Chapter 1. Large Enterprise Networks
| Modern networks are divided, in terms of their operations, into essentially two main categories: enterprise and service provider (SP). In this book we focus on the principles and concepts of managing large enterprise networks. Examples of such networks are government departments, global corporations, and large financial/healthcare organizations. Most such enterprises employ the products and services of SP networks, so we try to balance the discussion by including some general comments about managing SP networks as well. It is in the latter network type that we tend to describe Multiprotocol Label Switching (MPLS), a widely deployed technology. In passing, we mention that MPLS is also finding its way into large enterprise WANs. An important point to note is that network management is a distinct and separate discipline from both enterprise and SP networking. For this reason, our study of enterprise, SP, and MPLS network management should be seen merely as applications of network management technology. As we'll see, many elements of network management are common across all such application areas. We have six main aims:
We set the scene by describing in general terms some of the components of large enterprise networks. These networks are big and geographically dispersed (often spanning many countries ), have lots of legacy equipment, and are hard to managescalability is an issue affecting both their manageability and usability. After introducing the general area, we begin our discussion of network management. Generally , enterprise networks are owned by a single organization, such as IBM, federal government bodies, and financial institutions. These networks exist to provide data and telecommunications services to employees , customers, and suppliers. Services can include:
Enterprise networks achieve these and other services by deploying a wide variety of different technologies and systems. Some services encompass several technologies, such as voice-over-IP (VoIP) [Tanenbaum2003], which can be transported over a WAN link to achieve toll bypass or migration away from overlay networks (for voice, video, and data). An enterprise [2] uses its network as a means of providing or improving business processes and saving money rather than as a vehicle for profit. This mindset influences enterprise decisions to deploy solutions like VoIP telephony. The guiding principle is service enhancement and business advantage rather than reductions in spending (though the latter is also extremely important). In fact, some global organizations are so big that they can often negotiate reduced tariffs with their local telecommunications carrierin many cases a quicker and easier way to save money than rolling out expensive, complex, new technology. It may be more important for an organizational department, such as a provider of frontline PC support, to direct a minimum of incoming phone calls to voicemail. This can influence the decision to deploy in-building mobile telephony (e.g., IEEE 802.11 a/b, DECT in Europe) so that call handling is not restricted to the desk phone. In other words, service levels are enhanced because calls are less frequently routed to voicemail.
Figure 1-1 illustrates a typical simplified enterprise network. Figure 1-1 is highly simplified in order to give us a flavor of enterprise networking issues. Real enterprise networks tend to feature additional technologies, such as Asynchronous Transfer Mode (ATM), VLANs, broadband connections, and redundant configurations. Later (in Figure 1-4) we will see a portion of an enterprise network realized using VLANs. Figure 1-1. Enterprise network functional components. Figure 1-4. VLANs in an enterprise network. All the boxes with bold text and borders in Figure 1-1 provide some type of servicefor example, Voice Service. The connected boxes provide access to the servicefor example, VoIP phones (in the VoIP box). In fact, the network in Figure 1-1 can serve a large, geographically distributed corporate user population. Alternatively, Figure 1-1 might be a corporate headquarters with hundreds of remote branch offices. It's easy to see why the provision and management of enterprise networks are so critical to modern organizations. The networks and systems in Figure 1-1 add value to the organization, and later we'll see how the enterprise network managers (in many cases, IT groups) can play an important role in assisting the developers of network management software. In this way, IT initiatives are closely aligned with broader business objectives [EnterpriseIT]. Also noteworthy (as mentioned above) is the use of IP phones in a LAN environment, reducing the need for legacy PABX equipment and prompting migration to a packet-based infrastructure. The migration to layer 3 mentioned here is discussed in Chapter 2, "SNMPv3 and Network Management," and is a recurring theme throughout the book. One point about Figure 1-1 is that many or all of its components may be repeated on other sites linked to this one via a WAN. These other sites include normal branches of the organization as well as unmanned backup sites. This means that essentially the same corporate services are offered to all employees regardless of their location, whether it is in New York City or the West of Ireland. Many organizations fund this type of arrangement by charging a straight percentage from the revenues of each local site. Also, different sites can offer services, such as audio conference bridges, to other sites. In this case, the site hosting the bridge bills the users dialing into it from remote sites. There are many reasons for using this geographically distributed approach to enterprise network deployment:
