LAN Design

LAN Design

 

Overview

The previous chapter, "VLANs," provided an introduction to virtual LANs (VLANs) and switched internetworking, compared traditional shared local-area network (LAN) configurations with switched LAN configurations, and discussed the benefits of using a switched VLAN architecture. Despite improvements in equipment performance and media capabilities, network design is becoming more difficult. The trend is toward increasingly complex environments involving multiple media and interconnection to networks outside any single organization's controlled LAN. Keeping all the many factors in mind is important because carefully designing networks can reduce the hardships associated with growth as a networking environment evolves. One of the most critical steps to ensure a fast and stable network is the design of the network. If a network is not designed properly, many unforeseen problems can arise, and network growth can be jeopardized. This design process is truly an in-depth process. This chapter provides an overview of the LAN design process. In addition, LAN design goals, network design issues, network design methodology, and the development of LAN topologies are covered in this chapter.   Threaded Case Study     Washington Project: Designing the Network In this chapter, you will begin the process of designing the LAN at your specific site within Washington School District WAN. As concepts and requirements are introduced, you will be able to apply them in your network design. You will need to make sure to address the following requirements: The LAN is meant to serve different "workgroups" of staff members and students. This logical division will require the use of VLANs and will be a major design decision. For example, VLANs should be used to secure the administrators' machines from the students' machines. Access to the Internet from any site in the school district, via the District WAN, is also an integral part of this implementation. A series of servers is needed to facilitate online automations of all the district's administrative functions and many of the curricular functions. Because this network implementation must be functional for a minimum of 7-10 years, all design considerations should include at least 100x (times) growth in the LAN throughput, 2x (times) growth in WAN throughput, and 10x (times) growth in the Internet connection throughput. A minimum of 1.0 Mbps to any host computer in the network and 100 Mbps to any server host in the network is required. Only two routed protocols may be implemented in the network: TCP/IP and Novell IPX.

 

4.1 LAN Design Goals and Components

4.1.1 LAN design goals

Designing a network can be a challenging task, and involves more than just connecting computers together. A network requires many features in order to be scalable and manageable. To design reliable, scalable networks, network designers must realize that each of the major components of a network has distinct design requirements. Even a network that consists of only fifty nodes can pose complex problems that lead to unpredictable results. Attempting to design and build networks that contain thousands of nodes can pose even more complex problems. The first step in designing a LAN is to establish and document the goals of the design. These goals are particular to each organization or situation. However, the following requirements tend to show up in most network designs: Functionality-The network must work. That is, it must allow users to meet their job requirements. The network must provide user-to-user and user-to-application connectivity with reasonable speed and reliability. Scalability-The network must be able to grow. That is, the initial design should grow without any major changes to the overall design. Adaptability-The network must be designed with an eye toward future technologies, and it should include no element that would limit implementation of new technologies as they become available. Manageability-The network should be designed to facilitate network monitoring and management to ensure ongoing stability of operation. These requirements are specific to certain types of networks and more general in other types of networks. This chapter discusses how to address these requirements.

 

4.1.2 Critical components of LAN design

With the emergence of high-speed technologies such as Asynchronous Transfer Mode (ATM) and more complex LAN architectures that use LAN switching and VLANs over the past several years, many organizations have been upgrading existing LANs or planning, designing, and implementing new LANs. To design LANs for high-speed technologies and multimedia-based applications, network designers should address the following critical components of the overall LAN design: The function and placement of servers Collision detection Segmentation Bandwidth versus broadcast domains These components are discussed in the following sections.

 

4.1.3 The function and placement of servers when designing a network

One of the keys to designing a successful network is to understand the function and placement of servers needed for the network. Servers provide file sharing, printing, communication, and application services, such as word processing. Servers typically do not function as workstations; rather, they run specialized operating systems, such as NetWare, Windows NT, UNIX, and Linux. Today, each server usually is dedicated to one function, such as e-mail or file sharing. Servers can be categorized into two distinct classes: enterprise servers and workgroup servers. An enterprise server supports all the users on the network by offering services, such as e-mail or Domain Name System (DNS). E-mail or DNS is a service that everyone in an organization (such as the Washington School District) would need because it is a centralized function. On the other hand, a workgroup server supports a specific set of users, offering services such as word processing and file sharing, which are services only a few groups of people would need. Enterprise servers should be placed in the main distribution facility (MDF). This way, traffic to the enterprise servers has to travel only to the MDF and does not need to be transmitted across other networks. Ideally, workgroup servers should be placed in the intermediate distribution facilities (IDFs) closest to the users accessing the applications on these servers. You merely need to directly connect servers to the MDF or IDF. By placing workgroup servers close to the users, traffic only has to travel the network infrastructure to that IDF, and does not affect other users on that network segment. Within the MDF and IDFs, the Layer 2 LAN switches should have 100 Mbps or more allocated for these servers.   Threaded Case Study   Washington Project: Server Placement and Function You should categorize all file servers for the Washington School District as enterprise or workgroup types, and then place servers in the network topology according to the anticipated traffic patterns of users and according to the following functions: DNS and E-Mail Services - Each district hub location should contain a DNS server to support the individual schools serviced out of that location. Each school should also contain a host for DNS and e-mail services (that is, a local post office) that will maintain a complete directory of the staff members and students for that location. The Administrative Server - Each school location should have an administration server for the student tracking, attendance, grading, and other administrative functions. This server should run TCP/IP as its protocol suite and should be made available only to teachers and staff members. The Library Server - The school district is implementing an automated library information and retrieval system for an online curricular research library. This server should run TCP/IP as its OSI Layer 3 and Layer 4 protocol and should be made available to anyone at the school site. Application Server - All computer applications, such as word processing and spreadsheet software, should be housed in a central server at each school location. Other Servers - Any other servers implemented at the school sites should be considered departmental (workgroup) servers, and should be placed according to user group access needs. An example would be a server running an instructional application for a specific school site.

 

4.1.4 Intranet

One common configuration of a LAN is an intranet. Intranet Web servers differ from public Web servers in that, without the needed permissions and passwords, the public does not have access to an organization's intranet. Intranets are designed to be accessed by users who have access privileges to an organization's internal LAN. Within an intranet, Web servers are installed in the network, and browser technology is used as the common front-end to access information, such as financial data or graphical and text-based data stored on those servers. The addition of an intranet on a network is just one of many application and configuration features that can cause an increase in needed network bandwidth over current levels. Because bandwidth has to be added to the network backbone, network administrators should also consider acquiring robust desktops to get faster access into intranets. New desktops and servers should be outfitted with 10/100-Mbps Ethernet network interface cards (NICs) to provide the most configuration flexibility, thus enabling network administrators to dedicate bandwidth to individual end stations as needed.

