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Introduction to Cisco ACI stretched fabric and ACI Multi-pod Fabric Designs

Today I am going to talk about Cisco ACI where Cisco is providing two different solutions on Cisco ACI. One solution is Cisco ACI Multi-pod and other solution is named as Cisco ACI Multi-Site design or architecture. 

 Earlier Cisco ACI multi-pod environment we were doing the ACI stretched Fabric design but then Cisco come up with the solution called as Cisco ACI multi-pod.

 What is Cisco ACI Multi-pod ?
Well ACI multi-pod is a kind of ACI stretched Fabric design with more benefits and features. In simple words we can say that ACI multi-pod is a multiple ACI fabrics that is under control of single management or administration. 

 What is the key difference of ACI stretched fabric design and ACI multi-pod ?
Let's talk about the ACI stretched fabric design, Let us suppose we have two ACI fabric design where we have Spine-Leaf architecture. One is ACI-I and other is ACI-II, if you are going to connect the leaf switches of ACI-I with the spine switches of ACI-II and leaf switches of ACI-II with spine switches of ACI-I makes ACI Stretched fabric design. Below diagram shows the best way of Cisco ACI stretched fabric design between three ACI fabric networks.

Fig 1.1- Cisco ACI Stretched Fabric Solution with Cisco APIC
So now let's talk about the Cisco ACI multi-pod, Cisco did the enhancement for the connection of the different ACI fabric network, they introduce IPN which is called as Inter-pod network between the ACI fabric network. All the ACI fabric network connected to each other via inter-pod network. Cisco created IPN can be any type of transport that supports IP Routing and Multicast. There are however a number of design considerations to consider when deploying ACI along with the IPN Network. 

 Below design showing the ACI-multipod design where Cisco introduces inter-pod network to have a communication between ACI fabric networks and is under one single administration.
Fig 1.2- Cisco ACI multi-pod fabric design
So from both the design you can easily came to know about the difference and the enhancements of the ACI multi-pod design.
ACI Multi-Pod was utilised to create a single ACI Fabric made up of the three Data Centre locations. The IPN network was comprised of a 100Gb Dark Fibre Network with Nexus 9Ks providing the IPN termination.

Having a Multi-Pod ACI solution allowed the customer to manage all their Data Centres as one, easily deploy policy across the entire network and route traffic as efficiently as possible from one site to another. When deploying Multi-Pod, a BGP EVPN full-mesh is created between the Spine and Leaf switches creating a more efficient overlay.

What is the advantages of ACI multi-pod over the ACI stretched fabric ?
Advantages of an ACI Multi-Pod solution: multiple pods managed as a single administrative domain, Active/Active Data Centre deployment, workload mobility domains extended and end-to-end policy enforcement. So you have a resiliency in your ACI multi-pod design over the ACI stretched fabric network designs.

What will be the Scalability of the Cisco ACI Multi-pod Fabric designs ?
 So yes, this is one of the main point which enterprises looking to deploy the Cisco ACI Multi-site fabric design. Below are some points for ACI Multi-Pod fabric network design scalability 
  • Maximum number of Pods: 4
  • Maximum number of Leaf nodes across all Pods: 300 (deploying a 5 nodes APIC cluster)
  • Maximum number of Leaf nodes across all Pods: 80 (when deploying a 3 nodes APIC cluster)
  • Maximum number of Leaf nodes per Pod: 200 (when deploying a 5 nodes APIC cluster)
  • Maximum number of Spine nodes per Pod: 6
What are the basic solutions in the Cisco ACI Multi-pod APIC clusters ?
Cisco have two different solutions in the Cisco ACI Multi-pod
  • Single APIC clusters: In single APIC controller cluster representing the single point of management and policy definition for the entire network, independently from the number of separate ACI fabrics (Pods) compounding it.
  • Multiple APIC clusters: The other deployment options is to characterised by having an independent APIC cluster managing each interconnected ACI network.
IPN Multicast Support
The use of VXLAN as overlay technology allows providing Layer 2 connectivity services between endpoints that may be deployed across Layer 3 network domains. Those endpoints must be able of sending and receiving Layer 2 multi-destination frames (BUM traffic), as they are logically part of the same Layer 2 domain. BUM traffic can be exchanged across Layer 3 network boundaries by encapsulating it into VXLAN packets addressed to a multicast group, so to leverage the network for traffic replication services.

This is the basic article to understand the Cisco ACI stretched fabric and ACI Multi-pod Fabric Designs. I will come up with the traffic flow, Issues in BUM traffic across pods and other split brain scenarios in the Multi-pod environments. I hope you got the basic ideas of Cisco ACI design considerations.