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CISCO INTERNETWORK DESIGN EXAM OBJECTIVES COVERED IN THIS CHAPTER:
As the most popular desktop operating environment, Windows holds a substantial position of prominence in modern network designs. Yet this chapter truly encompasses a great deal more than just networking with Windows-based systems and the design criteria for these environments. It also incorporates information regarding the other major desktop protocolsAppleTalk and IPXas they relate to each other and as they compare to Windows-based systems.
This chapter also discusses the NetBIOS protocol, the foundation of the Windows-based operating systems. NetBIOS-based networks are found in the following operating systems/environments:
Also identified in this chapter is the importance of the interoperation of NetBIOS with other protocols. For example, NetBIOS, as a foundation for Windows-based networks, was originally designed to operate over NetBEUI, a non-routable protocol. Both IPX and TCP/IP have been enhanced to support NetBIOS encapsulation, greatly enhancing the protocols incorporation into modern large-scale networks and providing designers with a means to support NetBIOS without NetBEUI.
As mentioned in previous chapters, all of the desktop protocols were designed around the client/server model (although Macintosh and Windows platforms could service both functions). This design includes the use of LANs with multiple hosts and typically operates as a single broadcast domain. The client is responsible for locating the serverthe GNS process in IPX, for exampleand the protocols rely on broadcasts, which adds substantially to the network load.
Unlike NetBEUI, the original underlying protocol for NetBIOS, the other common desktop protocols use routable Layer 3 structures. In Novell networks, these are NCP and SPX packets on top of IPX packets; in Macintosh environments, these are the protocols that comprise AppleTalk. As such, desktop protocols are defined at Layer 3 and above in reference to the OSI model. Most designers work with the desktop protocols as suites rather than addressing the facets of each individual protocol in the stack. This works from an architecture standpoint, as the protocols were designed to operate together, and most desktop issues may be isolated to the access layer of the hierarchical model.
The issue of broadcasts in designs has been raised throughout this book. This is predominately due to the client workstation impact of broadcasts and the overhead on the individual processors caused by receipt of those datagrams. This is not an issue with unicasts, where the destination station performs all processing required by the upper-layer protocols. However, in broadcasts, all nodes in the broadcast domain must process the packet, and the majority of the nodes will discard the information, resulting in waste.
Broadcasts may be measured using two methods: broadcasts per second and broadcasts as a percentage. A good metric is dependent on the number of broadcasts per second100 being a recommended guideline. Unfortunately, most networkers learned a long time ago that 10 percent broadcast traffic was a threshold and that networks were healthy so long as traffic remained below that value. Yet in practice, using a percentage as a metric is too limited for a number of reasons:
The NetBIOS protocol is traditionally mapped to the session layer of the OSI model. It relies on names and name queries to locate resources within the network. Thus, network designers should keep the following in mind when architecting Windows-based networks:
Groups of computers in Windows-based networks may be organized in one of two logical clusters: workgroups and domains. These groupings are not unlike the zone function in AppleTalk, but there are a few differences.
The basic grouping of machines is a workgroup. Workgroups may be created by any set of workstations, and the cluster does not participate in any authentication or central administration process. Each machine in a work-group may permit access to its resources, and any machine may join the workgroup. Thus the security level in workgroups is quite low, and the model is only suited to small organizations when administration is shared among all the users.
Domains, more formal groupings of computers than workgroups, significantly change the level of security offered to the organization. First, domains are administered via a Primary Domain Controller (PDC). There can be only one PDC for the domain, and it is authoritative for that domain. To provide redundancy, the PDC may be supported by any number of Backup Domain Controllers (BDCs). In practice, most organizations deploy only one or two BDCs in their configurations, although it may be warranted to deploy more. BDCs are typically installed in remote locations to speed local login and authentication while retaining a centralized administrative model.
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