 

4.1.5 Why contention is an issue with Ethernet

You should decide carefully on the selection and placement of networking devices to be used in the LAN in order to decrease the collision detection and media contention on a network. Contention refers to excessive collisions on Ethernet caused by too many devices, each with a great demand for the network segment. The number of broadcasts becomes excessive when there are too many client packets looking for services, too many server packets announcing services, too many routing table updates, and too many other broadcasts dependent on the protocols, such as Address Resolution Protocol (ARP). An Ethernet node gets access to the wire by contending with other Ethernet nodes for the right to do so. When your network grows to include more nodes on the shared segment or wire, and these nodes have more and more messages to transmit, the chance that a node will contend successfully for its share of the wire gets much worse, and the network bogs down. The fact that contention media access does not scale or allow for growth, is Ethernet's main disadvantage. As shown in the Figure, as traffic increases on the shared media, the rate of collisions also increases. Although collisions are normal events in Ethernet, an excessive number of collisions will (sometimes dramatically) reduce available bandwidth. In most cases, the actual available bandwidth is reduced to a fraction (about 35% to 40%) of the full 10 Mbps. This reduction in bandwidth can be remedied by segmenting the network by using bridges, switches, or routers.

 

4.1.6 How broadcast domains relate to segmentation

Segmentation is the process of splitting a single collision domain into two or more collision domains, as shown in Figure . Layer 2 (the data link layer) bridges or switches can be used to segment a logical bus topology and create separate collision domains, which results in more bandwidth being available to individual stations. Notice in Figure that the entire bus topology still represents a single broadcast domain because, although bridges and switches do not forward collisions, they forward broadcast packets. All broadcasts from any host in the same broadcast domain are visible to all other hosts in the same broadcast domain. Broadcasts must be visible to all hosts in the broadcast domain in order to establish connectivity. The scalability of the bandwidth domain depends on the total amount of traffic, and the scalability for a broadcast domain depends on the total broadcast of the traffic. It is important to remember that bridges and switches forward broadcast (FF-FF-FF-FF-FF) traffic, and that routers normally do not.

 

4.1.7 The difference between bandwidth and broadcast domains

A bandwidth domain is everything associated with one port on a bridge or switch . In the case of an Ethernet switch, a bandwidth domain is also known as a collision domain. All workstations within one bandwidth domain compete for the same LAN bandwidth resource. All the traffic from any host in the bandwidth domain is visible to all the other hosts. In the case of an Ethernet collision domain, two stations can transmit at the same time, causing a collision.

 

4.2 Network Design Methodology

4.2.1 Gathering and analyzing requirements

For a LAN to be effective and serve the needs of its users, it should be designed and implemented according to a planned series of systematic steps, which include the following: Gathering the users' requirements and expectations Analyzing requirements Designing the Layer 1, 2, and 3 LAN structure (that is, topology) Documenting the logical and physical network implementation The first step in designing a network should be to gather data about the organizational structure. This information includes the organization's history and current status, projected growth, operating policies and management procedures, office systems and procedures, and the viewpoints of the people who will be using the LAN. You need to answer the following questions: Who are the people who will be using the network? What is their level of skill, and what are their attitudes toward computers and computer applications? Answering these and similar questions will help determine how much training will be required and how many people will be needed to support the LAN. Ideally, the information gathering process helps clarify and identify the problems. You also need to determine whether there are documented policies in place. Has some data been declared mission critical? Have some operations been declared mission critical? (Mission-critical data and operations are those that are considered key to businesses, and access to them is critical to the business running on a daily basis.) What protocols are allowed on the network? Are only certain desktop hosts supported? Next, you should determine who in the organization has authority over addressing, naming, topology design, and configuration. Some companies have a central Management Information Systems (MIS) department that controls everything. Some companies have very small MIS departments and, therefore, must delegate authority to departments. Focus on identifying the resources and constraints of the organization. Organization resources that can affect the implementation of a new LAN system fall into two general categories: computer hardware/software and human resources. An organization's existing computer hardware and software must be documented, and projected hardware and software needs identified. How are these resources currently linked and shared? What financial resources does the organization have available? Documenting these types of things helps you estimate costs and develop a budget for the LAN. You should make sure you understand performance issues of any existing network.     Threaded Case Study     Washington Project: Understanding the Customer First and foremost, you must understand the customer. In the case of the Washington School District, you need to talk to major users of the network; find out their geographic location, their current applications; their plans for the future; and determine who the major players will be in helping you design the network. After you have gathered data on the district's organizational structure, you need to: Determine where information flows in the district Find out where shared data resides and who uses it Determine whether data outside the district-for example, data on the Internet-is accessed Define the issues or problems that need to be addressed

 

4.2.2 Factors that affect network availability

Availability measures the usefulness of the network. Many things affect availability, including the following: Throughput Response time Access to resources Every customer has a different definition of availability. For example, there may be a need to transport voice and video over the network. However, these services require more bandwidth than is available on the network or backbone. You can increase availability by adding more resources, but resources drive up cost. Network design seeks to provide the greatest availability for the least cost. After considering availability, the next step in designing a network is to analyze the requirements of the network and its users that were gathered in the last step. Network user needs constantly change. For example, as more voice- and video-based network applications become available, the pressure to increase network bandwidth will become intense. Another component of the analysis phase is assessing the user requirements. A LAN that is incapable of supplying prompt and accurate information to its users is of little use. Therefore, you must take steps to ensure that the information requirements of the organization and its workers are met.   Threaded Case Study    Washington Project: Availability Find out what availability means to your customer. In the case of the Washington School District, you need to conduct a detailed analysis of current and projected needs in order to help meet this need. Analysis of network requirements includes analyzing the district's business and technical goals. You need to answer the following questions: What applications will be implemented? What new networks will be accessed? What are the success criteria? What level of reliability must the WAN and LANs have? How can you tell if the new design is successful?     Threaded Case Study     Washington Project: Determining Network Traffic Load You need to determine the network traffic load for the Washington School District before developing a network structure and acquiring hardware. Additionally, when analyzing the district's technical requirements, you should estimate the traffic load caused by applications in packet size (for example, you need to estimate the size of files in bytes per second needed to be transmitted over the network). Certain types of network use can generate large volumes of traffic and, therefore, can cause congestion, including congestion of the following: Internet access Computers loading software from a remote site Anything that transmits images or video Central database access Department file servers You should estimate worst-case traffic load on the network during the busiest times for users and during regularly scheduled network services, such as file server backups.

 

4.2.3 Physical topologies used in networking

After determining the overall requirements for the network, the next step is to decide on an overall LAN topology that will satisfy the user requirements. In this curriculum, we concentrate on the star topology and extended star topology. As you have seen, the star/extended star topology uses Ethernet 802.3 carrier sense multiple access collision detect (CSMA/CD) technology. The reason that this curriculum focuses on a CSMA/CD star topology is that it is by far the dominant configuration in the industry. The major pieces of a LAN topology design can be broken into three unique categories of the OSI reference model-the network layer, the data link layer, and the physical layer. These components are discussed in the following sections.

