Help us improve your experience.

Let us know what you think.

Do you have time for a two-minute survey?


Virtual Chassis Fabric Introduction

VCF is a low-latency, high-performance fabric architecture that uses a spine and leaf topology to combine multiple devices into a resilient fabric architecture that is managed as a single device. VCF is optimized to support small and medium-sized data centers that contain a mix of 1-Gbps, 10-Gbps, and 40-Gbps Ethernet interfaces, with some VCF topologies also supporting 100-Gbps Ethernet connections.

VCF provides the following benefits:

  • Latency—VCF provides predictable low latency by using a fabric architecture that ensures each device is only one or two hops away from every other device in the fabric. The weighted algorithm that makes traffic-forwarding decisions in a VCF avoids congestion and intelligently forwards traffic over all paths within the VCF to any destination device, ensuring predictable low latency for all traffic traversing the VCF.

  • Resiliency—The VCF architecture provides a resilient framework because traffic has multiple paths across the fabric. Traffic is easily diverted to another path within the fabric when a device or link fails.

  • Flexibility—You can easily expand the size of your VCF by adding devices to the fabric as your networking needs grow.

  • Investment protection—In environments that need to expand because the capabilities of a QFX5110, QFX5100, QFX3600, QFX3500, or EX4300 Virtual Chassis are maximized, a VCF is often a logical upgrade option because it enables the system to evolve without having to remove the existing, previously purchased devices from the network.

  • Manageability—VCF provides multiple features that simplify configuration and management. VCF, for instance, has an autoprovisioning feature that enables you to plug and play devices into the fabric after minimal initial configuration. VCF leverages many of the existing configuration procedures from a Virtual Chassis, so that you can configure and maintain a VCF easily if you are already familiar with the procedures for configuring and maintaining a Virtual Chassis.

VCF evolved from Juniper’s Virtual Chassis technology, which allows you to interconnect multiple switches in a ring topology and manage the interconnected switches as a single device.

VCF inherited the following major architectural pillars from Virtual Chassis technology:

  • All member devices in a VCF are managed and controlled by a pair of switches acting in the Routing Engine (RE) role, allowing the entire VCF to be controlled as a single device running Junos OS.

  • A backplane is constructed over the Virtual Chassis port (VCP) links to allow the VCF to be managed as a single device running Junos OS.

  • The ports connecting member devices are VCPs controlled using the Virtual Chassis Control Protocol (VCCP). The VCCP daemon (VCCPd) runs on every member device in the VCF to discover and manage the VCF topology.

  • Many of the CLI commands used to create or maintain a Virtual Chassis are also used to create or maintain a VCF.

The following evolutions to the Virtual Chassis technology introduced by VCF include:

  • Support for a multi-path fabric architecture that has the intelligence to forward traffic over the shortest paths within the fabric.

  • Intelligent bandwidth allocation that detects and considers end-to-end bandwidth for all paths across the fabric when forwarding flows from one member switch in the fabric to another member switch in the VCF.

  • Ability to calculate multiple bidirectional multicast distribution trees and perform load balancing based on these trees.

For more detailed overview information on VCF, see Virtual Chassis Fabric Overview and Understanding Virtual Chassis Fabric Components.