methods Verifies packet expiration and
updates accordingly Processes and responds to any
option information Updates forwarding statistics in
the MIB Applies security and policy controls, if
required Provides optimal path determination
Can (if it is a sophisticated modular type) support a wide
variety of media types and port densities Has the
ability to support QoS Has the ability to support VoIP
and inline power requirements Because it is designed
to handle high-performance LAN traffic, you can place a
multilayer switch anywhere within the network, thereby
replacing traditional switches and routers cost-effectively. In
most cases, a lower cost access switch connects end users and
multilayer switches are used in the distribution and core
layers of the campus network model.
Content 1.1
Introducing Campus Networks 1.1.7 Issues
with Multilayer Switches and VLANs in a Non-Hierarchical
Network Multilayer switches combine switching and routing
on a single hardware platform and can enhance overall network
performance when deployed properly. Multilayer switches provide
very high-speed Layer 2 and Layer 3 functionality by caching
much of the forwarding information between sources and
destinations. However, the following issues exist when a
multilayer switch is deployed in an improperly designed
network: - Because multilayer switches condense the
functions of switching and routing in a single chassis, they
can create single points of failure if redundancy for these
devices is not carefully planned and implemented.
-
Switches in a flat network are interconnected, creating many
paths between destinations. If active, these potential
redundant paths create bridging loops. To control this, the
network must run a STP. Networks that use the IEEE 802.1D
protocol may experience periods of disconnection and frame
flooding during a topology change.
- Multilayer switch
functionality may be underutilized if a multilayer switch is
simply a replacement for the traditional role of a router in a
non-hierarchical network.
Content 1.1
Introducing Campus Networks 1.1.8 The
Enterprise Composite Network Model The Enterprise Composite
Network Model (ECNM) can be used to divide the enterprise
network into physical, logical, and functional areas. These
areas allow network designers and engineers to associate
specific network functionality on equipment based upon its
placement and function in the model. The ECNM provides a
modular framework for designing networks. This modularity
allows flexibility in network design and facilitates ease of
implementation and troubleshooting. The hierarchical model
divides networks into the building access, building
distribution, and building core layers, as follows:
- Building access layer: Grants user access to network
devices. In a network campus, the building access layer
generally incorporates switched LAN devices with ports that
provide connectivity to workstations and servers. In the WAN
environment, the building access layer at remote sites may
provide access to the corporate network across WAN
technology.
- Building distribution layer:
Aggregates the wiring closets and uses switches to segment
workgroups and isolate network problems.
- Building
core layer: Also known as the campus backbone submodule,
this layer is a high-speed backbone and is designed to switch
packets as fast as possible. Because the core is critical for
connectivity, it must provide a high level of availability and
adapt to changes very quickly.
An enterprise campus
is defined as one or more buildings, with multiple virtual and
physical networks, connected across a high-performance,
multilayer-switched backbone. The ECNM contains these three
major functional areas: - Enterprise campus:
Contains the modules required to build a hierarchical, highly
robust campus network that offers performance, scalability, and
availability. This area contains the network elements required
for independent operation within a single campus, such as
access from all locations to central servers. The functional
area does not offer remote connections or Internet
access.
- Enterprise edge: Aggregates
connectivity from the various resources external to the
enterprise network. As traffic comes into the campus, this area
filters traffic from the external resources and routes it into
the enterprise campus functional area. It contains all the
network elements for efficient and secure communication between
the enterprise campus and remote locations, remote users, and
the Internet. The enterprise edge would replace the
Demilitarized Zone (DMZ) of most networks.
- Service
provider edge: Represents connections to resources external
to the campus. This area facilitates communication to WAN and
Internet service provider (ISP) technologies.
Content 1.1 Introducing Campus Networks
1.1.9 Benefits of the Enterprise Composite Network
Model To scale the hierarchical model, Cisco introduced
ECNM, which further divides the enterprise network into
physical, logical, and functional areas. ECNM contains
functional areas, each of which has its own building access,
building distribution, and building core (or campus backbone)
layers. ECNM has these features: - It is a deterministic
network with clearly defined boundaries between modules. The
model also has clear demarcation points so that the designer
knows exactly where traffic is located.
- It increases
network scalability and eases the design task by making each
module discrete.
- It provides scalability by allowing
enterprises to add modules easily. As network complexity grows,
designers can add new functional modules.
- It offers
more network integrity in network design, allowing the designer
to add services and solutions without changing the underlying
network design.
Figure shows the benefits that ECNM
offers for each of the submodules where it is implemented.
Content 1.1 Introducing Campus
Networks 1.1.10 Describing the Campus
Infrastructure Module The enterprise campus functional area
includes the campus infrastructure, network management, server
farm, and edge distribution modules. Each module has a specific
function within the campus network: - Campus
infrastructure module: Includes building access and
building distribution submodules. It connects users within the
campus to the server farm and edge distribution modules. The
campus infrastructure module is composed of one or more floors
or buildings connected to the campus backbone submodule.
- Network management module: Performs system logging,
authentication, network monitoring, and general configuration
management functions.
- Server farm module:
Contains e-mail and corporate servers providing application,
file, print, e-mail, and Domain Name System (DNS) services to
internal users.
- Edge distribution module:
Aggregates the connectivity from the various elements at the
enterprise edge functional area and routes the traffic into the
campus backbone submodule.
The campus infrastructure
module connects users within a campus to the server farm and
edge distribution modules. The campus infrastructure module
comprises building access and building distribution switches
connected through the campus backbone to campus resources. A
campus infrastructure module includes these submodules:
- Building access submodule (also known as building access
layer): Contains end-user workstations, IP phones, and
Layer 2 access switches that connect devices to the building
distribution submodule. The building access submodule performs
services such as support for multiple VLANs, private VLANs, and
establishment of trunk links to the building distribution layer
and IP phones. Each building access switch has connections to