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14 January 2019

Cisco Nexus vPC



When we are going to deploy a new Data Center network, we always have to think about the best network performance. If switches don’t have high rate interfaces, such as 100 Gbps interfaces, we should use more than one interface to get better performance. In addition, it’s a good idea to design the Data Center network with more than one uplink interface for redundancy because we’ll get better availability. Therefore, as network engineers, we should always design networks with several uplink interfaces for getting high performance and availability.

The best known technology for combining multiple network connections in parallel in order to increase throughput beyond what a single connection could sustain, and to provide redundancy in case one of the links fail is the Link Aggregation Control Protocol (LACP). However, there are already proprietary aggregation schemes similar to LACP. For example, the virtual Port Channel (vPC) is a Cisco technology which allow us to aggregate several port links between different Cisco Nexus switches to connect to a third party device (server, firewall, load balancer, etc) that supports link aggregation technology (LACP).

vPC Deployment Concept

Link Aggregation, such as vPC, has lots of technical benefits. One of the best technical benefit is the loop-free topology because it eliminates Spanning Tree Protocol (STP) blocked ports. In addition, we can use all available uplink interfaces, thus all available bandwidth is used, because we can send traffic for several interfaces at the same time. Theses technical benefits also simplify the network design. What’s more, Cisco vPC can be configured in different Cisco Nexus switches, accordingly, there are independent control planes.

If we are going to configure Cisco vPC, we’ll previously have to know the vPC architecture components. For instance, each Cisco Nexus switch will be a vPC Peer into the vPC domain. We also have to configure the vPC Peer Link and the vPC Peer Keepalive Link for the synchronization between vPC peer devices, which are synchronized thanks to Cisco Fabric Services (CFS) over the Ethernet protocol. In addition, there will be orphan ports for orphan devices and vPC member ports for aggregated switches.

vPC Architecture Components

I would like to highlight the role of the vPC Peer Link and the vPC Peer Keepalive Link. The vPC Peer Link is the most important component, which gives us the illusion of a single control plane, while the vPC Peer Keepalive Link is a Layer 3 backup test used to verify both Peers are alive. Therefore, if vPC Peer link fails and there is no Layer 3 communication, there will be a split brain scenario and a network outage.

Finally, some of you, maybe, are thinking about the Virtual Switching System (VSS) introduced by Cisco in Catalyst switches, or any other Multi-Chassis Link Aggregation technology built by other manufacturers, but vPC is slightly different with regard to the control plane. Cisco Nexus vPC maintains independent control planes.

Comparing Catalyst VSS with Nexus vPC
 
If you are interested in Cisco Nexus vPC and you need more information, you should check The Complete Cisco Nexus vPC Guide by Firewall.cx.

Do you usually configure LACP in your Data Center?

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