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vPC as DCI for Cisco ACI Spine-Leaf Architecture

Today I am going to take you through the Cisco ACI where I am going to talk about the vPC as a datacenter interconnection transport. We have various method to connect the two different datacenter with Inter-pod network or with back to back connectivity on the leaves. Some of you already knew as i discussed that in my earlier articles. If you want to have a look on the previous articles, please go through the below mentioned link which helps you to understand Cisco ACI as Spine-Leaf architecture model.

Hope the above mentioned articles helps you to understand the various deployment methods in Cisco ACI connecting to different datacenter across the globe using the single pod, multi-pod or multi-site environment.

There are some questions asked how we can have the L3out in the Cisco ACI environment towards the MPLS or internet kind of environment. I will come up with the concept of L3out in Cisco ACI environment by edge leaves or by GOLF routers but at this point of time i would like to talk about vPC in DCI transport.

vPC as DCI Transport
This is interesting, Here in the case of we are using vPC as a DCI transport, one pair of border leaf nodes can use a back-to-back vPC connection to extend Layer 2 and Layer 3 connectivity across sites. Unlike traditional vPC deployments on Cisco Nexus platforms, with Cisco ACI you don’t need to create a vPC peer link or a peer-keepalive link between the border leaf nodes. Instead, those peerings are established through the fabric.

You can use any number of links to form the back-to-back vPC, but for redundancy reasons, two is the minimum, and this is the number validated by cisco in their document.

Fig 1.1- vPC as DCI in ACI environment

This dual-link vPC can use dark fiber. It can also use DWDM, but only if the DWDM transport offers high quality of service. Because the transport in this case is ensured by Link Aggregation Control Protocol (LACP), you should not rely on a link that offers only three 9s (99.9 percent) or less resiliency. In general, private DWDM with high availability is good enough.

When using DWDM, you need to keep in mind that loss of signal is not reported. With DWDM, one side may stay up while the other side is down. Cisco ACI allows you to configure Fast LACP to detect such a condition, and the design reported in this document validates this capability to achieve fast convergence.