Core layer switches 5.2.6 The core layer is the backbone of the campus switched network. The switches in this layer can make use of a number of Layer 2 technologies. Provided that the distance between the core layer switches is not too great, the switches can use Ethernet technology. Other Layer 2 technologies such as ATM cell switching, can also be used. In a network design, the core layer can be a routed, or Layer 3, core. Core layer switches are designed to provide efficient Layer 3 functionality when needed. Factors such as need, cost, and performance should be considered before a choice is made. The following Cisco switches are suitable for the core layer: Catalyst 6500 series Catalyst 8500 series IGX 8400 series Lightstream 1010 This page concludes this lesson. The next page will summarize the main points from this module.
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Distribution layer switches 5.2.4 This page will explain the features and functions of distribution layer switches. Distribution layer switches are the aggregation points for multiple access layer switches. The switch must be able to accommodate the total amount of traffic from the access layer devices. The distribution layer switch must have high performance. The distribution layer switch is a point at which a broadcast domain is delineated. The distribution layer combines VLAN traffic and is a focal point for policy decisions about traffic flow. For these reasons, distribution layer switches operate at both Layer 2 and Layer 3 of the OSI model. Switches in this layer are referred to as multilayer switches. These multilayer switches combine the functions of a router and a switch in one device. They are designed to switch traffic to gain higher performance than a standard router. If they do not have an associated router module, then an external router is use...
Access layer switches 5.2.2 Access layer switches operate at Layer 2 of the OSI model and provide services such as VLAN membership. The main purpose of an access layer switch is to allow end users into the network. An access layer switch should provide this functionality with low cost and high port density. The following Cisco switches are commonly used at the access layer: Catalyst 1900 series Catalyst 2820 series Catalyst 2950 series Catalyst 4000 series Catalyst 5000 series The Catalyst 1900 or 2820 series switch is an effective access device for small or medium campus networks. The Catalyst 2950 series switch effectively provides access for servers and users that require higher bandwidth. This is achieved with Fast Ethernet capable switch ports. The Catalyst 4000 and 5000 series switches include Gigabit Ethernet ports and are effective access devices for a larger number of users in large campus networks. The Interactive Med...
LAN Switches Switched LANs, access layer overview 5.2.1 The construction of a LAN that satisfies the needs of both medium and large-sized organizations is more likely to be successful if a hierarchical design model is used. The use of a hierarchical design model will make it easier to make changes to the network as the organization grows. This page will discuss the three layers of the hierarchical design model: The access layer provides users in workgroups access to the network. The distribution layer provides policy-based connectivity. The core layer provides optimal transport between sites. The core layer is often referred to as the backbone. This hierarchical model applies to any network design. It is important to realize that these three layers may exist in clear and distinct physical entities. However, this is not a requirement. These layers are defined to aid in successful network design and to represent functionality that must exist in ...
Layer 3 design 5.1.6 This page will describe some Layer 3 design considerations. A router is a Layer 3 device and is considered one of the most powerful devices in the network topology. Layer 3 devices can be used to create unique LAN segments. Layer 3 devices allow communication between segments based on Layer 3 addresses, such as IP addresses. Implementation of Layer 3 devices allows for segmentation of the LAN into unique physical and logical networks. Routers also allow for connectivity to WANs, such as the Internet. Layer 3 routing determines traffic flow between unique physical network segments based on Layer 3 addresses. A router forwards data packets based on destination addresses. A router does not forward LAN-based broadcasts such as ARP requests. Therefore, the router interface is considered the entry and exit point of a broadcast domain and stops broadcasts to other LAN segments. Routers provide scalability because they serve as fire...
Layer 2 design 5.1.5 This page will discuss some important Layer 2 design considerations. The purpose of Layer 2 devices in the network is to switch frames based on destination MAC address information, provide error detection, and to reduce congestion in the network. The two most common Layer 2 network devices are bridges and LAN switches. Devices at Layer 2 determine the size of the collision domains. Collisions and collision domain size are two factors that negatively affect the performance of a network. Microsegmentation of the network reduces the size of collision domains and reduces collisions. Micro segmentation is implemented through the use of bridges and switches. The goal is to boost performance for a workgroup or a backbone. Switches can be used with hubs to provide the appropriate level of performance for different users and servers. Another important characteristic of a LAN switch is how it allocates bandwidth on a per-port basis. This pr...
Layer 1 design 5.1.4 when going over the Layer 1 design. It cannot be emphasized enough that the term Ethernet refers to a whole host of technologies. For purposes of the case study, have the students consider 10BASE-T, 10BASE-FL, 100BASE-TX, 100BASE-FX, 1000BASE-T, 1000BASE-SX, and 1000BASE-LX. These are currently the most common Ethernet varieties. Each variety of Ethernet specifies the following: The data rate — the number in front of BASE, in Mbps The signaling method — all use BASEband as opposed to Broadband signaling The medium type — Category 5, 5e, 6, and 7 UTP, multi-mode and single-mode optical fiber The maximum length — which ranges from 100 m to several km The best practices for teaching this TI include having the students do group work on the design activity, use Web research to check facts, prices, and other issues, and document their work in their engineering journals. This page will teach students how to design the Layer 1 ...