 

 

 

4.3 Layer 1 Design

4.3.1 Designing the layer 1 topology: signaling method, medium type, and maximum length

In this section, you will examine Layer 1 star and extended star topologies. The physical cabling is one of the most important components to consider when designing a network. Design issues include the type of cabling to be used (typically copper or fiber) and the overall structure of the cabling. Layer 1 cabling media include types such as Category 5 unshielded twisted-pair (UTP) and fiber-optic cable, along with the TIA/EIA-568-A standard for layout and connection of wiring schemes. In addition to distance limitations, you should carefully evaluate the strengths and weaknesses of various topologies, as a network is only as effective as its underlying cable. Keep in mind that most network problems are caused by Layer 1 issues. If you are planning any significant changes for a network, you should do a complete cable audit to identify areas that require upgrades and rewiring. Whether you are designing a new network or recabling an existing one, fiber-optic cable should be used in the backbone and risers, with Category 5 UTP cable in the horizontal runs. The cable upgrade should take priority over any other needed changes, and enterprises should ensure-without exception-that these systems conform to well-defined industry standards, such as the TIA/EIA-568-A specifications. The TIA/EIA-568-A standard specifies that every device connected to the network should be linked to a central location with horizontal cabling. This is true if all the hosts that need to access the network are within the 100-meter distance limitation for Category 5 UTP Ethernet, as specified by TIA/EIA-568-A standards. The table in figure lists cable types and their characteristics. Upcoming Changes in Cabling Standards     Threaded Case Study    Washington Project: Speed and Expansion For the Washington School District network, you need to build the Layer 1 components of the district network with speed and expansion capabilities. As you know, the physical layer controls the way data is transmitted between the source and a destination node. Therefore, the type of media and topology you select helps you determine how much data can travel across the network and how quickly.

 

4.3.2 Diagramming a standards-based Ethernet cable run from the workstation to the HCC, including distances

In a simple star topology with only one wiring closet, the MDF includes one or more horizontal cross-connect (HCC) patch panels. HCC patch cables are used to connect the Layer 1 horizontal cabling with the Layer 2 LAN switch ports. The uplink port of the LAN switch, depending on the model, which is unlike other ports because it does not cross over, is connected to the Ethernet port of the Layer 3 router using patch cable. At this point, the end host has a complete physical connection to the router port.   Threaded Case Study    Washington Project: Catchment Areas You should review the TCS Overview to determine what the user expects for the number of horizontal cable runs to each room that the MDF or IDF will be servicing in its catchment area.

 

4.3.3 HCC, VCC, MDF, IDF, and POP

When hosts in larger networks are outside the 100-meter limitation for Category 5 UTP, it is not unusual to have more than one wiring closet. By creating multiple wiring closets, multiple catchment areas are created. The secondary wiring closets are referred to as IDFs. TIA/EIA 568-A Standards specify that IDFs should be connected to the MDF by using vertical cabling, also called backbone cabling. As shown in figure , A vertical cross-connect (VCC) is used to interconnect the various IDFs to the central MDF. Because the vertical cable lengths typically are longer than the 100-meter limit for Category 5 UTP cable, fiber-optic cabling normally is used, as shown in figure .   Threaded Case Study     Washington Project: Connection Speeds In the Washington School District network, the vertical cabling should carry all data traffic between the IDFs and MDFs. Therefore, the speed of this connection should be designed to be the fast link in the network. All traffic across the district network backbone will traverse this link, so this link should be at least 100 Mbps.

 

4.3.4 10BASE-T and 100BASE-TX ethernet

Fast Ethernet is Ethernet that has been upgraded to 100 Mbps. This type uses the standard Ethernet broadcast-oriented logical bus topology of 10BASE-T, along with the familiar CSMA/CD method for Media Access Control (MAC). The Fast Ethernet standard is actually several different standards based on copper-pair wire (100BASE-TX) and on fiber-optic cable (100BASE-FX), and it is used to connect the MDF to the IDF.   Threaded Case Study   Washington Project: LAN Wiring Scheme Requirements As you're planning the wiring for the sites of the Washington School District network, you need to take into account certain LAN requirements related to user access, segmentation, infrastructure, cabling, MDFs, and IDFs. Therefore, you should address the requirements described here when designing the network. Requirement 1 Two LAN segments need to be implemented in each school and the district office. One LAN needs to be designated for student/curriculum usage and the other needs to be designated for administration usage. Requirement 2 The LAN infrastructure needs to be based on Ethernet LAN switching, which will allow for a migration to faster speeds (that is, more bandwidth) to the individual computers and between MDFs and IDFs without revamping the physical wiring scheme to accommodate future applications. The transport speeds need to be Ethernet 10BASE-T, 100BASE-TX, and 100BASE-FX. Requirement 3 Horizontal cabling needs to be Category 5 UTP and needs to have the capacity to accommodate 100 Mbps. Vertical (backbone) cabling needs to be Category 5 UTP or fiber-optic multi-mode cable. The cabling infrastructure needs to comply with TIA/EIA-568-A and TIA/EIA-569 standards. Requirement 4 In each location, an MDF room needs to be established as the central point to which all LAN cabling will be terminated. This will also be the point of presence (POP) for the WAN connection. The IDF should service its geographical area, and the IDF should be connected directly to the MDF in a star or extended star topology.

 

4.3.5 Elements of a logical topology diagram

As shown in Figure , the logical diagram is the network topology model without all the detail of the exact installation path of the cabling. It is the basic road map of the LAN. Elements of the logical diagram include: The exact locations of the MDF and IDF wiring closets. The type and quantity of cabling used to interconnect the IDFs with the MDF, along with how many spare cables are available for increasing the bandwidth between the wiring closets. For example, if the vertical cabling between IDF 1 and the MDF is running at 80% utilization, you can use two additional pairs to double the capacity Detailed documentation of all cable runs, as shown in Figure , the identification numbers, and which port on the HCC or VCC the run is terminated on. For example, say Room 203 has lost connectivity to the network. By examining the cutsheet, you can see that Room 203 is running off cable run 203-1, which is terminated on HCC 1 port 13. You can now test that run by using a cable tester to determine whether the problem is a Layer 1 failure. If it is, you can simply use one of the other two runs to get the connectivity back and then troubleshoot run 203-1.   Threaded Case Study    Washington Project: Layer 2 Design Goals The following are Layer 2 LAN topology design goals for the sites of the Washington School District network: You should install LAN switching devices that use micro-segmentation in order to reduce the collision domain size. You should create VLANs and unique broadcast domains based on user workgroups.

