Core Layer Functionality

Last Updated on Tue, 25 Jul 2023 | Network Design

This section describes core layer functions and the interaction of the core layer with the distribution layer.

The Role of the Core Layer

The function of the core layer is to provide fast and efficient data transport. Characteristics of the core layer include the following:

■ The core layer is a high-speed backbone that should be designed to switch packets as quickly as possible to optimize communication transport within the network.

■ Because the core is critical for connectivity, core layer devices are expected to provide a high level of availability and reliability. A fault-tolerant network design ensures that failures do not have a major impact on network connectivity. The core must be able to accommodate failures by rerouting traffic and responding quickly to changes in network topology. The core must provide a high level of redundancy. A full mesh is strongly suggested, and at least a well-connected partial mesh with multiple paths from each device is required.

■ The core layer should not perform any packet manipulation, such as checking access lists or filtering, which would slow down the switching of packets.

■ The core layer must be manageable.

■ The core devices must be able to implement scalable protocols and technologies, and provide alternative paths and load balancing.

Switching in the Core Layer

Layer 2 switching or multilayer switching (routing) can be used in the core layer. Because core devices are responsible for accommodating failures by rerouting traffic and responding quickly to network topology changes, and because performance for routing in the core with a multilayer switch incurs no cost, most implementations have multilayer switching in the core layer. The core layer can then more readily implement scalable protocols and technologies, and provide alternate paths and load balancing.

Figure 3-5 shows an example of Layer 2 switching in the campus core.

Figure 3-5 Layer 2 Switching in the Campus Core

Layer 2 Multilayer Layer 2

Figure 3-5 shows an example of Layer 2 switching in the campus core.

Layer 2 Multilayer Layer 2

Core Device Layer

Routing Protocol at the Distribution Layer Computes Primary and Alternative Paths

Redundant Layer 2 Links to Provide Resilience

Redundant Component to Avoid Network Outages in Case of a Device Failure

Routing Protocol at the Distribution Layer Computes Primary and Alternative Paths

Redundant Layer 2 Links to Provide Resilience

Redundant Component to Avoid Network Outages in Case of a Device Failure

Access

Core

In Figure 3-5, a typical packet between access sites follows these steps:

Step 1 The packet is Layer 2-switched toward a distribution switch.

Step 2 The distribution switch performs multilayer switching toward a core interface.

Step 3 The packet is Layer 2-switched across the LAN core.

Step 4 The receiving distribution switch performs multilayer switching toward an access layer LAN.

Step 5 The packet is Layer 2-switched across the access layer LAN to the destination host.

Figure 3-6 shows an example of multilayer switching in the campus core.

Figure 3-6 Multilayer Switching in the Campus Core

Distribution Layer Routers Peer with Core Routers and Exchange Routing Information

Redundant Links and Core Devices Provide

High Level of Resilience

In Figure 3-6, a typical packet between access sites follows these steps:

Step 1 The packet is Layer 2-switched toward a distribution switch.

Step 2 The distribution switch performs multilayer switching toward a core interface.

Step 3 The packet is multilayer-switched across the LAN core.

Step 4 The receiving distribution switch performs multilayer switching toward an access LAN.

Step 5 The packet is Layer 2-switched across the access layer LAN to the destination host.

Figure 3-6 Multilayer Switching in the Campus Core

Core Layer

Distribution Layer Routers Peer with Core Routers and Exchange Routing Information

Redundant Links and Core Devices Provide

High Level of Resilience

Continue reading here: Using a Modular Approach to Network Design

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Readers' Questions

  • enzo
    Which tier in the threetiered network is responsible for routing traffic in and out of a network?
    1 month ago
    • The tier responsible for routing traffic in and out of a network is the middle tier, also known as the application or logic tier. This tier handles the communication between the user interface (front-end) and the database/storage (back-end). It is important to note that in a three-tiered network architecture, the first tier is the presentation tier responsible for the user interface, while the third tier is the data tier responsible for data storage and retrieval.
    • semrawit
      Which of the followwing function network layer doesn't support?
      5 months ago
      • ? Flow control
      • JENNIFER
        Which one of the following is layer3 device?
        5 months ago
        • A layer 3 device is a network device that can perform the same functions as a router, such as IP routing, packet forwarding, packet filtering, and data traffic management. Layer 3 devices include routers, switches, and firewalls.
        • Bercilac
          Which of the following technologies is not typically considered for an increase in redundancy?
          6 months ago
          • Fax machines
          • magnus
            Which of the following is not true about layer3 switches?
            7 months ago
            • Layer3 switches do not support dynamic routing protocols.
            • mike freud
              Which of the following is not a benefit of packet switched services?
              7 months ago
              • Lack of reliability
              • berhane michael
                Which of the following is a characteristic of a star topology?
                7 months ago
                • A star topology is characterized by a central device, such as a hub or switch, to which all other nodes are connected with dedicated point-to-point links.
                • Ursula Schmitz
                  What is one function of a layer 2 switch?
                  7 months ago
                  • One function of a layer 2 switch is to forward data frames between devices on the same LAN segment, based on the MAC addresses of the source and destination.
                  • Immacolata
                    Which of the following is not a benefit of layer 2 switching?
                    7 months ago
                    • A. Improved access control and security.
                    • gloriana
                      Which of the following is not true about switched backbones?
                      8 months ago
                      • Switched backbones do not typically use traditional routing protocols.
                      • rosamunda
                        Which technology is required when switched networks are designed to include redundant links?
                        8 months ago
                        • Spanning Tree Protocol (STP) is required when designing switched networks with redundant links. STP helps prevent loops in the network by selectively disabling links that are not necessary, while allowing redundant links to be used in the event of a failure.
                        • eglantine
                          What is a definition of a twotier lan network design?
                          8 months ago
                          • A two-tier LAN network design is a type of hierarchical network topology wherein multiple layers of switches are used to extend the local area network’s reach. In this design, the top tier consists of the backbone switches, which provide the primary connection between multiple lower-tier switches. This lower tier of switches then connects to the actual devices on the network, such as computers, routers, and printers.
                          • meeri lenkkeri
                            What is the use of devics in core layer?
                            9 months ago
                            • The core layer in a network is responsible for providing high-speed and reliable forwarding of packets. Devices in the core layer are typically routers that are optimized for speed and reliability. These routers can forward packets quickly and reliably between different networks. The core layer is also responsible for providing Quality of Service (QoS) to ensure priority delivery of packets in real-time applications such as VoIP, video, and multimedia streams.
                            • kiera
                              How is faliure implemented in the core layer?
                              1 year ago
                              • Failure is typically not implemented directly in the core layer. It is usually handled in the application layer. The core layer will usually receive errors from the application layer and process them accordingly. The core layer may also provide certain components that can detect, log, and report when errors occur.
                              • stephan
                                How a core layer connect to network?
                                1 year ago
                                • A core layer typically connects to a network by interconnecting routers or switches. The core layer is usually located between the distribution and access layers of the network. This layer establishes core paths between the switches and routers in the distribution layer and provides high-bandwidth switching and routing capabilities to support the access layer devices. The core layer also establishes various network services such as Quality of Service (QoS), Quality of Experience (QoE), and security.
                                • Marcus
                                  What should be the core layer of network design?
                                  1 year ago
                                  • The core layer of a network design should be the distribution layer. This is the layer that provides the connection between the access layer and the core layer of the network. It is responsible for the routing, switching, and security functions of the network.
                                  • MIMOSA
                                    Which of the following describe the core layer?
                                    1 year ago
                                    • The core layer is responsible for high-speed packet switching, providing the backbone of the network architecture.