Network Design - Logical PlanningBefore you can begin to design a physical network, however, we first must determine your needs. What services must be provided to your user community? What are the resources you'll need? If you have to compromise, what will it take to satisfy the most users or to provide the more important services? You then will have to take into account network protocols, applications, network speed, and, most important, network security issues; each of these figures into a network's logical design. Another important factor your management will probably force you to consider is cost - you can't forget the budget. These factors make up the logical design for your network. You first should decide what you need and what it will take to provide for those needs. If you are creating a new network and purchasing new applications, you will probably spend most of your time considering the licensing and other financial costs (training users, network personnel, and so on). If you are upgrading older applications, several other factors come into consideration. Many applications that were coded using COBOL, BASIC, FORTRAN, and other languages that helped jumpstart the computer age may have built-in network functionality based on older proprietary network protocols. If this is the case with your network, you have to consider several things. What will it cost to update thousands of lines of code (or more) to more modern versions of the same programming language? What will it cost to upgrade these programs to newer object-oriented languages? To save money, can you upgrade part of your network and use gateway hardware/software to connect to older network components? Because of the costs associated with coding applications that were created many years ago, and the expenses that will be required to update them to modern programming languages, you may be forced to maintain legacy applications for a few years while replacement applications are designed and created. You may find a packaged application that can be used to replace older programs. This problem will apply mostly to proprietary computer architectures, instead of Windows or Unix platforms. If you can simply make minor changes and compile the source code so that it will run on a newer operating system, your costs will be much less than if you have to re-create the applications your users need from scratch. Another cost associated with upgrading to new programs is training users and help-desk personnel. Planning a Logical Network DesignWhen you plan a logical network design, you can start from one of two places. You can design and install a new network from scratch, or you can upgrade an existing network. Either way, you should gather information about several important factors before you begin the logical design. For example, depending on the services that will be provided to clients, you might need to analyze the possible traffic patterns that might result from your plan. Locate potential bottlenecks and, where possible, alleviate them by providing multiple paths to resources or by putting up servers that provide replicas of important data so that load balancing can be provided. The following are other factors to consider:
A hot topic in many companies revolves around just how important it is to let all users have unlimited access to the Internet. If users need to exchange email with vendors, outside consultants, or customers, for example, then you should be sure to send this traffic through a content filter or firewall, and use virus-protection software to detect and prevent malicious code or virus-infected attachments. Applications such as FTP allow users to send or receive files from remote systems. Can you trust each employee to use this application without abusing it? From a security point of view, it is usually considered very improper to allow any new application to be loaded on any computer-desktop or server-without first submitting the application to testing to ensure that is necessary and is not a security risk. Don't leave any backdoors into or out of your network.
Who Are Your Clients?This seems like a very simple question. However, I'm not saying, "What are your clients' names and how well do you know their children?" I am referring instead to your knowledge of the job descriptions for the users on the network. You need to assess work patterns for various departments so that you can appropriately place servers, high-bandwidth links, and other such things in the appropriate physical location of the network. If most of the network traffic you expect to see will come from the engineering department, you'll need to provide that department with a large data pipe. What Kinds of Services or Applications Will the Network Offer?Of course, everyone knows that the most important function of a network today is to support multiuser gaming. Seriously, though, you need to make a list of the kinds of applications currently in use, as well as a list of those requested by users. Each application should have a written risk assessment document that points out potential security problems, if any. Typical network applications today include FTP, telnet, and, of course, browsing the Web. There are "secure" versions of these applications and there are versions that leave a door wide open into your network. Whatever list of applications you chose to support over the network, keep in mind two things:
A commonly overlooked method for getting data files out of a network and onto the Internet is to simply send the files as an attachment to an email. So if you think you've blocked file transfers by disabling FTP access through the firewall, this example should show that you really do need to do a thorough evaluation of any new application or service you will allow on the network. New applications should be justified with facts that show why they are needed. If an existing application can be used to accomplish the same goal, why do you need another application? Should you retire the older application and use a newer one? Pay attention to the details. And don't forget to test new applications to ensure that they perform as expected. The same goes for older applications-will they work on the new or upgraded network? Lastly, do you monitor network usage? Do you want to permit users to spend their days browsing the Net, or checking personal email while at work? Many companies have policies that apply to using the telephone for personal business. Do you overlook this situation when giving users email capability? Are you preventing access to sites that are obviously not