Introduction
A Cisco Nexus Virtual Port Channel (vPC) is a technology that allows the creation of a virtual link between two Cisco Nexus switches, typically in a data center environment. vPC enables these switches to appear as a single, logical device to connected devices, such as servers or other switches, while still maintaining separate physical connections to each switch.
Description
Dual-Attached End Devices: In a vPC setup, end devices (such as servers or switches) are dual-attached to both Nexus switches. This dual attachment provides redundancy and ensures that if one Nexus switch fails, the other can seamlessly take over to maintain connectivity.
vPC Peer Link: The vPC Peer Link is a dedicated link between the two Nexus switches used for synchronizing control plane information. It facilitates communication between the switches for tasks like exchanging state information, keeping track of vPC member ports, and ensuring consistency in the network.
vPC Member Ports: These are the individual physical ports on each Nexus switch that form the vPC. These ports are connected to the same downstream device, enabling load balancing and redundancy.
vPC Keepalive Link: The vPC Keepalive Link is an additional link used to monitor the health of the peer switch. The keepalive link ensures that each Nexus switch is aware of the operational status of the other, allowing for faster detection and recovery in case of a failure.
Role of vPC in STP (Spanning Tree Protocol) Avoidance: Traditional STP can lead to suboptimal use of network resources by blocking redundant links. vPC helps eliminate the need for STP blocking on the vPC member ports, allowing both Nexus switches to actively forward traffic.
Graceful Handling of Split Brain Scenario: A split brain scenario occurs when the vPC peer link is lost, and each Nexus switch believes it is the sole active switch. vPC is designed to handle this scenario gracefully to prevent network disruptions. The switch with higher priority or a designated primary switch will continue to operate, while the other switch suspends its vPC member ports.
Enhanced vPC (EvPC): Enhanced vPC (EvPC) extends the capabilities of vPC and supports features such as Layer 2 extension across geographically dispersed data centers. Technologies like Overlay Transport Virtualization (OTV) or VXLAN may be used in conjunction with EvPC for this purpose.
vPC+ (vPC Plus): vPC+ is an evolution of vPC that introduces additional features, such as support for FabricPath, a Cisco proprietary Layer 2 routing protocol.
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