Hierarchical network architecture, first put forth by Cisco in 2002, has now spread throughout the industry as a recommended practice for creating dependable, scalable, and affordable networks. Early networks were flat and could only be stretched in one direction using hubs and switches, making it difficult to filter unwanted traffic and manage broadcasts. Response times would worsen as a network expanded in size. It was necessary to create a new network design, which led to the hierarchical strategy. Even while flat network designs are still used today, they are typically used for very small networks or designs that aim to reduce costs by utilizing a minimal number of routers or switches. A network is divided into layers by a hierarchical structure, and each layer has a set of functions that specify how it fits into the overall network. This gives a network designer the ability to select the best hardware, software, and features to fulfill a specific purpose for that network layer. Additionally, data management is far more effective. Local traffic in a hierarchical design only goes to a higher tier when it is destined for another network.
Typical layers in Hierarchical Network Design:
There are three layers in Hierarchical Network Design that are as follows:
- Access: Manages user and workgroup access to network resources. This layer often includes Layer 2 switches and access points that connect workstations and servers. At this layer, you can handle access control and policy, define different collision domains, and implement port security.
- Distribution: Acts as a bridge between the access layer and the core. Its key functions include routing, filtering, and WAN access, as well as determining how packets can reach the core. This layer evaluates the quickest way to access network service requests – for example, how to transfer a file request to a server – and, if necessary, forwards the request to the core layer. This layer is often made up of routers and multi-layer switches.
- Core: Often known as the network backbone, this layer is in charge of quickly transmitting massive amounts of traffic. The core layer connects distribution layer devices and is typically made up of high-speed devices such as high-end routers and switches with redundant links.
Benefits of Hierarchical Network Design:
- Design Simplicity: As equipment and connections typically match the logical structure of an organization, hierarchical networks are among the simplest to design and implement. Routers and switches delimit various organizational units starting from a single or numerous points of traffic egress and ingress until the final end-user is left with a single Ethernet adapter or 802.11 Wi-Fi network access point. Segments of the network are clearly separated by organizational boundaries, enabling simple initial setup and logical adjustments should organizational network requirements alter.
- Better Performance: Data is routed through aggregated switch-port lines at the near-wire rate in a hierarchical network topology as opposed to being delivered through inferior intermediary switches. High-performance switches are used at the distribution and core layers, resulting in faster speeds and fewer network bandwidth problems. Therefore, during the majority of its journey within the network, data should flow at close to wire speed between every device if the network is configured properly.
- Improved cost-effectiveness: The necessary yet pricey IT networking equipment. However, because the business can only purchase the equipment that is actually required based on the logical structure of the enterprise, hierarchical network architecture might result in cost savings. Since the network is modular, it can be expanded without requiring substantial one-time expenses. One access switch and a few Ethernet connections, for instance, can frequently replace the need for a complete set of routers and switches when adding a new department (many of which will sit underused).
- Scalability: Hierarchical networks scale exceptionally well. The architecture’s modularity enables you to reproduce design pieces as the network grows. Because each module instance is constant, expansion is simple to design and implement. For example, if your design model includes two distribution layer switches for every ten access layer switch, you can keep adding access layer switches until you have ten access layer switches cross-connected to the two distribution layer switches before adding more distribution layer switches to the network topology. In addition, as more distribution layer switches are added to address the load from the access layer switches, additional core layer switches can be added to handle the increasing pressure on the core.
- Security: It is enhanced and more easily managed. Different port security settings that allow for control over which devices are permitted to connect to the network can be configured in access layer switches. Additionally, you have the choice to employ more complicated security procedures at the distribution layer. You can implement access control rules that specify the deployment of communication protocols on your network and the areas to which they are allowed to travel. For instance, you may implement a policy that limits HTTP traffic at the distribution layer if you want to restrict HTTP usage to a particular user community connected at the access layer. Your switches must be able to process policies at the upper layers in order to restrict traffic depending on protocols like IP and HTTP. Your switches must be able to handle policies at that layer in order to restrict traffic based on higher-layer protocols like IP and HTTP. Although certain access layer switches enable Layer 3 capability, Layer 3 data processing is often handled by distribution layer switches because of their superior processing capabilities.
- Easier to Manage: A hierarchical network is generally easy to manage. The hierarchical design’s layers each carry out particular tasks that are consistent throughout that layer. Since all access layer switches in the network presumably fulfill the same functions at their layer, if the functionality of an access layer switch needs to be changed, you could duplicate that change across all access layer switches in the network. The ability to copy switch configurations between devices with minimal change facilitates the deployment of new switches. Each layer’s switches must be consistent with one another for quick recovery and straightforward debugging. Device configuration inconsistencies may occur in some unique circumstances, thus you should make sure that settings are clearly documented so that you can compare them before deployment.
- Strengthened fault isolation: Fault isolation is improved by breaking the network down into small, simple components. Network management can quickly comprehend the network’s transition points, which aids in locating potential trouble spots.
- Modular Network Growth: Changes are facilitated by hierarchical architecture. When designing a network, modularity enables you to produce design features that you can duplicate as the network expands. The expense and complexity of upgrading the network are limited to a small portion of the entire network because every component of its architecture needs to be altered. Changes frequently affect a huge number of systems in big, flat network designs. Limited mesh topologies within a layer or component, like the campus core or backbone connecting central sites, retain utility even in hierarchical design models.
- Redundancy: The availability of a network becomes increasingly critical as it grows. Simple redundant implementations of hierarchical networks can greatly boost availability. To achieve path redundancy, access layer switches are linked to two distinct distribution layer switches. If one of the distribution layer switches fails, the access layer switch can switch to the other. Furthermore, distribution layer switches are linked to two or more core layer switches to assure path availability in the event that a core switch fails. The only layer with minimal redundancy is the access layer. End node devices, such as PCs, printers, and IP phones, do not often support multiple access layer switches for redundancy. If an access layer switch fails, just the devices linked to that single switch are affected. The rest of the network would continue to operate normally.
- Maintainability: Hierarchical networks are simple to manage since they are modular in design and scale up quickly. Other network topology choices make manageability more challenging as the network gets bigger. Additionally, there may be a finite size limit to the network’s expansion before it becomes too difficult and expensive to maintain, according to some network design models. The definition of switch functions at each tier in the hierarchical design model facilitates choosing the right switch. Another limitation may still exist at another layer even after adding switches to one layer. All switches must be high-performance switches in order for a full mesh network topology to operate at its peak efficiency since each switch must be able to handle every task on the network. Switch functions vary at each stage in the hierarchical architecture. Instead of spending more money on the distribution and core layer switches to achieve perfect network performance, you can save money by using less expensive access layer switches at the lowest layer.
- Performance: By reducing the transmission of data through intermediary switches with poor performance, communication performance is improved. From the access layer to the distribution layer, data is often transmitted at close to wire speed over aggregated switch port links. After that, the traffic is forwarded up to the core and routed there using the distribution layer’s high-performance switching capabilities. There is less competition for network capacity exists because the core and distribution layers operate at extremely fast rates. Hierarchical networks that are well-designed can therefore reach near-wire speed between all devices.
Conclusion:
Hierarchical topologies were the inspiration for today’s fast-converging protocols. Use modular hierarchical topologies using protocols like Open Shortest Path First that are developed with these controls in mind to reduce the impact of routing-protocol processing and bandwidth consumption (OSPF). Route summary is facilitated by hierarchical network design. Route summarizing has enormous benefits for EIGRP and all other routing technologies. Route summarizing lessens the routing-protocol processing required by the routers as well as the routing-protocol overhead on network links.