Designing WANs
Internetwork Design Guide
1-4
Traditionally, Layer 2 switching has been provided by LAN switches, and Layer 3 networking has
been provided by routers. Increasingly, these two networking functions are being integrated into
common platforms. For example, multilayer switches that provide Layer 2 and 3 functionality are
now appearing in the marketplace.
With the advent of such technologies as Layer 3 switching, LAN switching, and virtual LANs
(VLANs), building campus networks is becoming more complex than in the past. Table 1-1
summarizes the various LAN technologies that are required to build successful campus networks.
Cisco Systems offers product solutions in all of these technologies.
Table 1-1 Summary of LAN Technologies
Network designers are nowdesigningcampus networksbypurchasing separate equipment types (for
example, routers, Ethernet switches, and ATM switches) and then linking them together. Although
individual purchase decisions might seem harmless, network designers must not forget that the entire
network forms an internetwork.
It is possible to separate these technologies and build thoughtful designs using each new technology,
but network designers must consider the overall integration of the network. If this overall integration
is not considered, the result can be networks that have a much higher risk of network outages,
downtime, and congestion than ever before.
Designing WANs
WAN communication occurs between geographically separated areas. In enterprise internetworks,
WANs connect campuses together. When a local end station wants to communicate with a remote
end station (an end station located at a different site), information must be sent over one or more
WAN links. Routers within enterprise internetworks represent the LAN/WAN junction points of an
internetwork. These routers determine the most appropriate path through the internetwork for the
required data streams.
WAN links are connected by switches, which are devices that relay information through the WAN
and dictate the service provided by the WAN. WAN communication is often called a service because
the network provider often charges users for the services provided by the WAN (called tariffs). WAN
services are provided through the following three primary switching technologies:
LAN Technology Typical Uses
Routing technologies Routing is a key technology for connecting LANs in a campus network. It can be
either Layer 3 switching or more traditional routing with Layer 3 switching and
additional router features.
Gigabit Ethernet Gigabit Ethernet builds on top of the Ethernet protocol, but increases speed ten-fold
over Fast Ethernet to 1000 Mbps, or 1 Gbps. Gigabit Ethernet provides high
bandwidth capacity for backbone designs while providing backward compatibility for
installed media.
LAN switching technologies
• Ethernet switching
• Token Ring switching
Ethernet switching provides Layer 2 switching, and offers dedicated Ethernet
segments for each connection. This is the base fabric of the network.
Token Ring switching offers the same functionality as Ethernet switching, but uses
Token Ring technology. You can use a Token Ring switch as either a transparent
bridge or as a source-route bridge.
ATM switching technologies ATM switching offers high-speed switching technology for voice, video, and data. Its
operation is similar to LAN switching technologies for data operations. ATM,
however, offers high bandwidth capacity.
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