Handbook of Local Area Networks, 1998 Edition:LAN Management
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The Discovery Protocol
A discovery protocol is at the core of this intelligence. The management agent is part of the operating system software and functions as a lower-layer protocol that interrogates adjacent device information. The discovery protocol gathers information about the type of devices in the network, configuration information about the links connecting those devices, and the number of interfaces within each device. Additionally, it updates the management agents within the appropriate devices when a configuration or device change occurs, providing detailed information that allows managers to maintain a low-level connectivity model of the network and construct graphical topology maps.
To assist in this process, core intelligence is used in the operating system to build multilayer topology views by importing discovery protocol information into the topology management application and applying logical configuration data on top of the physical network information. The process result is a core understanding of the network at multiple layers, while serving as the basis for higher-level internetworked switched management applications.
VLAN Management
VLANs streamline workflow by improving communications and reducing administrative costs usually associated with traditional LAN management on shared network segments. VLANs fit well with the way many of today’s companies are structured, based on geographically dispersed organizations and crossfunctional work teams, as shown in Exhibit 7-2-3.
Exhibit 7-2-3. VLAN Configuration Based on User Workflow
When a restructuring or change of job duties requires the move of one or more computer users to a different LAN segment, network administrators must change either the wiring structure, the address tables, or both.
VLANs address one of the biggest management challenges network managers face today: the costly expenses associated with moves, adds, and changes. Usually, users in the same workgroup are connected to the same hub, with each hub segment forming a single physical LAN. Hub segments may be connected by a router, which controls connectivity, distributes bandwidth, and sorts out differing protocols among workgroups.
In a VLAN, by contrast, physical network changes are not required when logical adds, moves, and changes occur. If a user moves from the finance department to the accounts payable department, no physical changes to the switch or end station are necessary. The port is simply reassigned to a different VLAN. Any switch port can be assigned to any VLAN, making the logical grouping of users independent of their physical location.
A VLAN management application for configuring, managing, and monitoring interconnected switches and routers should include:
• Graphical mapping utilities for viewing and configuring logically defined workgroups.
• Drag-and-drop, port-level configuration options for assigning users to VLANs.
• Automated link assignment settings for managing VLANs campuswide.
• Integration with common SNMP management platforms for consolidating system resources.
• Detailed reporting functions for maintaining audit trails.
• Detection and reporting of misconfigured links.
For example, network administrators at a US software development firm rely on switches within their main campus network to increase network throughput and simplify routine maintenance tasks. They use an intuitive, drag-and drop application that enables network administrators to design and manage VLANs across physically linked LAN switches. This allows them to configure their networks based on related user groups rather than geographic location.
According to a network manager at the software development firm, the tool saves network administrators upwards of 10 hours per week that they used to spend connecting switch ports, updating host files, and moving equipment around. This makes it easy to continually reshuffle people to keep them close to the other people with whom they need to interact.
Managing Switched-Based Traffic
User sophistication has increased as quickly as the capacity of computers, resulting in an onslaught of resource-hungry, network-enabled applications. Something as common as a data warehouse can have tremendous ramifications on network traffic and throughput, both from increased user query activities and periodic bulk data transfers. Without proper network planning and traffic management techniques, even a well-designed network can experience bottlenecks. It is important for network managers to profile the network usage, traffic patterns, and overall demands on the network. Without this type of tangible traffic analysis, changes to the network are performed based on guesswork. This often leads to costly changes that have no effect on correcting the source of the problems.
Successful traffic management, coupled with the ability to apply real-time analysis and diagnostic tools to quickly rectify problems, is critical. This capability allows network managers to predict how new applications will affect usage levels and traffic patterns. They can also detect local problems on a LAN segment before the overall performance of the network is impacted.
An effective traffic management application maximizes the usefulness of switching platforms by making traffic information available to the network administrator on each virtual segment. Using such an application, administrators can target specific network segments that are causing problems, as well as set alarms to detect potential problems before they occur.
For example, a traffic management application can use RMON agents to detect excessive traffic between two VLANs. Information is collected from RMON agents in network switches and monitoring probes. With this data in hand, network managers can view enterprisewide traffic for any segment or ring from the link, network, transport, or application layer. A decoding capability lets them determine if a particular protocol is responsible for excessive traffic, indicating that traffic from a particular node is the source of problems.
A traffic management application can also send traps to network management platforms. Proactive alarms can be triggered when a preset threshold is exceeded for any MIB variable. This allows administrators to proactively monitor the network and respond before excessive traffic levels result in a bottleneck. Performance and fault management are simplified through the use of views, alarms, and remote packet capture, and packet filters let users monitor all seven layers of network traffic. Summary reports of important traffic statistics offer at-a-glance views of network activity and potential problems.
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