 

 

 

 

4.4 Explain Layer 2 Design

4.4.1 Common Layer 2 devices and their impact on network domains

As you learned previously in the "LAN Switching" chapter and in the "VLANs" chapter, the purpose of Layer 2 devices in the network is to provide flow control, error detection, error correction, and to reduce congestion in the network. The two most common Layer 2 devices (other than the NIC, which every host on the network must have) are bridges and LAN switches. Devices at this layer determine the size of the collision domains and broadcast domains. This section concentrates on the implementation of LAN switching at Layer 2.   Threaded Case Study     Washington Project: Layer 2 Design goals The following are Layer 2 LAN topology design goals for the sites of the Washington School District network: You should install LAN switching devices that use microsegmentation in order to reduce the collision domain size. You should create VLANs and unique broadcast domains based on user workgroups.

 

4.4.2 Asymmetric switching

Collisions and collision domain size are two factors that negatively affect the performance of a network. By using LAN switching, you can microsegment the network, thus eliminating collisions and reducing the size of collision domains. Another important characteristic of a LAN switch is how it can allocate bandwidth on a per-port basis, thus allowing more bandwidth to vertical cabling, uplinks, and servers. This type of switching is referred to as asymmetric switching, and it provides switched connections between ports of unlike bandwidth, such as a combination of 10-Mbps and 100-Mbps ports.

 

4.4.3 The effect microsegmentation can have on a network

As you have learned, microsegmentation means using bridges and switches to boost performance for a workgroup or a backbone. Typically, boosting performance in this manner involves Ethernet switching. Switches can be used with hubs to provide the appropriate level of performance for different users and servers.

 

4.4.4 Determining the number of cable runs and drops

By installing LAN a switch at the MDF and IDFs and vertical cable between the MDF and the IDFs, the vertical cable is carrying all the data traffic between the MDF and the IDFs. The capacity of this run must be larger than that of the runs between the IDFs and workstations. Horizontal cable runs use Category 5 UTP, and no cable drop should be longer than 100 meters, which allows links at 10 Mbps or 100 Mbps. In a normal environment, 10 Mbps is adequate for the horizontal cable drop. Because asymmetric LAN switches allow for mixing 10-Mbps and 100-Mbps ports on a single switch, the next task is to determine the number of 10-Mbps and 100- Mbps ports needed in the MDF and every IDF. This can be determined by going back to the user requirements for the number of horizontal cable drops per room and the number of drops total in any catchment area, along with the number of vertical cable runs. For example, say user requirements dictate that 4 horizontal cable runs be installed to each room. The IDF that services a catchment area covers 18 rooms. Therefore, 4 drops x 18 rooms = 72 LAN switch ports.   Threaded Case Study     Washington Project: LAN Topology Requirements As you're planning the LAN topology for your school site, you need to keep in mind certain requirements for rooms that need access to the network and the room's wiring POP. Requirement 1 Each room requiring connection to the network needs to be able to support 24 workstations and be supplied with four Category 5 UTP runs for data, with one run terminated at the teacher's workstation. These cable runs should be terminated in the closest MDF or IDF. All Category 5 UTP cable runs need to be tested end-to-end for 100 Mbps bandwidth capacity. Requirement 2 A single location in each room needs to be designated as the wiring POP for that room. It needs to consist of a lockable cabinet containing all cable terminations and electronic components that is, data hubs or switches). From this location, data services need to be distributed within the room via decorative wire molding. Network 1 needs to be allocated for general curriculum use, and Network 2 needs to be allocated for administrative use.

 

4.4.5 Determining the size of collision domains in hubbed and switched networks

To determine the size of a collision domain, you must determine how many hosts are physically connected to any single port on the switch. This also affects how much network bandwidth is available to any host. In an ideal situation, there is only one host connected on a LAN switch port. This would make the size of the collision domain 2 (the source host and destination host). Because of this small collision domain, there should be almost no collisions when any two hosts are communicating with each other. Another way to implement LAN switching is to install shared LAN hubs on the switch ports and connect multiple hosts to a single switch port. All hosts connected to the shared LAN hub share the same collision domain and bandwidth. Note that some older switches, such as the Catalyst 1700, don't truly support sharing the same collision domain and bandwidth because they don't maintain multiple MAC addresses mapped to each port. In that case, there are many broadcasts and ARP requests.

 

4.4.6 Diagramming hub placement in a standards-based extended star topology

Shared-media hubs are generally used in a LAN switch environment to create more connection points at the end of the horizontal cable runs. This is an acceptable solution, but you must ensure that collision domains are kept small and bandwidth requirements to the host are accomplished according to specifications gathered in the requirements phase of the network design process.

 

4.4.7 Migrating a network from 10 Mbps to 100 Mbps

As the network grows, the need for more bandwidth increases. In the vertical cabling between MDF and IDFs, unused fiber optics can be connected from the VCC to 100 Mbps ports on the switch. The network shown doubles the capacity of the vertical cabling in the network in the following graphic by bringing up another link. In the horizontal cabling, you can increase the bandwidth by a factor of 10 by repatching from the HCC to a 100 Mbps port on the switch and changing from a 10 Mbps hub to a 100 Mbps hub. When sizing the Layer 2 LAN switch, it is important to make sure there are enough 100 Mbps ports to allow for this migration to higher bandwidth. It is important to document the speed at which each active cable drop is running.

 

4.5 Layer 3 Design

4.5.1 Using routers as the basis for layer 3 network design

As shown in the Figure, Layer 3 (the network layer) devices, such as routers, can be used to create unique LAN segments and allow communication between segments based on Layer 3 addressing, such as IP addressing. Implementation of Layer 3 devices, such as routers, allows for segmentation of the LAN into unique physical and logical networks. Routers also allow for connectivity to wide-area networks (WANs), such as the Internet. Layer 3 routing determines traffic flow between unique physical network segments based on Layer 3 addressing, such as IP network and subnet. The router is one of the most powerful devices in the network topology. As you have learned, 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 from reaching other LAN segments.   Threaded Case Study     Washington Project: Layer 3 Design Goals The following are Layer 3 LAN topology design goals for the your site: Build a path between LAN segments that will filter the flow of data packets. Isolate ARP broadcasts. Isolate collisions between segments. Filter Layer 4 services between segments.

 

4.5.2 How VLANs can create smaller broadcast domains

One important issue in a network is the total number of broadcasts, such as ARP requests. By using VLANs, you can limit broadcast traffic to within a VLAN and thus create smaller broadcast domains. VLANs can also be used to provide security by creating the VLAN groups according to function. As shown in Figure , a physical port association is used to implement VLAN assignment. Ports P0, P1, and P4 have been assigned to VLAN 1. VLAN 2 has ports P2, P3, and P5. Communication between VLAN 1 and VLAN 2 can occur only through the router. This limits the size of the broadcast domains and uses the router to determine whether VLAN 1 can talk to VLAN 2. This means you can create a security scheme based on VLAN assignment.

