ccna certification validity

ccna certification validity.7.1.4 Switching Network HierarchyUsing a hierarchical network design in an enterprise campus network is easier to manage and scale the network, and troubleshooting is faster. A typical hierarchical design model can be divided into an access layer, a distribution layer, and a core layer. In small and medium-sized networks, a tight design is often used, where the distribution and core layers are combined into one, with each layer described below.1. Access LayerThe Access layer is responsible for connecting end devices (such as PCs, printers, wireless access points, and IP phones) to provide access to the rest of the network. The primary purpose of the access layer is to provide a way to connect devices to the network and to control which devices on the network are allowed to communicate with each other. Access layer devices are usually Layer 2 switches, such as Cisco's 29 series switches.2. Distribution Layer (Distribution)The distribution layer aggregates the data sent by the access layer switches, then transmits it to the core layer and finally to the final destination. The distribution layer uses policies to control the traffic on the network and delineates broadcast domains by performing routing functions between virtual LANs (VLANs) defined at the access layer. Using VLANs, traffic on a switch can be divided into different segments and placed on separate subnets from each other. Distribution layer devices are usually Layer 3 switches, such as Cisco's 35, 37, and 38 series switches.3. Core ( Core) layer.The core layer aggregates traffic sent by all distribution layer devices, and it is important to maintain high availability and redundancy because it must be able to forward large amounts of data quickly. Core layer devices are also typically Layer 3 switches, such as Cisco's 65 and other series switches.Layer 3 switches are typically deployed at the core and distribution layers of a switched network and feature the ability to build routing tables, support some routing protocols, and forward IP packets at rates close to those of Layer 2 forwarding. Layer 3 switches support dedicated hardware such as ApplicationSpecificIntegratedCircuit (ASIC). o ASICs used in conjunction with dedicated software data structures can simplify CPU-independent IP packet forwarding.7.1.5 Switch Selection