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Cisco Network Topology and Design

Chapter Description

Explore design issues related to overall network topology with this sample chapter from CCIE Professional Development: Large-Scale IP Network Solutions by Cisco Press.

Access Design

In most cases, an access router serves a large number of customers. With modern access technology, this number can reach the thousands. As a result, resilient connectivity to the distribution routers is recommended. This may be accomplished using a self-healing LAN technology, such as FDDI. Alternatively, as with the connectivity between distribution and backbone routes, this may involve the use of redundant LAN switches. If the access router is the only node in a small POP, redundant WAN connections to the nearest DC are an option.

The design of the access topology is generally a choice of WAN technology between the CPE and the access router. For redundancy or load-sharing purposes, two or more links may be homed into the same access router or possibly onto different access routers. This is an issue of provider policy and capabilities.

Although the topology of the access network is relatively simple, it is here that the "policing" of customer connections, in terms of traffic rates and accounting, QoS, and routing policy, occurs. The configuration and maintenance must be executed carefully. The consequences of a router misconfiguration can be severe.