 

4.5.3 Explain how a router provides structure to a network

Routers provide scalability because they can serve as firewalls for broadcasts. In addition, because Layer 3 addresses typically have structure, routers can provide greater scalability by dividing networks and subnets, therefore, adding structure to Layer 3 addresses. The ways in which greater scalability in networks can occur are shown in the table. When the networks are divided into subnets, the final step is to develop and document the IP addressing scheme to be used in the network. Routing technology filters data-link broadcasts and multicasts. By adding router ports with additional subnet or network addresses, you can segment the internetwork as required. Network protocol addressing and routing provide built-in scaling. When deciding whether to use routers or switches, remember to ask, "What problem am I trying to solve?" If your problem is protocol related rather than contention oriented, then routers are appropriate. Routers solve problems with excessive broadcasts, protocols that do not scale well, security issues, and network-layer addressing. Routers, however, are more expensive and harder to configure than switches.

 

4.5.4 Why large, scalable LANs need to incorporate routers

Routers can be used to provide IP subnets to add structure to addresses. With bridges and switches, all unknown addresses must be flooded out of every port. With routers, hosts using protocols with network-layer addressing can solve the problem of finding other hosts without flooding. If the destination address is local, the sending host can encapsulate the packet in a data-link header and send a unicast frame directly to the station. The router does not see the frame and, of course, does not need to flood the frame. The sending host might have to use ARP. This would cause a broadcast, but the broadcast is only a local broadcast and is not forwarded by the router. If the destination is not local, then the sending station transmits the packet to the router. The router sends the frame to the destination or to the next hop, based on its routing table. Given this routing functionality, it is clear that large, scalable LANs need to incorporate some routers.   Threaded Case Study    Washington Project: Addressing The district office should develop a complete TCP/IP addressing and naming convention scheme for all hosts, servers, and network interconnection devices. The implementation of unauthorized addresses should be prohibited. All computers located on the administrative networks should have static addresses. Curriculum computers should obtain addresses by utilizing Dynamic Host Configuration Protocol (DHCP). DHCP provides a mechanism for allocating IP addresses dynamically so that addresses can be reused when hosts no longer need them. While the district office should design, implement, and enforce the overall addressing scheme for the network, DHCP should be administered by the local sites within the confines of the address blocks they were assigned.

 

 

4.5.5 Diagramming a standards-based LAN that uses routers

The Figure shows an example of an implementation that has multiple physical networks. All data traffic from Network 1 destined for Network 2 has to go through the router. In this implementation, there are two broadcast domains. The two networks have unique Layer 3 IP addressing network/subnetwork addressing schemes. In a structured Layer 1 wiring scheme, multiple physical networks are easy to create simply by patching the horizontal cabling and vertical cabling into the appropriate Layer 2 switch using patch cables. As we will see in future chapters, this implementation provides for robust security implementation. In addition, the router is the central point in the LAN for traffic destination.

 

4.5.6 Logical and physical network maps

After you have developed the IP addressing scheme for the customer, you should document it by site and by network within the site. A standard convention should be set for addressing important hosts on the network. This addressing scheme should be kept consistent throughout the entire network. By creating addressing maps, you can get a snapshot of the network. Creating physical maps of the network helps you troubleshoot the network.   Lab Activity   The following lab will help prepare for the Case Study. In this lab you will be given some basic requirements for a small LAN that spans multiple buildings. Your focus is on the physical topology and Data link layer components. The goal is to replace an aging 10BASE2 thinnet Ethernet network with current technology Ethernet switches and cabling based on structured cabling standards and the extended star topology.

 

Summary

Now that you completed this chapter, you should have a firm understanding of the following: One of the most critical factors in ensuring a fast and stable network is the design of the network. If a network is not designed properly, many unforeseen problems may arise, and network growth can be jeopardized. LAN design goals include functionality, scalability, adaptability, and manageability. Network design issues include function and placement of servers, collision detection, segmentation, and bandwidth versus broadcast domains. The design process includes the following: Gathering the users requirements and expectations Determining data traffic patterns now and in the future based on growth and server placements Defining all the Layer 1, 2, and 3 devices, along with the LAN and WAN topology Documenting the physical and logical network implementation       Threaded Case Study       Washington School District Project Task: LAN Design In this chapter, you have learned concepts that will help you begin the design process for the Washington School District network. As part of the LAN design process, you need to complete the following tasks: Gather all information required to design a LAN for your group's assigned site in the Washington School District, starting with the TCS Overview but doing additional research as needed. Design the LAN for your school based on the requirements gathered in step 1, in the context of developing an overall IP addressing scheme for the school district. First, each group will separately develop an IP addressing scheme for the entire school district. This can be done a variety of ways, and diversity is encouraged so the class thinks through the pros and cons of DIFFERENT IP Addressing Schemes. Some ideas to consider are Class A, B, and C networks with proper subnetting; Network Address Translation (NAT), and Private Network numbers. Each group will present their IP addressing scheme and the class will agree on the one best implementation. The class will elect this one group as the Network Operations Center (NOC) contact who will control the distribution of all IP addresses. Once the NOC distributes IP address blocks to school sites, the individual school site groups can assign static and dynamic IP addresses within their individual LANs. Develop and document an overall LAN design based on the user and district requirements. To properly design your site's LAN, complete these tasks: A user requirements document (your interpretation and proposal of what is meant by the TCS Overview , the District and site needs, and your instructor's assignments) An overall design document, which includes a logical LAN design (logical topology) of the school and a complete physical design (physical topology) that includes: Details of all MDFs/IDFs in the rooms, including a to-scale diagram The number of HCCs, VCCs, and LAN switch ports required to meet the existing and projected growth needs LAN Electronics List: what devices (hubs, switches, routers, servers, others) are needed Specifications on the type and quantity of cable media for all horizontal and vertical runs Specifications on security, VLANs, and the separation of staff and student networks The overall district IP addressing scheme and how it is applied at the local school site An analysis of the pros and cons of the proposed LAN design 4. Apply the CCNA Certification Exam Learning Objectives to your specific design. This will require a paragraph on how the learning objectives relate to your design. Learning objectives can be grouped together for the purpose of explanation. In this way, you will be studying for their CCNA Certification Exam as you work through the case study. CCNA Certification Exam Learning Objectives (*** are explicit CCNA Exam objectives; unmarked are knowledge assumed by the exam): OSI model Identify and describe the functions of each of the seven layers of the OSI reference model.*** Describe the different classes of IP addresses [and subnetting].*** Define and explain the 5 conversion steps of data encapsulation.*** Addressing Define and describe the function of a MAC address. Describe data link addresses and network addresses, and identify the key differences between them.*** Identify the functions of the TCP/IP transport-layer protocols.*** Identify the functions of the TCP/IP network-layer protocols.*** Describe the different classes of IP addresses [and subnetting].*** Ethernet Describe network congestion problem in Ethernet networks.*** Describe full- and half-duplex Ethernet operation.*** Describe the features and benefits of Fast Ethernet.*** Describe the guidelines and distance limitations of Fast Ethernet.*** Segmentation Describe LAN segmentation using bridges.*** Describe LAN segmentation using routers.*** Describe LAN segmentation using switches.*** Describe the benefits of network segmentation with bridges.*** Describe the benefits of network segmentation with routers.*** Describe the benefits of network segmentation with switches.*** LAN Switching Name and describe two switching methods.*** Distinguish between cut-through and store-and-forward LAN switching.*** Describe the benefits of virtual LANs.*** Flow Control Define flow control and describe the three basic methods used in networking.***

