two devices. Layer 2 switches are used in the
access layer. Web Links Understanding Network Models –
The Cisco Network Design Model http://www.2000trainers.com/article.
aspx?articleID=56&page=1
Content
5.2 LAN Switches 5.2.2
Access layer switches Access layer switches operate at Layer 2
of the OSI model and provide services such as VLAN membership.
The main purpose of an access layer switch is to allow end
users into the network. An access layer switch should provide
this functionality with low cost and high port density. The
following Cisco switches are commonly used at the access layer:
- Catalyst 1900 series
- Catalyst 2820
series
- Catalyst 2950 series
- Catalyst 4000
series
- Catalyst 5000 series
The Catalyst
1900 or 2820 series switch is an effective access device for
small or medium campus networks. The Catalyst 2950 series
switch effectively provides access for servers and users that
require higher bandwidth. This is achieved by providing Fast
Ethernet capable switch ports. The Catalyst 4000 and 5000
series switches include Gigabit Ethernet ports and are
effective access devices for a larger number of users in large
campus networks. Interactive Media Activity PhotoZoom:
Cisco Catalyst 1912 In this PhotoZoom, the student will view a
Cisco Catalyst 1912. Web Links Cisco Catalyst 2950
Series Switches http://www.cisco.com/en/US/products/
hw/switches/ps628/index.html
Content
5.2 LAN Switches 5.2.3
Distribution layer overview The distribution layer of the
network is between the access and core layers. It helps to
define and separate the core. The purpose of this layer is to
provide a boundary definition in which packet manipulation can
take place. Networks are segmented into broadcast domains by
this layer. Policies can be applied and access control lists
can filter packets. The distribution layer isolates network
problems to the workgroups in which they occur. The
distribution layer also prevents these problems from affecting
the core layer. Switches in this layer operate at Layer 2 and
Layer 3. In a switched network, the distribution layer includes
several functions such as the following: - Aggregation
of the wiring closet connections
- Broadcast/multicast
domain definition
- Virtual LAN (VLAN) routing
- Any media transitions that need to occur
- Security
Web Links Understanding Network
Models – The Cisco Network Design Model
http://www.2000trainers.com/article.
aspx?articleID=56&page=1
Content 5.2 LAN
Switches 5.2.4 Distribution layer switches
Distribution layer switches are the aggregation points for
multiple access layer switches. The switch must be able to
accommodate the total amount of traffic from the access layer
devices. The distribution layer switch must have high
performance. The distribution layer switch is a point at which
a broadcast domain is delineated. The distribution layer
combines VLAN traffic and is a focal point for policy decisions
about traffic flow. For these reasons distribution layer
switches operate at both Layer 2 and Layer 3 of the OSI model.
Switches in this layer are referred to as multilayer switches.
These multilayer switches combine the functions of a router and
a switch in one device. They are designed to switch traffic to
gain higher performance than a standard router. If they do not
have an associated router module, then an external router is
used for the Layer 3 function. The following Cisco switches are
suitable for the distribution layer: - Catalyst 2926G
- Catalyst 5000 family
- Catalyst 6000 family
Interactive Media Activity PhotoZoom: Cisco
Catalyst 2950 In this PhotoZoom, the student will view a Cisco
Catalyst 2950. Web Links Cisco Catalyst 4500 Series
Switches http://www.cisco.com/en/US/products/
hw/switches/ps4324/index.html
Content
5.2 LAN Switches 5.2.5
Core layer overview The core layer is a high-speed switching
backbone. If they do not have an associated router module, an
external router is used for the Layer 3 function. This layer of
the network design should not perform any packet manipulation.
Packet manipulation, such as access list filtering, would slow
down the switching of packets. Providing a core infrastructure
with redundant alternate paths gives stability to the network
in the event of a single device failure. The core can be
designed to use Layer 2 or Layer 3 switching. Asynchronous
Transfer Mode (ATM) or Ethernet switches can be used.
Interactive Media Activity Point and Click: Core Layer
Students completing this activity will be able to identify the
key function of the core layer in the three layer design
model. Web Links Understanding Network Models – The
Cisco Network Design Model http://www.2000trainers.com/
article.aspx?articleID=56&page=1
Content
5.2 LAN Switches 5.2.6
Core layer switches The core layer is the backbone of the
campus switched network. The switches in this layer can make
use of a number of Layer 2 technologies. Provided that the
distance between the core layer switches is not too great, the
switches can use Ethernet technology. Other Layer 2
technologies, such as Asynchronous Transfer Mode (ATM) cell
switching, can also be used. In a network design, the core
layer can be a routed, or Layer 3, core. Core layer switches
are designed to provide efficient Layer 3 functionality when
needed. Factors such as need, cost, and performance should be
considered before a choice is made. The following Cisco
switches are suitable for the core layer: - Catalyst
6500 series
- Catalyst 8500 series
- IGX 8400
series
- Lightstream 1010
Interactive
Media Activity PhotoZoom: Cisco Catalyst 4006 In this
PhotoZoom, the student will view a Cisco Catalyst 4006. Web
Links Cisco Catalyst 6500 Series Switches
http://www.cisco.com/en/US/products/
hw/switches/ps708/index.html
Content Summary An
understanding of the following key points should have been
achieved: - The four major goals of LAN design
- Key considerations in LAN design
- The steps in
systematic LAN design
- Design issues associated with
Layers 1, 2, and 3
- The three-layer design model
- The functions of each layer in the three-layer model
- Cisco access layer switches and their features
- Cisco distribution layer switches and their features
- Cisco core layer switches and their features