Notable features of Figure 1-1 are the incorporation of separate networks for storage (i.e., storage area network, or SAN), WAN, SP networks, and telephony. SANs provide access to data storage facilities. WANs provide access to remote network facilities. SP networks provide Internet access (among other services), and the Public Switched Telephone Network (PSTN) provides access to the global telephony networks (fixed and mobile). Typically, an enterprise will use several service providers, each providing one or more of the above services. The enterprise network enables access to a wide variety of devices and services. The important point about the structure depicted in Figure 1-1 is its flexibility: Large numbers of users can share the corporate, productivity-enhancing services using a wide range of access methods . By this means, an employee working from home can be at least as effective as one based in the office without the need for commuting. Similarly, sales staff can access (e.g., via a VPN) the enterprise network during business trips. Another trend is unified messaging for integrated access to email, voicemail and fax mail messages using an email client. PCs can also be used for access to videoconference broadcasts and even videophone calls. Audio conference calls can also be accessed via unified messaging or by using a desk phone. Some organizations even use broadcast voicemail to make important announcements. Another aspect of enterprise networks is linkages between desktop calendars and the reservation of meeting rooms. Rooms are booked and invitees are reminded via their email client. Intranets provide official enterprise information channels for employees. Many organizations use intranets for posting important information such as product announcements and corporate media coverage. Another intranet facility is integration of productivity tools such as document management systems. In this sense, the intranet becomes just another desktop tool accessible using a Web browser. As we'll see later, the Web browser is often an indispensable part of an NMS. Enterprise data flows can become very complex once extranets and e-commerce are employed. Extranets are parts of intranets that are extended to organizations external to the enterprise, such as software contractors. E-commerce allows for secure financial transactions between external customers and a given organization. The data flows in the latter case feed into various systems, such as finance, stock control, and manufacturing. Other important aspects of maintaining secure enterprise networks include:
Many organizations distribute enterprise software in a centralized fashion, for example, using Microsoft Systems Management Server. This can include defensive procedures such as anti-virus software updates. Likewise, productivity software such as word processors and spreadsheets can generally be updated in the same way. Many end users of enterprise systems tend not to log out, so policies can be applied to host machines that will log the user out after, say, 15 minutes of inactivity. This can be done for security reasons and also in order to update anti-virus software once the user logs back in again. A full virus scan can then occur at night. The important area of software license checking can also be handled remotely to verify that the number of end users who have installed software packages does not exceed the license limit. These various uses of enterprise facilities clearly illustrate the power of the underlying network. Following are some general features of enterprise networks:
Enterprise systems and networks all have individual lifecycles comprised of:
In this book we focus mostly on network operation and management, but the other lifecycle stages are equally important. An example of this is a SAN in which the following steps typically occur:
Growing storage requirements in enterprises can have the effect of reducing backup time windows . This and other storage issues may cause loss of service and require that administrators deal with problems such as:
All of these require some type of reactive (after the problem has occurred) manual intervention. Clearly, there is a relationship between storage planning and the incidence of storage capacity being exceeded. The same is true for the ever-increasing storage demands of application software. Network administrators need tools to help them balance these dynamic requirements. Where possible, the NEs should be engineered to facilitate this type of advanced management. In conjunction with NE-resident self-management capabilities, there is a need for high-quality management systems. The latter should then provide features that match the organizational workflows (broadly speaking, these are plan, construct, and operate ). Another very common enterprise technology is the VLAN. Many organizations employ VLANs in order to provide a switched layer 2 infrastructure with designated broadcast domains. A broadcast domain is a set of layer 2 devices with a defined boundary (typically an IP router) beyond which broadcast traffic will not flow. For example, an organization could group the NEs on each floor of a building into a different VLAN (i.e., broadcast domain). All of these floor-level VLANs could then be connected to a single high-speed switch that is in turn connected to another set of VLANs. One of the merits of VLANs is scalabilityto add more devices, you can just create another VLAN. This helps to avoid the problem of running out of broadcast domain capacity on a single medium (such as a large Ethernet network). Building and operating VLANs can be carried out using either an element management system (EMS) or an NMS. A typical workflow for adding a new PC to VLAN X is as follows :
As far as possible, the NMSor EMS in this caseshould facilitate this type of workflow. For example, when adding a port to a VLAN, only options appropriate to that hardware should be presented. So, if a port does not support 802.1Q, then the EMS/NMS should not present an option to set a VLAN ID. This information can be acquired by the EMS/NMS (via automatic dialog with the NE) and greatly assists in managing such devices. There is a downside to the rich environment provided by enterprise networks. They are expensive to build and run, and they require skilled maintenance and support personnel. Traditionally, the network support effort (excluding PC support) has been divided into two camps, data networking and telecommunications, but these two areas are rapidly converging. PABX technology is gradually being phased out and replaced by server-based solutions [CiscoVoIP]. Multiple incompatible networks for voice, video, and data are gradually being migrated onto a packet-based infrastructure. Many organizations seek to centralize servers in secure locations and then lease WAN lines from there to branch offices and divisions. This reduces remote site support but increases dependency on communications lines, an increasingly cheap commodity [GlobalCross2002]. Services are resolving down to the process of transporting bits from location X to location Y over a single physical network.  |
EAN: 2147483647
Pages: 150