VLANs

VLANs

 

Overview

The "LAN Switching" chapter discussed problems inherent(yang berhubungan) in a LAN and possible solutions to improve(memajukan) LAN performance(daya guna). You learned about the advantages and disadvantages of using bridges, switches, and routers for LAN segmentation and the effects of switching, bridging, and routing on network throughput. Finally, you briefly(singkat) learned about the benefits of Fast Ethernet and virtual local-area networks (VLANs). This chapter provides an introduction to VLANs and switched internetworking, compares traditional shared LAN configurations with switched LAN configurations, and discusses the benefits of using a switched VLAN architecture. Threaded Case Study Washington Project: VLANs As you begin the chapter on VLANs, think about why VLANs are being introduced. Also think about how, where, and when you might want to use VLANs at an elementary school site.

 

3.1 VLANS

3.1.1 Existing shared LAN configurations

A VLAN is a logical grouping of devices or users that can be grouped by function, department, or application, regardless(tanpa memperhatikan) of their physical segment location. VLAN configuration is done at the switch via software. VLANs are not standardized and require(membutuhkan) the use of proprietary(pemilik) software from the switch vendor. A typical LAN is configured according to the physical infrastructure(prasarana) it is connecting. Users are grouped based on their location in relation to the hub they are plugged in to and how the cable is run to the wiring closet. The router interconnecting each shared(bersama sama) hub typically(khususnya) provides segmentation and can act as a broadcast firewall. The segments created by switches do not. Traditional LAN segmentation does not group users according to their workgroup association or need for bandwidth. Therefore, they share the same segment and contend(berjuang) for the same bandwidth, although(walaupun) the bandwidth requirements(perlu) may vary(berubah ubah) greatly by workgroup or department.

 

3.2 Segmentation with Switching Architectures

3.2.1 Grouping geographically separate users into network-wide virtual topologies

LANs are increasingly(meluas) being divided(dibagi) into workgroups connected via common backbones to form VLAN topologies. VLANs logically segment(membagi) the physical LAN infrastructure(rangka dasar) into different subnets (or broadcast domains for Ethernet). Broadcast frames(susunan) are switched only between ports within the same VLAN. Initial VLAN implementations(pelaksanaan) offered(diberikan) a port-mapping(pemetaan) capability(mampu) that established(membuat) a broadcast domain between a default group of devices. Current(sekarang) network requirements demand(menuntut) VLAN functionality that covers(mencakup) the entire network. This approach(tiba) to VLANs allows you to group geographically separate users in networkwide virtual topologies. VLAN configurations group users by logical association(gabungan) rather than(lebih lagi) physical location. The majority(sebagian besar) of the networks currently(sekarang) installed provide(memberikan) very limited logical segmentation. Users are commonly grouped based on connections to the shared hub and the router ports between the hubs. This topology provides segmentation only between the hubs, which are typically located on separate floors, and not between users connected to the same hub. This imposes(penentuan) physical constraints(membatasi) on the network and limits how users can be grouped. A few shared-hub architectures have some grouping capability, but they restrict(membatasi) how you configure logically defined(ditetapkan) workgroups.

 

3.2.2 Differences between traditional switched LAN and VLANs

In a LAN that utilizes(menggunakan) LAN switching devices, VLAN technology is a cost-effective and efficient way of grouping network users into virtual workgroups regardless(tanpa memperhatikan) of their physical location on the network. The graphic shows the difference between LAN and VLAN segmentation. Some of the main differences are as follows: VLANs work at Layer 2 and Layer 3 of the OSI reference model. Communication between VLANs is provided by Layer 3 routing. VLANs provide a method of controlling network broadcasts. The network administrator assigns(menentukan) users to a VLAN. VLANs can increase network security by defining which network nodes can communicate with each other. Using VLAN technology, you can group switch ports and their connected users into logically defined workgroups, such as the following: Coworkers in the same department A cross-functional product team Diverse(bermacam) user groups sharing the same network application or software You can group these ports and users into workgroups on a single switch or on connected switches. By grouping ports and users together across multiple switches, VLANs can span(menjangkau) single-building infrastructures, interconnected buildings, or even wide-area networks (WANs).

 

3.2.3 The transport of VLANs across backbones

Important to any VLAN architecture is the ability to transport VLAN information between interconnected switches and routers that reside(terletak) on the corporate(hubungan) backbone. These transport capabilities: remove the physical boundaries(batas) between users increase the configuration flexibility of a VLAN solution when users move provide(menyediakan) mechanisms for interoperability between backbone system components. The backbone commonly acts as the collection point for large volumes of traffic(lalu lintas). It also carries end-user VLAN information and identification between switches, routers, and directly attached(diberikan) servers. Within the backbone, high-bandwidth, high-capacity links are typically chosen to carry the traffic throughout the enterprise(perusahaan).

 

3.2.4 The role(peranan) of routers in VLANs

The traditional role of a router is to provide firewalls, broadcast management and route processing and distribution. While VLAN switches take on some of these tasks, routers still remain(tetap) vital in VLAN architectures because they provide connected routes between different VLANs. They also connect to other parts of the network that are either(tiap) logically segmented with the more traditional subnet approach(menjelang) or require(membutuhkan) access to remote sites across wide-area links. Layer 3 communication, either embedded(disimpan) in the switch or provided externally, is an integral(utuh) part of any high-performance(daya guna) switching architecture. You can cost-effectively integrate(menggabungkan) external routers into the switching architecture by using one or more high-speed backbone connections. These are typically(khusus) Fast Ethernet, or ATM connections, and they provide benefits by: Increasing the throughput between switches and routers Consolidating(menggabungkan) the overall(keseluruhan) number of physical router ports required for communication between VLANs VLAN architecture not only provides logical segmentation, but, with careful(teliti) planning, it can greatly enhance(menambah) the efficiency of a network.

