A Bridge Domain
- Click Finish
11 Create BD
- Navigate to:
Tenants - Click Networking -> Bridge
Domain -> Right click on Bridge Domain-> click Create Bridge Domain
- Name: WebApp_BD
- VRF: WebApp_VRF
- Click Next
- Click + under Subnet
Ø Gateway IP: 10.1.1.1/24
Ø Check “Make this IP address Primary”
Ø Scope: check “Advertised Externally”
- Click OK -> Next->
Finish
12. Create
Application Profile (AP)
- Inside Tenant_WebApp, go to:
Application Profiles - Right Click on Application Profile and Create Application Profile:
- Name: WebApp_AP
- Click Submit
13. Create Endpoint
Group (EPG)
- Inside WebApp_AP, go to:
EPGs - Right Click on Application EPG and click
Create Application EPG:
- Name: WebApp_EPG
- Bridge Domain: WebApp_BD
- Click Finish
- Right Click on WebApp_EPG and click
ADD Physical Domain Association:
- Domain Association: PhysDom_VLAN113
- Click Submit
14. Create Contract
(Allow TCP Port 80)
- Go to:
Tenant_WebApp → Contracts -> Standard - Right Click on Standard -> Click Create
Contract:
- Name: Allow_HTTP
- Click + under Subject:
- Name: HTTP_Subject
- Filter: Click + under Filter
- Click + Under Name
- Name: HTTP_Filter
- Click + under Entries
- Name: HTTP_Entry
- EtherType: IP
- IP Protocol: TCP
- Destination Port: From http – To http
- Click Update-> Submit
- Click Update -> Ok -> Submit
- Provide contract to/from EPG as needed
15. Static Binding
of EPG to Port
- Go to Tenant WebApp_EPG->
Application Profiles -> WebApp_AP ->
Application EPGs -> WebApp_EPGs
- Right Click on WebApp_EPGs -> Click Deploy
Static EPG on PC,VPC, or Interface
- Path Type: Virtual Port Channel
- Path: Leaf101/eth1/4 and Leaf102/eth1/4
- Mode: Trunk
- Encapsulation: vlan-113
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