This is particularly so if most of the services these users wish to access are multiple backbone hops away from their own location. If there is a growth in the bandwidth needs of the users who are local to one node of the backbone, that growth can potentially affect multiple backbone links. The prime disadvantage of a distributed backbone is that the backbone links are shared by users and services located right around the network. In this case, the effects of any loop-induced storms or link flapping are isolated to that local region and not propagated further into the network.ĭisadvantages Backbone links are shared by many users This is particularly so if the backbone nodes perform Layer 3 routing between their local users and the backbone. The distributed backbone also segments the network, which can be advantageous in localizing the impact of network problems and aiding in the troubleshooting of those problems. In the ring topology, even the failure of a backbone node will only disrupt the users and services connected to that node–all other users will still be able to access all other services. If the backbone is in the form of a ring, then the failure of a single link in the ring does not cut users off from services, as their traffic will still have an alternative path to reach any location within the network. This is particularly true if services and resources are distributed around the nodes. The primary advantage of a distributed backbone is that it can reduce the impact of the failure of any given node. Thus, the links within the backbone carry traffic to and from destinations throughout the network, not simply to and from destinations that are local to the nodes at each end of the link.Ī distributed backbone design is especially suited to physically spread out environments, for example a campus network that connects distinct departments into a unified network. In either case, traffic from the users local to each node enters the backbone via that node, and at least some of the traffic traverses through other backbone nodes to reach its destination. In other cases, the servers are all located at a single node at the ‘head end’ of the distributed backbone. In some cases, there may be servers connected locally to most of the backbone nodes. The standard model of a distributed backbone network consists of a core ring of routing/switching nodes, each of which is the hub of its own local star network or its own local ring, which then extends out to a local access layer. To understand how such a design works, it is necessary to first consider some of the characteristics of these two designs, to understand their benefits and downsides, and to understand the environments to which each is most suited. This combined design is called a distributed collapsed backbone. This white paper discusses how to create a network design that combines both distributed and collapsed backbones. However, there are some network environments which could utilize the benefits of both options combined–particularly if they could avoid the disadvantages of both options. In medium to large networks, this central device is a chassis switch.Įach of these two designs has its advantages and disadvantages, and some environments are better suited to one design in particular. Network backbones come in two broad varieties: “distributed” and “collapsed”.Ī distributed backbone has a core consisting of multiple switches or routers chained together, typically in a ring.Ī collapsed backbone has a central device at the hub of a star network.
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