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Example Network

Example Network

This chapter describes the example network that illustrates the hardware configuration problems and configuration troubleshooting in this guide. The example network also describes the most common connections needed to troubleshoot. Providing one network example and using that network example exclusively eliminates confusing network names, addresses, and redundant descriptions. By using a single example, you can apply your own enterprise network configuration to the examples.

Note Each network node has an abbreviated name that appears in the prompt using the following format; building, floor, equipment type, number. For example the prompt, AdminFl1Ls1# refers to the administration building, floor 1, LightStream 1010 switch, number 1.

Troubleshooting Engine

Cisco provides a troubleshooting engine on the World Wide Web for registered users to help solve common problems involving hardware, configuration, and performance at the following URL: http://www.cisco.com/diag/te_start.shtml

Network Hierarchy

In a well-formed hierarchical network, there are three easily defined layers, traditionally referred to as the access, distribution, and core layers. (See Figure 3-1.)


Figure 3-1: Network Hierarchy


Each of these layers provides a different function. The layers do not need to exist in clear and distinct physical entities, but the functionality needs to exist in an enterprise network. To help understand these functional layers, the traditional layers have been modified to access or workgroup, distribution or policy, and core or backbone.

The main function of the access or workgroup layer is to connect users. Other functions represented by this layer are shared bandwidth, switched bandwidth, MAC-layer filtering, and micro segmentation. LAN switches, for example the Catalyst 5000 and 5500 switches, are most commonly seen in this layer of the network.

The distribution or policy layer performs the policy-based operations. It performs the complex, CPU-intensive calculations such as filtering, access lists, inter-VLAN routing, GGMP, broadcast and multicast domain definition, and address or area aggregation. This layer may also contain the local servers. ATM switches and routers reside in the distribution layer, and sometimes LAN switches may reside here as well.

The core or backbone layer is the backbone of the network. It should be high-speed and concerned mainly with switching traffic as quickly as possible. It should not get involved in "expensive" packet manipulation. ATM connections or Fast Ethernet connections, which functions as a backup, should make up the core backbone. The central servers may also be attached to the high-speed backbone in the core. ATM switches, high-speed routers, and sometimes LAN switches can be found in the core.

Example Network

This section describes a fictitious network that was created to provide a narrative to describe actual problems in troubleshooting ATM switched networks.

Figure 3-1 provides a high-level overview of the campus and remote networks.


Figure 3-2: Example Network Overview


The example network in Figure 3-2 has the following components:

Physical Connections

The example network contains the following physical connections:

Virtual Connection Types

The example network contains the following virtual connections:

The equipment overview of the example network, shown in Figure 3-3, shows the various equipment and the connection types of the network. Each is described in greater detail in subsequent illustrations.


Figure 3-3: Equipment Overview of the Example Network


The engineering building in Figure 3-4, shows the following connections:

Note Each Fast Ethernet distribution switch connection has a redundant link (see Figure 3-5).

Figure 3-4: Engineering Building


The typical floor one wiring closet of the example network, shown in Figure 3-5, shows the following connection examples:


Figure 3-5: Typical Floor 1 Wiring Closet


The typical core switch configuration of the example network, shown in Figure 3-6, illustrates the following connections:


Figure 3-6: Typical Core Switch Configuration


The typical distribution switch configuration of the example network, shown in Figure 3-7, shows the following connection examples:


Figure 3-7: Typical Distribution Switch Configuration to Floor 1


The administration building configuration of the example network in Figure 3-7 provides the following connections:


Figure 3-8: Administration Building Connections


Network Failure Preparation

This section provides a sample of the type of information you need to document for your network. These examples use the information described in the previous sections of the example network.

Logical Network Map

Keep an up-to-date internetwork map that outlines the physical location of all the network devices and how they are connected, as well as a logical map of network addresses, network numbers, and subnetworks.

Implemented Network Protocols

For your network you should have a list of each protocol implemented, a list of the network numbers, subnetworks, zones, areas, and so on that are associated with them.

Routed Protocols

You should have a list of the protocols being routed and a correct, up-to-date router configuration for each router.

Switched Protocols

You should have a copy of each of the protocols being switched and a correct up-to-date copy of each switch configuration. Plus, if there are any filters configured in any of these switches, you should have a copy of these configurations.

External Network Points of Contact

You should have a list of each external network connection and what routing protocol is being used.

Network Baseline

You should have documented normal network behavior and performance so that you can compare current problems with a baseline.


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