This article described the following topics: what is hierarchical network design, typical layers in hierarchical network design, hierarchical network topologies, hierarchical network design benefits, and implementation considerations.
Hierarchical network design
A hierarchical network design is a systematic way of structuring a network into various levels, each with defined functions, to better manageability, scalability, and performance. Since its first proposal by Cisco in 2002, this design paradigm has grown to become a standard technique for building dependable, scalable, and reasonably priced networks. A hierarchical structure separates the network into manageable blocks that restrict local traffic to stay local, in contrast to earlier flat network designs that had trouble with broadcast management and traffic filtering as they grew.
Network size and requirements, which are essential for successful implementation, influence the network architecture. It integrates concepts like flexibility, modularity, resilience, and hierarchy.
Hierarchy: Because it breaks up the intricate network of devices into smaller, more manageable sections, hierarchy is a straightforward yet powerful tool for network architecture.
Modularity: A network that has a high degree of modularity has numerous modules for different functions, which facilitates network design and implementation.
Resiliency: Simply said, resilience refers to the network’s ability to withstand both anticipated and unforeseen events. Expected circumstances could include regular daily traffic patterns or planned repairs and Unexpected events might include network attacks, hardware or software malfunctions, and anomalous traffic flows (more than anticipated).
Flexibility: This refers to the network’s capacity to grow or adapt in response to demands and specifications without significantly altering the network’s architecture.
Also Read About What Is Repeater In Networking, How It Works And Advantages
Typical Layers in Hierarchical Network Design
Three logical levels are commonly seen in a hierarchical LAN design, and they frequently correspond to the network’s physical configuration:
Core Layer
- Often referred to as the network backbone, this layer is in charge of swiftly sending enormous volumes of data.
- Its primary objective is to offer dependable transport and fast, highly redundant forwarding services between distribution-layer equipment.
- To guarantee maximum throughput and reduce failure risk, the core layer should be as lean and straightforward as possible, avoiding complicated policies, packet modification (such as restrictive ACLs or QoS categorisation), and features.
- It links devices at the distribution layer and is usually composed of expensive switches and routers with redundant connections.
- It combines distribution switches in a big campus LAN.
Distribution Layer
- The aggregation layer, sometimes referred to as the “Workgroup layer,” serves as a link between the core and the access layer.
- Its main function is to distribute traffic to the rest of the network by aggregating it from various access layer switches.
- It implements policy-based connectivity, which includes quality of service (QoS), filtering, and security restrictions (such access control lists).
- It defines broadcast and multicast domains and manages VLAN routing.
- Redundancy and load balancing are provided by this layer, which also aids in the creation of “distribution blocks” that confine issues to a particular network segment and stop them from impacting the entire system.
- The distribution layer, which chooses the fastest path to network service requests, frequently comprises of routers and multi-layer switches.
Access Layer
- This is where end-user equipment, such as servers, wireless access points (APs), IP phones, printers, and PCs, connect to the network directly.
- It serves as the network’s “edge” and offers high-bandwidth connectivity. Layer 2 switching capabilities, access control, collision domain definition, and port security implementation are important features.
- It is the first line of defence for security and frequently uses network control protocols, policing, queuing, and QoS marking.
- The access layer must allow for specialized access for devices utilising cutting-edge technologies like speech and video, as well as bursts of high-bandwidth traffic for everyday operations.
Also Read About What are Network Bridges? Advantages of Bridge in Networking
Hierarchical Network Topologies
Although a three-layer architecture is typical, networks can be built with fewer physical layers.
Three-Tier Campus Design
- The access, distribution, and core layers are completely isolated in this design.
- Because it offers the best performance, scalability, and network availability, it is usually utilized for bigger LAN setups or campus networks with several buildings.
- When networks expand beyond three distribution layers in one place, a core layer is taken into consideration. It streamlines the topology by having each pair of distribution switches fully meshed to the core, rather than all distribution switches fully meshed to each other.
Collapsed Core, a two-tiered campus design
- In this architecture, the core layer and distribution layer functions are combined into a single layer/device.
- It is more cost-effective and usually utilised for single-campus setups or smaller businesses that cannot afford the price of individual core devices.
- The distribution switches assume the core layer’s responsibilities in a collapsed core, usually by being completely meshed with one another if there aren’t many distribution blocks.
- Although it is less expensive, it nevertheless provides the majority of the advantagesnd services of a three-tier network.
For campus LANs, Cisco Software-Defined Access (SDA) employs a software-defined networking strategy.
- The SDA architecture communicates with the network infrastructure, also known as the fabric, through APIs and a controller (such as Cisco DNA Centre).
- The fabric is separated into an overlay, which is where SDN controller services are tunnelled, and an underlay, which is the actual network in charge of forwarding.
