Exam Essentials

Remember the common switching modes used in network designs. Process switching is a preferred mode in most designs. Using the route table, process switching forwards all subsequent packets out the same interface as the first. Fast switching is on by default on the lower end routers such as the 2500 and 4000 series and is an enhancement when processor and interface limitations are present. Autonomous, silicon, optimum, distributed, and NetFlow switching modes are used primarily in higher end Cisco routers and are designed to move large amounts of network packets efficiently.

Be familiar with the different WAN design solutions. Designing for availability, bandwidth, cost, management, and application and routing protocol needs requires familiarity with available WAN solutions. WAN bandwidths come in all speeds, from 56K analog modems to T3 and beyond. Dial-up capability, leased lines and packet-switched services are solutions to specific design needs.

Remember the different WAN protocols and their intended use. SDLC was developed and used by IBM in their mainframe network designs. HDLC is a derivative of SDLC and is the default WAN protocol on Cisco routers. ISDN is a popular, moderate-speed, or backup solution to Frame Relay, which offers high speed and availability.

Understand the many configuration needs of Frame Relay. DLCIs, LMIs, and subinterfaces are all configuration needs of Frame Relay. DLCIs are assigned by the provider and are only locally significant to a connection’s configuration. LMIs can now be autosensed by Cisco’s IOS version 11.2 and greater, but Cisco is the default LMI type. Subinterfaces offer a design solution to address configuration needs when working with partial mesh networks.