Technical Documentation
Understanding Interconnect Devices
Interconnect devices in a QFabric switch provide a way for the Node devices to connect with one another over a high-speed backplane. By understanding the role of Interconnect devices, you can harness the benefits of low latency, superb scalability, and minimum packet processing offered by a single-tier data center architecture.
This topic covers:
Interconnect Device Introduction
Interconnect devices act as the primary fabric for data plane traffic traversing the QFabric switch between Node devices. The main task for the Interconnect devices is to transfer traffic between the Node devices as quickly as possible across a high-speed, available path backplane. To reduce latency to a minimum, the Interconnect device implements multistage Clos switching to provide nonblocking connections between any of the Node devices in the system. Figure 1 shows an example of how Clos switching works in an Interconnect device.
Figure 1: Clos Switching for Interconnect Devices
Traffic enters a QSFP+ port from a Node device, and an ingress chipset provides stage F1 processing. For the F2 stage, the frame is sent to a rear card and processed by a midplane chipset. Lastly, an egress chipset on the front card QSFP+ port handles processing tasks for the F3 stage. At each of the three Clos stages, a switching table chooses the best path and determines where to send the frame to reach the next stage. The F1 and F3 stages can be handled by the same front card or different front cards, depending on the best path selected by the fabric. After the frame traverses the Interconnect backplane, the Interconnect device sends the frame to the egress Node device.
QFX3008 Interconnect Devices
The QFX3008 Interconnect device contains eight slots in the front of the chassis. In each slot, you can install a front card containing 16 40-Gbps quad, small-form factor pluggable plus (QSFP+) ports. A fully configured system offers a total capacity of 128 QSFP+ connections. These front card ports attach to the high-speed backplane to reach the eight slots in the rear of the chassis, which provide the heavy-duty interconnections for the entire QFabric switch. In addition, four interfaces (two per Control Board) provide Gigabit Ethernet access to the control plane management network. Figure 2 shows an example of the data plane and control plane connections for a QFX3008 Interconnect device.
Figure 2: QFX3008 Data Plane and Control Plane Connections