 

3.2.5 How frames are used in VLANs

Switches are one of the core(inti) components of VLAN communications. Each switch has the intelligence(kecerdasan) to make filtering(penyaring) and forwarding decisions by frame, based on VLAN metrics defined by network managers. The switch can also communicate this information to other switches and routers within the network. The most common approaches(menemui) for logically grouping users into distinct(berbeda) VLANs are frame filtering and frame identification (frame tagging(label)). Both of these techniques look at the frame when it is either received or forwarded by the switch. Based on the set of rules defined by the administrator, these techniques determine where the frame is to be sent, filtered, or broadcast. These control mechanisms can be centrally administered (with network management software) and are easily implemented throughout(diseluruh) the network. In their early days, VLANs were filter-based and they grouped users based on a filtering table. This model did not scale well because each frame had to be referenced to a filtering table. Frame tagging(label) uniquely(khusus) assigns(memberikan) a VLAN ID to each frame. The VLAN IDs are assigned to each VLAN in the switch configuration by the switch administrator. This technique was chosen by the Institute of Electrical and Electronic Engineers (IEEE) standards group because of its scalability. Frame tagging is gaining(mendapat) recognition(pengenalan) as the standard trunking(batang tubuh) mechanism; in comparison(perbandingan) to frame filtering, it can provide a more scalable solution to VLAN deployment that can be implemented campus-wide. IEEE 802.1q states that frame tagging is the way to implement VLANs. VLAN frame tagging is an approach(jalan) that has been specifically developed for switched communications. Frame tagging places a unique identifier in the header of each frame as it is forwarded throughout (disepanjang)the network backbone. The identifier(pengenalan) is understood(dimengerti) and examined(diperiksa) by each switch prior(utama) to any broadcasts or transmissions(pengiriman) to other switches, routers, or end-station devices. When the frame exits the network backbone, the switch removes the identifier before the frame is transmitted to the target end station. Frame identification functions at Layer 2 and requires little processing or administrative overhead(tambahan).

 

3.3 VLAN Implementation

3.3.1 The relationship between ports, VLANs, and broadcasts

A VLAN makes up a switched network that is logically segmented by functions, project teams, or applications, without regard(memperhatikan) to the physical location of users. Each switch port can be assigned(ditempatkan) to a VLAN. Ports assigned to the same VLAN share broadcasts. Ports that do not belong to that VLAN do not share these broadcasts. This improves(penambahan) the overall(keseluruhan) performance(daya guna) of the network. The following sections discuss three VLAN implementation methods that can be used to assign a switch port to a VLAN. They are: port-centric static dynamic

 

3.3.2 Why port-centric VLANs make an administrator's job easier

In port-centric VLANs, all the nodes connected to ports in the same VLAN are assigned to the same VLAN ID. The graphic shows VLAN membership by port, which make an administrator's job easier and the network more efficient because: Users are assigned by port. VLANs are easily administered. It provides increased security between VLANs. Packets do not "leak"(bocor) into other domains.

 

3.3.3 Static VLANs

Static VLANs are ports on a switch that you statically assign(ditempatkan) to a VLAN. These ports maintain(memelihara) their assigned VLAN configurations until you change them. Although static VLANs require the administrator to make changes, they are secure(aman), easy to configure, and straightforward(terus terang) to monitor. Static VLANs work well in networks in which moves are controlled and managed(diatur).

 

3.3.4 Dynamic VLANs

Dynamic VLANs are ports on a switch that can automatically determine their VLAN assignments(tugas). Dynamic VLAN functions are based on MAC addresses, logical addressing, or protocol type of the data packets. When a station is initially(pertama) connected to an unassigned(tidak ditentukan) switch port, the appropriate(tepat) switch checks the MAC address entry(masuk) in the VLAN management database and dynamically configures the port with the corresponding(cocok) VLAN configuration. The major benefits(keuntungan) of this approach(jalan) are less administration within the wiring closet when a user is added or moved and centralized(dipusat) notification(pemberitahuan) when an unrecognized user is added to the network. Typically(khusus), more administration is required up front to set up the database within the VLAN management software and to maintain an accurate(teliti) database of all network users. Lab Activity   In this lab you will work with Ethernet Virtual Local Area Networks or VLANs. VLANs can be used to separate groups of users based on function rather than physical location.     Lab Activity In this lab you will work with Virtual Local Area Networks (VLANs). You will console into the switch and view the menu options available to manage VLANs and will check the current(sekarang) VLAN configuration.

 

3.4 Benefits of VLANs

3.4.1 How VLANs make additions, moves, and changes easier

Companies are continuously(terus menerus) reorganizing(mereorganisasi). On average, 20% to 40% of the workforce physically moves every year. These moves, additions, and changes are one of a network manager's biggest headaches(persoalan) and one of the largest expenses(biaya) related(dihubungkan) to managing(mengurus) the network. Many moves require recabling, and almost all moves require new station addressing and hub and router reconfigurations. VLANs provide an effective mechanism for controlling these changes and reducing(pengurangan) much of the cost associated with hub and router reconfigurations. Users in a VLAN can share the same network address space(tempat) (that is, the IP subnet), regardless(tanpa memperhatikan) of their location. When users in a VLAN are moved from one location to another, as long as they remain(tetap) within the same VLAN and are connected to a switch port, their network addresses do not change. A location change can be as simple as plugging a user into a port on a VLAN-capable(mampu) switch and configuring the port on the switch to that VLAN. VLANs are a significant(penting) improvement (kemajuan) over(diatas) the typical(khusus) LAN-based techniques used in wiring closets because they require less rewiring, configuration, and debugging. Router configuration is left intact(utuh); a simple move for a user from one location to another does not create any configuration modifications in the router if the user stays in the same VLAN.

