The core layer is technologies used in the campus network or the enterprise network. The core layer is the part of the backbone that connects the different BNs together, often from building to building. This is the part of the backbone that contains the "TCP/IP gateways" described in next topic. The distribution layer is the part of the backbone that connects the LANs together. Although the access layer is not part of the BN, the technologies used in the LANs (or access layer) can have major impacts on the design of the backbone.įigure s.5 Backbone network design layers. The layer closest to the users is the access layer, the technology used in the LANs attached to the BN as described in the previous topic (e.g., 100Base-T, wireless Ethernet) (Figure 8.5). Network designers often think about three distinct technology layers1 when they design BNs. Before we discuss these architectures, we first must discuss the way in which network designers think about backbone designs and how to combine them that is, the different layers of backbones that exist in most organizations today. These architectures are mixed and matched to build sets of BNs. These architectures are routed backbones (routers that move packets on the basis of network layer addresses), switched backbones (switches that move packets based on data link layer addresses), and virtual LANs (switches that move packets through LANs that are built virtually, not using physical location). While there are an infinite number of ways in which network designers can build backbone networks, there are really only three fundamental architectures that can be combined in different ways. The bars in the diagram represent groups of network devices which provide redundancy and high bandwidth connectivity.The backbone architecture refers to the way in which the backbone interconnects the networks attached to it and how it manages the way in which packets from one network move through the backbone to other networks. The following diagram demonstrates that the datacenter network is constructed by different tiers of network devices. All paths between different tiers are active to provide high redundancy and bandwidth using Equal-Cost Multi-Path (ECMP) Routing. On the control plane, all network devices are running as OSI model Layer 3 routing mode, which eliminates the historical issue of traffic loop. These devices are strategically located in different physical locations with separate power and cooling domain to reduce impact of an environment event. The network is constructed using a large number of commodity devices to reduce the impact caused by individual hardware failure. The datacenter network is a modified version of a Clos network, providing high bi-sectional bandwidth for cloud scale traffic. Let’s illustrate the resiliency design principle using datacenter network. The redundancy is designed and built into the network from the physical aspect all the way up to control protocol. The above network components are designed to provide maximum availability to support always-on, always-available cloud business.
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