CCNA 3 v3.1 Module 5
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CCNA 3 Module 5
Switches/LAN Design
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LAN
• Spans a
single room
Building
set of buildings that are close together
• Campus
Group of buildings on a site and belong to a single
organization
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Network Design Requirements
• Functionality of the network
It must work with reasonable speed and reliability
It must allow users to meet their job requirements
• Scalability of the network
Must be able to grow without any major changes to design
• Adaptability of the network
Designed with a vision toward future technologies
• Manageability of the network
It should facilitate network monitoring and management to
ensure ongoing stability of operation
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Why have LANs Expanded
• Development of high-speed technologies
E.g., Asynchronous Transfer Mode (ATM)
• Complex LAN architectures
LAN switching
Virtual LANs (VLANs)
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Design consideration to maximize available
LAN bandwidth and performance
1. The function and placement of servers
2. Collision detection issues
3. Segmentation issues
4. Broadcast domain issues
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LAN Servers
• Provide
File sharing, Printing, Communication, Application services
• Do not function as workstations
• Run specialized operating systems
NetWare, Windows NT, UNIX, and Linux
• Usually dedicated to one function
E.g., e-mail or file sharing
• Categorized into two distinct classes
Enterprise servers
Workgroup servers
• Layer 2 LAN switches located in the MDF and IDFs should
allocated 100 Mbps to these servers
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Enterprise Server
• Supports all the users on the network
service that everyone in an organization would
need (centralized function)
• Offers services such as
e-mail
Domain Name System (DNS)
• Placed in the Main Distribution Facility (MDF)
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Workgroup Server
• Supports a specific set of users
services such as
word processing
file sharing
Print services
• Placed in the Intermediate Distribution
Facilities (IDFs)
Closest to users accessing the applications
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Bridging and Switching
• Excessive collisions reduce available bandwidth by
35% or 40%
• Segmentation with bridges and switches
Splits 1 collision domain into 2 or more collision domains
Create multiple collision domains
Create a single broadcast domain
Stations can get dedicated bandwidth (microsegmentation)
• Broadcast MAC address
FF:FF:FF:FF:FF:FF
Bridges and switches pass broadcast on
Routers filter broadcasts
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LAN Design Methodology
1. Gather requirements and expectations
Identify any current network problems
Information includes
Organization's history
Current status
Projected growth
Operating policies
Management procedures
Office systems and procedures
Viewpoints of the people using the LAN
requirements allow for an informed estimate of costs
and timelines for projected LAN design
implementation
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Availability measures the usefulness of the
network and is affected by
Throughput
Response time
Access to Resources
2.
Analyze requirements and data
User requirements constantly change
Increased need for bandwidth due to
voice and video-based network applications
Assess user requirements
LAN must provide prompt and accurate information
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3. Design the Layer 1, 2, and 3 LAN structure
Star topology or Extended Star topology
Use Ethernet 802.3 CSMA/CD technology
LAN topology design can be broken into
Network layer
Data link layer
Physical layer
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4.
Document the logical and physical network
implementation
Physical topology is the way the various LAN components
are connected together
Logical design is the flow of data in a network and the
naming and addressing schemes used in the
implementation of the LAN design solution.
Specify the locations of the MDF and IDF
Document the type and quantity of cabling
Document spare cables
Useful for troubleshooting
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LAN Design Documents
• OSI layer topology map
• LAN logical map
• LAN physical map
• Cut sheets
• VLAN logical map
• Layer 3 logical map
• Addressing maps
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OSI Layer Topology MAP
Extended Star Topology in a Multi-campus Building
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Cut Sheet
Provide detailed documentation of all cable runs
•Identification numbers
•Port the run is terminated on at the HCC or VCC
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VLAN Logical MAP
Communicates between
VLANs
Group users by department, team or application
Provides broadcast containment and security
Routers provide communication between VLANs
Combines L2 & L3 technology to limit collisions and broadcasts
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Layer 3 Logical MAP
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Addressing Map
Used in troubleshooting
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Layer 1 Design
• Physical Cabling
Fast Ethernet
100 Mbps, can be full-duplex
Fiber-optic backbone
Cat 5e UTP horizontal runs
TIA/EIA-568-A specifications
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TIA/EIA-568-A
•Every device connected to the
network should be linked to a
central location with
horizontal cabling
•Main wiring closet MDF
•IDF needed for every 100 m
•Vertical cable connects
IDF and MDF
(normally fiber cable)
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Layer 2 Design
• Provide flow control, error detection, error
correction, and to reduce congestion in the
network
• Layer 2 devices are bridges and switches
Provide microsegmentation of the network
Reduces the size of collision domains and reduces
collisions
Boost performance for a workgroup or a backbone
• Asymmetric Switching can allocate bandwidth
on a per-port basis (10-Mbps and 100-Mbps
ports )
Provide more bandwidth to vertical cabling, uplinks, and
servers
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Asymmetric Switching
In a pure switched LAN
the size of the collision domain is 2
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All hosts connected to the shared LAN hub
share the same collision domain and bandwidth
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Layer 3 Design
• Router is a layer 3 device
create unique LAN segments
dividing networks into subnetworks, or subnets (scalability)
Allow communication between segments based on Layer 3
addressing (IP addressing)
Forwards data packets based on destination addresses
Does not forward LAN-based broadcasts (e.g., ARP
requests)
Entry and exit point of a broadcast domain
Stops broadcasts from reaching other LAN segments
Serve as firewalls for broadcasts
Allows for segmentation of the LAN into unique physical and
logical networks
Allow for connectivity to wide-area networks (WANs), such as
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Addressing Scheme should be constant throughout the network
Physical port is used to implement VLAN assignment
VLAN 1 - Ports P1, P4, P6
VLAN 2 – Ports P2, P3, P5
Router allows communication
between VLANs
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Hierarchical Design Model
1.
Access layer
Connects end users into the LAN (closest to end user)
Host switches
Workgroup servers
Access layer services provides services such as VLAN membership
2.
Distribution layer
Packet manipulation and Interconnecting workgroups
Layer 3 switches
Enterprise servers
3.
Core layer
Provides the fastest connection between the distribution points – no
packet manipulation
Backbone
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Hierarchical Design Model
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Access Layer
• Entry point for user workstations and servers to
the network
• Access Layer devices are a switch or a hub
Shared bandwidth - Hub
Switched bandwidth - Switch - bandwidth is dedicated
• Access layer functions include
MAC layer filtering - direct frames only to the switch port
that is connected to the destination device
Microsegmentation – 2 devices in collision domain
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Distribution Layer
• Provide boundary definition in which packet manipulation
can take place
• Networks are segmented into broadcast domains
• Policies can be applied
• Access Control Lists can filter packets
• Isolates network problems to workgroups they occur
Prevents these problems affecting the core layer
• Operate at Layer 2 and Layer 3
• Functions
Aggregation of the wiring closet connections
Broadcast/multicast domain definition
Virtual LAN (VLAN) routing
Any media transitions that need to occur
Security
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The Core Layer
• High-speed switching backbone
Interconnects distribution layers
• Router is used for the Layer 3 function
• Should not perform any packet
manipulation
• Use Layer 2 or Layer 3 switching
• Asynchronous Transfer Mode (ATM) or
Ethernet switches can be used
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