Troubleshooting guide

CHAPTER
4-1
ATM and Layer 3 Switch Router Troubleshooting Guide
OL-1969-01
4
Example Network
This chapter uses an example network to illustrate hardware configuration problems and configuration
troubleshooting. The example network describes the most common connections you need to
troubleshoot, and enables you to apply your own enterprise network configuration to the examples.
This chapter contains the following sections:
• Network Hierarchy, page 4-1
• Example Networks, page 4-2
Network Hierarchy
In a well-formed hierarchical network, there are three easily defined layers, traditionally referred to as
the access, distribution, and core layers.
In an enterprise network, each layer provides different functions. Because these layers are not always
recognized by their traditional names, the names have been modified to access or workgroup,
distribution or policy, and core or backbone.
The access or workgroup layer connects users. Other functions of this layer are shared bandwidth,
switched bandwidth, MAC-layer filtering, and micro segmentation. LAN switches, such as the
Catalyst 5000 and Catalyst 6000 family of switches, exist most commonly in this layer of the network.
The distribution or policy layer performs the complex, CPU-intensive calculations such as filtering,
access lists, inter-VLAN routing, Group Multicast Protocol (GMP), broadcast and multicast domain
definition, and address or area aggregation. This layer might also contain the local servers. Routers,
switch routers, and occasionally LAN switches reside in the distribution layer.
The core or backbone layer is the backbone of the network. It is high-speed and concerned with quick
traffic switching. It does not get involved in expensive packet manipulation. In the following example
network, ATM connections function together as the core backbone, and Fast Ethernet and Gigabit
Ethernet connections function together as the redundant backbone core. The central servers might also
be attached to the high-speed backbone in the core. Switch routers, high-speed routers, and occasionally
LAN switches can be found in the core.