 

3.4.2 How VLANs help control broadcast activity

Broadcast traffic occurs in every network. Broadcast frequency(sering) depends on the types of applications, the types of servers, the amount(banyaknya) of logical segmentation, and how these network resources are used. Although applications have been fine-tuned(distem) over the past few years to reduce the number of broadcasts they send out, new multimedia applications are being developed that are broadcast and multicast intensive. You need to take preventive(pencegahan) measures(tindakan) to ensure against broadcast-related problems. One of the most effective measures is to properly(sebaiknya) segment the network with protective firewalls that, as much as possible, prevent(mencegah) problems on one segment from damaging other parts of the network. Thus(jadi), although one segment may have excessive(terlalu banyak) broadcast conditions, the rest(sisa) of the network is protected with a firewall commonly provided by a router. Firewall segmentation provides reliability(tahan uji) and minimizes the overhead of broadcast traffic, allowing for greater throughput of application traffic. When no routers are placed between the switches, broadcasts (Layer 2 transmissions) are sent to every switched port. This is commonly referred to as a flat(rata) network, where there is one broadcast domain across the entire network. The advantage of a flat network is that it can provide both low-latency and high-throughput performance and it is easy to administer. The disadvantage is that it increases(memperluas) vulnerability(mudah kena serang) to broadcast traffic across all switches, ports, backbone links, and users. VLANs are an effective mechanism for extending firewalls from the routers to the switch fabric (struktur)and protecting the network against potentially(sanggup) dangerous broadcast problems. Additionally, VLANs maintain all the performance benefits of switching. You create firewalls by assigning(menentukan) switch ports or users to specific VLAN groups both within single switches and across multiple connected switches. Broadcast traffic within one VLAN is not transmitted outside the VLAN. Conversely(sebaliknya), adjacent(berbatasan) ports do not receive(menerima) any of the broadcast traffic generated(dihasilkan) from other VLANs. This type of configuration substantially (banyaj) reduces(mengurangi) the overall(keseluruhan) broadcast traffic, frees bandwidth for real(nyata) user traffic, and lowers the overall vulnerability(kena serangan) of the network to broadcast storms(badai). The smaller the VLAN group, the smaller the number of users affected(dipengaruhi) by broadcast traffic activity within the VLAN group. You can also assign VLANs based on the application type and the number of applications broadcasts. You can place users sharing a broadcast-intensive application in the same VLAN group and distribute(menyalurkan) the application across the campus.

 

3.4.3 How VLANs can improve network security

The use of LANs has increased at a very high rate(harga) over the past several years. As a result, LANs often have confidential(rahasia), mission-critical data moving across them. Confidential(rahasia) data requires security through access restriction(batasan). One problem of shared LANs is that they are relatively easy to penetrate(ditembus). By plugging in to a live port, an intrusive user has access to all traffic within the segment. The larger the group, the greater the potential access. One cost-effective and easy administrative technique to increase security is to segment the network into multiple broadcast groups that allows the network manager to: Restrict(membatasi) the number of users in a VLAN group Prevent(mencegah) another user from joining(keikutsertaan) without first receiving approval(persetujuan) from the VLAN network management application Configure all unused ports to a default low-service VLAN Implementing this type of segmentation is relatively straightforward(terus terang). Switch ports are grouped together based on the type of applications and access privileges(istimewa). Restricted(batas) applications and resources are commonly placed in a secured(dijamin) VLAN group. On the secured(terlindungi) VLAN, the switch restricts access into the group. Restrictions can be placed based on station addresses, application types, or protocol types. You can add more security enhancements(peningkatan) by using access control lists, which will be discussed in a later chapter. These are especially(utama) useful when communicating between VLANs. On the secured VLAN, the router restricts access to the VLAN as configured on both switches and routers. You can place restrictions on station addresses, application types, protocol types, or even by time of day.

 

3.4.4 How VLANs can save money

Over(diatas) the past several years, network administrators have installed a significant(penting) number of hubs. Many of these devices are being replaced with newer switching technologies. Because network applications require more dedicated(persembahan) bandwidth and performance(hasil) directly(ditunjukkan) to the desktop, these hubs still perform(menyelenggarakan) useful functions in many existing installations. Network managers save money by connecting existing hubs to switches. Each hub segment connected to a switch port can be assigned to only one VLAN. Stations that share a hub segment are all assigned to the same VLAN group. If an individual station needs to be reassigned(ditempatkan kembali) to another VLAN, the station must be relocated(dipindahkan) to the corresponding hub. The interconnected switch fabric(susunan) handles the communication between the switching ports and automatically determines the appropriate(tepat) receiving segments. The more the shared hub can be broken into smaller groups, the greater the microsegmentation and the greater the VLAN flexibility for assigning individual users to VLAN groups. By connecting hubs to switches, you can configure hubs as part of the VLAN architecture. You can also share traffic and network resources directly attached(diberikan) to switching ports with VLAN designations(penunjukan).   Lab Activity In this lab you will learn to display information about current Switch Firmware, learn about switch memory and update options, and how to use a TFTP Server to update a switch to a new version of the Firmware software.     Lab Activity   In this lab you will work with Ethernet Virtual Local Area Networks or VLANs. VLANs can be used to separate groups of users based on function rather than physical location. Normally all of the ports on a switch are in the same default VLAN 1. This lab introduces multi-switch VLANs using trunking.

 

Summary

Now that you completed this chapter, you should have a firm understanding of the following: An Ethernet switch is designed to physically segment a LAN into individual collision domains. A typical LAN is configured according to the physical infrastructure(prasarana) it connects. In a LAN that uses LAN switching devices, VLAN technology is a cost-effective and efficient way of grouping network users into virtual workgroups, regardless (tanpa memperhatikan)of their physical location on the network. VLANs work at Layer 2 and Layer 3 of the OSI reference model. Important to any VLAN architecture is the ability to transport VLAN information between interconnected switches and routers that reside(terletak) on the corporate(berhubungan) backbone. The problems associated with shared LANs and switches are causing traditional LAN configurations to be replaced with switched VLAN networking configurations. The most common approaches(menemui) for logically grouping users into distinct(jelas) VLANs are frame filtering, frame tagging, and frame identification. There are three main types of VLANs: port-centric VLANs, static VLANs, and dynamic VLANs. VLANs provide the following benefits: They reduce administration costs related to solving problems associated with moves, additions, and changes. They provide controlled broadcast activity. They provide workgroup and network security. They save money by using existing hubs.     Threaded(urutan) Case Study     Washington School District(daerah) Project Task: User Requirements, Site Maps, Handling Graphics After this chapter, you will continue studying the TCS Overview for the Washington School District Network Design Project, focusing on the LAN requirements. You should begin work on your school site wiring diagrams (physical topologies). And you will need to learn some basics about graphics file formats and graphics manipulation. You need to complete the following tasks: Familiarize yourself with the LAN sections (and User Counts) of the TCS Overview , including any activities your Instructor assigns. Individually, begin working on your site wiring diagrams. Then discuss them as a group. Understand the different graphic file formats involved in how your Instructor wants you to submit your Web-based TCS Solutions. Apply the CCNA Certification Exam Learning Objectives to your specific design. This will require a paragraph on how the learning objectives relate to your design. Learning objectives can be grouped together for the purpose of explanation(keterangan). In this way, you will be studying for the CCNA Certification Exam as you work through the case study. CCNA Certification Exam Learning Objectives (*** are explicit CCNA Exam objectives; unmarked are knowledge assumed by the exam): VLANs Describe the operation of the Spanning Tree Protocol and its benefits.*** Describe the operation of virtual LANs.***