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Module 11: Network Design, image, image, image, image - Coggle Diagram
Module 11: Network Design
11.1. Hierarchical Networks
11.1.1 Three-Layer Network Design
Introduces the
three-layer hierarchical model
(Access, Distribution, and Core) as the best practice for designing scalable, high-performance, and manageable networks.
11.1.2 The Need to Scale the Network
Hierarchical design addresses the need to
control complexity
,
improve performance
, and
increase reliability
as a network grows in size (scaling).
It limits broadcast domains and simplifies troubleshooting.
11.1.3 Borderless Switched Networks
The Borderless Network Architecture combines wired and wireless access into a unified structure that extends access securely to anyone, anywhere.
The hierarchical model forms the
underlying structure
that supports this fluid environment.
11.1.4 Hierarchy in the Borderless Switched Network
The hierarchical design provides a
modular approach
, allowing changes to be made in one layer without affecting the entire network.
This modularity is key to managing the continuous evolution of a borderless network.
11.1.5 Access, Distribution, and Core Layer Functions
Access Layer:
Provides network
access
to end-users (switches); manages port security and QoS marking.
Distribution Layer:
Provides
routing
, controls traffic flow via ACLs, and acts as the aggregation point for Access Layer switches.
Core Layer:
Provides
high-speed, backbone switching
to rapidly transport traffic across the network without complex processing.
11.1.6 Three-Tier and Two-Tier Examples
A
Three-Tier model
uses all three layers (Core, Distribution, Access) and is best for
large campus networks
.
A
Two-Tier (Collapsed Core) model
combines the Core and Distribution layers into a single layer, ideal for
smaller campus networks
.
11.1.7 Role of Switched Networks
Switched networks at the Access and Distribution layers provide high-speed, dedicated bandwidth to endpoints and manage traffic aggregation.
The switching functions are foundational to achieving the speed and redundancy required in a modern hierarchical design.
11.2. Scalable Networks
11.2.1 Design for Scalability
Network design must anticipate future growth by using
modular blocks
and a
hierarchical structure
.
Scalability ensures the network can grow in users and traffic volume
without major overhauls
or performance degradation.
11.2.2 Plan for Redundancy
Redundancy
(having duplicate paths or devices) is crucial to minimize downtime and ensure high availability.
Implementing redundant links and devices at the
Distribution and Core layers
prevents single points of failure.
11.2.3 Reduce Failure Domain Size
A
failure domain
is the area of the network impacted when a device or service fails.
Hierarchical design and
VLANs
help limit the size of a failure domain, localizing the impact of an outage.
11.2.4 Increase Bandwidth
Bandwidth can be increased by upgrading to
faster link speeds
(e.g., 10 Gbps) or by using
EtherChannel
to bundle multiple physical links into one logical link.
Increased bandwidth alleviates congestion and supports higher traffic loads.
11.2.5 Expand the Access Layer
The Access Layer is expanded by adding new switches to meet the needs of new users or devices, often organized by
VLANs
for traffic segmentation.
The number of switches and users must remain manageable to prevent large failure domains.
11.2.6 Tune Routing Protocols
Routing protocols (like OSPF or EIGRP) must be
tuned
and configured correctly to ensure
fast convergence
(rapidly adapting to changes) and efficient path selection.
Proper configuration improves network responsiveness and availability.
11.3. Switch Hardware
11.3.1 Switch Platforms
Cisco offers different switch platforms categorized by
function (Access, Distribution, Core)
and
form factor
(fixed, modular, stackable).
Selecting the right platform depends on performance needs, budget, and scalability requirements.
11.3.2 Switch Form Factors
Fixed Configuration Switches
(most common) are limited to the ports they come with and aren't expandable.
Modular Switches
accept different line cards for flexible port types/densities.
Stackable Switches
allow multiple fixed units to operate as a single logical unit.
11.3.3 Port Density
Port density
is the number of ports available on a single switch unit.
It is a key consideration, especially in the
Access Layer
, to connect all end-devices efficiently and manageably.
11.3.4 Forwarding Rates
Forwarding Rate
(or throughput) is the switch's ability to process and forward traffic.
It should be high enough to prevent bottlenecks and is measured by the
number of packets per second (pps)
the switch can handle.
11.3.5 Power over Ethernet (PoE)
PoE
allows a switch to deliver
electrical power
to end devices (like IP phones, wireless access points) over the existing Ethernet cable.
This eliminates the need for separate power outlets, simplifying installation and management.
11.3.6 Multilayer Switching
Multilayer Switches
(Layer 3 switches) can perform both
Layer 2 switching
and
Layer 3 routing
functions.
This capability is essential at the
Distribution Layer
to handle routing between VLANs (inter-VLAN routing) at high speed.
11.3.7 Business Considerations for Switch Selection
Switch selection involves balancing
cost
(CAPEX/OPEX),
port speed/density
,
manageability
(single-unit vs. stack), and
advanced features
(security, PoE, QoS).
11.4. Router Hardware
11.4.1 Router Requirements
Routers are essential for
interconnecting different networks
(LANs, WANs) and for
forwarding packets
based on Layer 3 (IP) addressing.
Requirements include sufficient
port density
,
forwarding rate
, and memory to handle routing tables and high-speed traffic.
11.4.2 Cisco Routers
Cisco provides various router platforms, including
ISR (Integrated Services Routers)
for small-to-midsize branches, and high-performance
Aggregation Services Routers (ASR)
for large enterprises and service providers.
These routers offer modularity for flexible service and connectivity integration.
11.4.3 Router Form Factors
Fixed Configuration Routers
have a set number of non-expandable interfaces, ideal for simple branch or SOHO (Small Office/Home Office) use.
Modular Routers
allow interfaces and service modules to be added or swapped (e.g., WAN cards, voice modules), offering
greater scalability and customization
.
