two devices. Layer 2 switches are used in the access layer. Web Links Understanding Network Models – The Cisco Network Design Model http://www.2000trainers.com/article.
aspx?articleID=56&page=1
Content 5.2 LAN Switches 5.2.2 Access layer switches 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: 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 by providing 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. Interactive Media Activity PhotoZoom: Cisco Catalyst 1912 In this PhotoZoom, the student will view a Cisco Catalyst 1912. Web Links Cisco Catalyst 2950 Series Switches http://www.cisco.com/en/US/products/
hw/switches/ps628/index.html
Content 5.2 LAN Switches 5.2.3 Distribution layer overview The distribution layer of the network is between the access and core layers. It helps to define and separate the core. The purpose of this layer is to provide a boundary definition in which packet manipulation can take place. Networks are segmented into broadcast domains by this layer. Policies can be applied and access control lists can filter packets. The distribution layer isolates network problems to the workgroups in which they occur. The distribution layer also prevents these problems from affecting the core layer. Switches in this layer operate at Layer 2 and Layer 3. In a switched network, the distribution layer includes several functions such as the following: Web Links Understanding Network Models – The Cisco Network Design Model http://www.2000trainers.com/article.
aspx?articleID=56&page=1
Content 5.2 LAN Switches 5.2.4 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 used for the Layer 3 function. The following Cisco switches are suitable for the distribution layer: Interactive Media Activity PhotoZoom: Cisco Catalyst 2950 In this PhotoZoom, the student will view a Cisco Catalyst 2950. Web Links Cisco Catalyst 4500 Series Switches http://www.cisco.com/en/US/products/
hw/switches/ps4324/index.html
Content 5.2 LAN Switches 5.2.5 Core layer overview The core layer is a high-speed switching backbone. If they do not have an associated router module, an external router is used for the Layer 3 function. This layer of the network design should not perform any packet manipulation. Packet manipulation, such as access list filtering, would slow down the switching of packets. Providing a core infrastructure with redundant alternate paths gives stability to the network in the event of a single device failure. The core can be designed to use Layer 2 or Layer 3 switching. Asynchronous Transfer Mode (ATM) or Ethernet switches can be used. Interactive Media Activity Point and Click: Core Layer Students completing this activity will be able to identify the key function of the core layer in the three layer design model. Web Links Understanding Network Models – The Cisco Network Design Model http://www.2000trainers.com/ article.aspx?articleID=56&page=1
Content 5.2 LAN Switches 5.2.6 Core layer switches 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 Asynchronous Transfer Mode (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: Interactive Media Activity PhotoZoom: Cisco Catalyst 4006 In this PhotoZoom, the student will view a Cisco Catalyst 4006. Web Links Cisco Catalyst 6500 Series Switches http://www.cisco.com/en/US/products/
hw/switches/ps708/index.html
Content Summary An understanding of the following key points should have been achieved: