ccna wireless practice lab

ccna wireless practice lab.Cisco's hierarchical model of the enterprise campus consists of three layers: the core, distribution, and access layers, as shown in Figure 13.1. Well-designed campus networks typically use this topology. As the name implies, the core layer is the backbone of the network and provides high-speed connectivity between devices at the distribution layer. To provide high-speed connectivity, the core layer consists of high-speed switches that typically do not perform any type of packet and frame operations, such as filtering. The core layer uses Layer 2 switches or Layer 3 switches (usually the latter) and Gigabit connections, and sometimes EtherChannels (which are discussed at the end of this chapter). Traffic flowing through the core layer typically has to access enterprise resources: Internet connections, WAN connections, and applications on servers in a campus server farm.Practical Experience Layer 3 switches are actually routers that use an application-specific integrated circuit (ASIC) rather than a CPU to perform switching (the ASIC is discussed in Chapter 4, and it is discussed in more detail later in this chapter) When the I0S image used is appropriate, some Cisco switches support thisfeature, which includes Catalyst 3500 and higher switches.Layer 3 switches are most commonly used to connect the access layer to the distribution layer at the core, which typically uses Gigabit Ethernet but occasionally uses Fast Ethernet as well. In smaller networks, the distribution layer may also use Layer 2 switches. The responsibilities of the distribution layer include.. Prohibiting the propagation of broadcasts between layers through Layer 3 isolation (such as VLANs).. Filtering traffic between subnets using access control lists (ACLs are discussed in Chapter 22); . Providing hierarchy through Layer 3 logical addressing and route summarization; . Translating between different media types.Figure 13.1 Cisco's hierarchical model implements Layer 3 isolation between the core and access layers, but uses Layer 2 between the distribution layer switches and the access layer switches, so there are Layer 2 loops. In the three-layer hierarchical model, the lowest layer is the access layer. In effect, the access layer is located at the periphery of the campus network, and the distribution layer separates it from the core layer. The primary function of the access layer is to provide network connectivity to users, and this connectivity is typically provided by Layer 2 switches or wireless access points. Exam Essentials Cisco provides online design tools to help you select the right devices and uplinks for your three-tier network." in the basic design. the level of Oversubscription should not be too high. the ratio of the number of access layer links to the number of distribution layer links should not exceed 20:1. oversubscription refers to traffic from user access connections. is too much traffic from user access connections and the access layer switch does not have enough bandwidth to carry it to the distribution layer (oversubscription is discussed in more depth in Chapter 25). In addition, the ratio of the number of distribution layer links to the number of core layer links should not exceed 4: "However, the appropriate solution varies from case to case° Rate limiting is typically used to prohibit user oversubscription so as not to cause problems for other users or applications.13.1.2 Layer 2 ProblemsIn Figure 13.1, a redundant design is used: the access layer switch has two links to the distribution layer, and there are multiple Layer 2 connections between the distribution layer switches (usually EtherChannel) This redundancy typically results in a Layer 2 loop in the network, which in turn causes the following Layer 2 problemsLayer 2 problems: . . multiple frame copies; . Broadcast storms .