Increased user demands and complex
applications have forced network designers to focus on the actual
traffic patterns in the network. Networks can no longer be divided
into subnetworks based only on the number of users. The emergence of
enterprise servers that run applications serving all users also have
a direct effect on the load across the network. A higher traffic
load across the entire network results in the need for more
efficient routing and switching techniques. In the new campus model,
traffic patterns dictate the placement of the services required by
the end user. To service the local traffic, Layer 2 switches are
moving to the edge of the network and into the wiring closets. These
switches connect end-user devices and servers into a common
workgroup. Services can be separated into three separate
categories:
- Local services
- Remote services
- Enterprise services
A local service is one where the
entities that provide the service reside on the same subnet, and
therefore, the same virtual network as the user. Local services
remain in specific areas of the network. Traffic to and from local
services is confined to links between the server, the switches, and
the end users. Local traffic does not enter the network backbone or
pass through a router, as you see in Figure .
A remote service is an entity that may be
geographically close to the end user, but is not on the same subnet
or VLAN as the user. Traffic to and from remote services may or may
not cross the backbone. However, because these services are remote
to the requesting end user, requests for the remote services will
have to cross broadcast domain boundaries. Therefore, switches must
connect to Layer 3 devices to allow for access to remote services.
Enterprise services are services
common to all users. Examples of enterprise services are e-mail,
Internet access, and videoconferencing. Because all users need to
access enterprise services, these servers and services exist within
a separate subnet placed close to the backbone, as shown in Figure .
Because enterprise services exist outside of the broadcast domain of
the end user, Layer 3 devices are required to access these services.
The enterprise services may or may not be grouped by Layer 2
switches.
Placing the enterprise servers close
to the backbone ensures the same distance from each user; however,
this also means that all traffic going to an enterprise server will
indeed cross the network backbone.
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