- SDA can be constructed with new hardware, where DNA Centre can automatically setup underlay features, or with two-tier or three-tier campus networks that are already in place.
- Each access switch must be connected to two distribution layer switches, but not to other access switches, according to the conventional campus LAN Layer 2 design. A greenfield SDA fabric, on the other hand, employs a routed access layer design, which means that every LAN switch is a Layer 3 switch with routing turned on. The underlay is configured with consistent parameters by DNA Centre.
WAN Topologies and Hierarchical Design
- WANs (Wide Area Networks) often connect geographically dispersed Local area networks(LANs).
- Regional hubs can form a core network in a two-layer hierarchical WAN design concept.
- WANs frequently make use of carrier services and serial connections. WANs can also contact the WAN core layer via other technologies, such as ISDN and Frame Relay.
Data Center Topologies (Spine-Leaf)
- Top of Rack (ToR) switches, which serve as the access layer, are frequently connected to End of Row (EoR) switches, which serve as the distribution layer, in traditional data centre cabling to provide redundant pathways.
- Cisco Application Centric Infrastructure (ACI) uses a unique physical switch topology called spine and leaf, also known as a Clos network.
- Every spine switch is connected to every leaf switch, and every leaf switch is connected to every spine switch in a spine-leaf configuration.
- Servers, virtual machines, containers, and routers are examples of endpoints that only connect to leaf switchenever to spine switches.
- This architecture ensures all switches are a single hop distant from each other and is extremely scalable.
- In software-defined networking (SDN), the underlay is usually implemented using the spine-leaf architecture.
Hierarchical Network Design Benefits
There are many benefits to hierarchical network designs:
Design Simplicity
Because connections and equipment typically align with an organization’s logical structure, networks are easier to design and implement. Localising changes to particular layers facilitates initial setup and logical modifications.
Improved Performance
Less dependence on subpar intermediary switches is achieved by routing data across aggregated switch-port lines at almost wire-rate. Data may travel nearly wire-speed for the majority of its route because to high-performance switches at the distribution and core layers, which also lead to higher speeds and fewer bandwidth problems.
Increased Cost-Effectiveness
Businesses can save money by only buying the equipment that is required based on their logical structure. The modular design enables for network expansion without major one-time expenses.
Scalability
Because hierarchical networks are modular, they scale remarkably well, enabling the replication of design elements as the network expands. Because of this, growth is easy to plan and execute, enabling the gradual addition of access, distribution, and core layer changes as required.
Security
Security is improved and easier to maintain. At the distribution layer, which is where Layer 3 data processing is usually done, more sophisticated security measures, such access control rules based on communication protocols, can be put in place. At the access layer, several port security settings can be established.
Easier to Manage
Management is made simpler by the different activities that each layer completes. Configurations can be copied to simply deploy new switches, and changes can be propagated across consistent levels (e.g., all access layer switches). Additionally, this makes debugging simple and recovery rapid.
Improved Fault Isolation
Fault isolation is enhanced by segmenting the network into small, straightforward parts. Finding issue places is made easier by network management’s ability to swiftly identify transition points. For instance, issues in a single distribution block are specific to that block and have no impact on the network as a whole.
Modular Network Growth
As the network grows, modularity enables repeatable design elements, reducing the expense and difficulty of upgrading specific network segments.
Redundancy
Network availability is significantly increased by straightforward redundancy deployments. Distribution layer switches can connect to two or more core layer switches, while access layer switches can link to two different distribution layer switches for path redundancy. An access layer switch failure primarily impacts the devices linked to it, not the network as a whole, even when end nodes at the access layer have little redundancy.
Maintainability
Compared to alternative topologies, the modular and scalable design makes network administration easier.
Also Read About Network Switching: How Switches Connect For Device Networks
Considerations for Implementation
Notwithstanding its advantages, hierarchical design necessitates a number of factors:
- Business Needs: The design should take into account the bandwidth, security, and application-specific requirements of the organisation, both now and in the future.
- Budgetary Restrictions: Because numerous layers of switches and routers are required, initial setup may be more costly. Nonetheless, the modular design enables cost-spreading development in stages.
- Network Size: For very small networks (e.g., less than 200 devices), a three-tier design might be overkill and introduce extra complexity; a collapsed-core (two-tier) design might be more appropriate and cost-effective. A complete three-tier design will be necessary for larger networks.
- On-premises vs. Cloud Services: How users access network services may have an impact on the hierarchical architecture decision. Traffic mainly exits the network if the majority of services are cloud-based, which could lessen the importance of specific distribution and core layer speeds.
- Compliance: Local construction and electrical codes, as well as other legal requirements, may have an impact on network architecture.