business-related? What Degree of Reliability Do I Require for Each Network Link?Just how much downtime is acceptable? For most users, the answer would be zero. Important components of your network, such as file servers, should have fault tolerance built in from the bottom up. In large servers, you'll find dual-redundant power supplies (each connected to a separate UPS), and disk arrays set up using RAID techniques to provide for data integrity in the event that a disk goes south. If a link between two offices needs to be up 100% of the time, you should plan for multiple links between the two sites to provide a backup capability. In this case, you also can justify the cost of the extra link by using load balancing so that network response time is improved. And, if you are using multiple links to remote sites, it's always a good idea to have more than a single path to the site. At one site this author worked at, there were redundant power lines bringing electricity into the site-side-by-side. If a tree falls, will it bring down one or both of those power lines? Note In addition to dedicated links between sites, the use of Virtual Private Networking (VPNs) is becoming a popular method for connecting to remote sites. The advantages of using a VPN are that you can send data across the Internet, which is less expensive than using a dedicated link, and mobile users can also use a VPN connection to connect to your network as they move from place to place. The only problem with this approach is that a remote site, as well as your main site, should use two ISPs to ensure that if one goes down, you still have a connection to the Internet. For a mobile user, this can be problematic if using an Internet service provided by the hotel. You can solve this problem by giving your users access to two different nationwide ISPs. Another technology that can be used to provide an extra layer of redundancy, as well as high-speed access to storage devices, is the Storage Area Network (SAN). A SAN is a network that is separate from the LAN and contains only storage devices and servers that need to access those devices. Because the network bandwidth is not shared with LAN users, multiple servers can access the same storage. If one server fails, other servers can be configured to provide redundant access to the data. Also, the same RAID and other redundancy techniques used for storage devices that are directly attached to a server (such as the SCSI hardware and protocols) can be used on a SAN. The old saying "If it ain't broke, don't fix it" doesn't apply to networks. You should always be proactively looking for potential single points of failure and doing something to fix them. By building redundancy into the network design at the start, you'll save yourself a lot of grief in the future. It's Virtually Universal: TCP/IPFor all practical purposes, the standard LAN protocol today is TCP/IP. This is partly due to the rapid growth of the Internet, and the necessity of most businesses of having a Web presence, as well as the large number of vendors that have adopted this protocol suite. If your LAN is still using an older proprietary network protocol, you should seriously consider what it would take to upgrade to TCP/IP. Currently, TCP/IP version 4 is the most widely used protocol. In the future you can expect that the next version (IPv6) will start to find its way from the core of the Internet out to the edge, where your network resides. While technologies such as Network Address Translation (NAT) are widely employed to remedy the problem associated with the limited address space provided by IPv4, IPv6 will enable a much larger address space. Combine that with Network Address Translation, and the long-term bets are going to be on IPv6, or possibly some of the features that are part of IPv6. In addition to giving you a larger address space, IPv6 includes other important features. Those that will affect your network the most are security mechanisms, which will only become more important as Internet commerce continues to grow. There is one very important reason you should consider TCP/IP as a LAN protocol: There are more trained professionals knowledgeable in TCP/IP than any other LAN protocol at this time. If your network is composed of several operating systems, from Windows to NetWare to Unix and Linux, then the bottom line is that TCP/IP is the lowest common denominator that will allow the easiest connectivity and interaction between all of these. Even Microsoft's now-legacy NetBIOS/NetBEUI protocols have been adapted to run over TCP/IP. Other LAN/WAN ProtocolsThe distinction between LAN and WAN (wide area networking) protocols is beginning to blur. Ethernet was once considered to be a LAN protocol. As time has passed, other technologies, such as Token-Ring, have become minor players in the LAN world. Yet the opposite is true of Ethernet. It has grown from a modest specification endorsed by Intel, DEC, and other vendors, such that it now can be considered a WAN protocol. The capabilities introduced by current LAN technologies are beginning to erode the differences between a LAN and a MAN (metropolitan area network). When the fourth edition of this book was published, Gigabit Ethernet was starting to fall into the inexpensive range of network topologies. That trend has continued and now 10Gigabit Ethernet (10GbE) is frequently being used in enterprise data centers. Today you may be using 100BASE-T for connecting client computers to the network, and Gigabit Ethernet to connect network segments via the network backbone. In some cases your network might even be exclusively based on 10GbE. What does this mean to a network administrator today? With 10Gigabit Ethernet, you can use TCP/IP not only to create a local area network backbone, but to extend that reach to a metropolitan area network. And because TCP/IP is so intertwined with Ethernet, you can achieve an end-to-end MAN link that uses TCP/IP over faster Ethernet connections. Instead of employing more expensive solutions, such as SONET, you can now connect branch offices in the same geographical area using just TCP/IP. You may not have to worry about installing expensive equipment used by SONET and other typical MAN protocols. Still, for the long haul-for example, between different cities-other protocols such as ATM and Frame Relay will come into play. |
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The most common IT mistakes businesses can make...1.) Not having an IT plan or budget for the year - our workplaces are now inseparably reliant on IT. When a businesses IT fails ..... [more] |
