Information Technology Reference
In-Depth Information
This chapter covers WA N design topics that you need to master for the CCDA exam. It be-
gins by discussing physical WAN technology and WAN topologies used in the enterprise.
Next is a review of remote-access network requirements that are used to design remote-
access networks. The chapter goes on to cover the specifics of VPN design and the differ-
ent connectivity options available for enterprise VPNs and service provider (SP) VPNs.
Next, several backup strategies are explored that are used when designing WANs. Then
the chapter reviews the considerations used in developing WAN architectures, including
the hardware and software options used when selecting components for network designs.
In addition, the design of branch offices is discussed, with a review of several options for
designing different sizes of branch offices.
When selecting a particular WAN technology, you should be familiar with the three major
categories that represent traditional WANs:
Circuit switched:
Data connections that can be brought up when needed and termi-
nated when finished. Examples include ordinary public switched telephone network
(PSTN) phone service, analog modems, and ISDN. Carriers reserve that call path
through the network for the duration of the call.
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Key
To p i c
Leased lines:
A dedicated connection provided by the SP. These types of connec-
tions are point to point and generally more expensive. Time-division multiplexing
(TDM)-based leased lines usually use synchronous data transmission.
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Packet and cell switched:
Connections that use virtual circuits (PVC/SVC) estab-
lished by the SP. Packet-switched technologies include Frame Relay and cell-switched
technologies such as ATM. ATM uses cells and provides support for multiple quality
of service (QoS) classes. The virtual circuits are part of the shared ATM/Frame Relay
SP backbone network. This gives the SP greater flexibility with its service offerings.
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When planning and designing a packet-switched WAN, you should become familiar with
some basic WAN topologies. These WAN topologies include hub-and-spoke, partial-
mesh, and full-mesh topologies, as shown in Figure 7-1.
Hub-and-Spoke Topology
A star or hub-and-spoke topology provides a hub router with connections to the spoke
routers through the WAN cloud. Network communication between the sites flows
through the hub router. Significant WAN cost savings, lower circuit counts, and simplified
management are benefits of the hub-and-spoke topology. In addition, hub-and-spoke
topologies provide WAN hierarchy and can provide high availability through the use of
dual routers at the hub site.
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sent a single point of failure. The hub-and-spoke topology can also limit the overall
