© 2014 cisco and bob vachon all rights reserved. 1 chapter 1: introduction to switched networks...

© 2014 Cisco and Bob Vachon All rights reserved. 1

Chapter 1: Introduction to Switched Networks

Switched Networks


Chapter 1 1.1 LAN Design

1.2 The Switched Environment


Chapter 1: Objectives Describe the convergence of data, voice, and video in the

context of switched networks.

Describe a switched network in a small-to-medium-sized business.

Explain the process of frame forwarding in a switched network.

Compare a collision domain to a broadcast domain.


LAN Design


Legacy Telephone Equipment


Separate Networks

Voice Network

Video Network

Data Network


Converged Networks Convergence combines voice and video communications on a

data network.

The impact of moving a conventional company architecture to a completely converged network creates a shared infrastructure resulting in a single network to manage.

A primary benefit of a converged network is that there is just one physical network to install and manage.

• Results in substantial savings over the installation and management of separate voice, video, and data networks.


Converged Networks To support collaboration, business networks employ

converged solutions using voice systems, IP phones, voice gateways, video support, and video conferencing.

https://www.youtube.com/watch?v=DTHHzSKdcaA#t=19


Converged Networks The convergence of services onto the data network has

resulted in an evolution in networks.

It’s gone from a traditional data transport role, to a super-highway for data, voice, and video communication.

Therefore, the converged network must be properly designed and implemented to allow the reliable handling of the various types of information that it must carry.

• A structured design is required to allow management of this complex environment.


Borderless Networks The Cisco Borderless Network provides an architectural

approach that embeds intelligence, simplifies operations, and is scalable to meet demands of the converged network.

It can connect anyone, anywhere, anytime, on any device - securely, reliably, and seamlessly.

It provides the framework to unify wired and wireless access across many different device types.


Borderless Networks Borderless networks are built using following principles:

These are not independent principles, therefore, understanding how each principle fits in the context of the others is critical.

Network Design Principles Explanation

Hierarchy• Facilitates understanding the role of each device at every

tier, simplifies deployment, operation, and management, and reduces fault domains at every tier.

Modularity • Allows seamless network expansion and integrated service enablement on an on-demand basis.

Resiliency • Satisfies user expectations by keeping the network operational.

Flexibility • Allows intelligent traffic load sharing by using all network resources.


Borderless Networks Designing a borderless switched network in a hierarchical

fashion allows network designers to overlay security, mobility, and unified communication features.

There are two time-tested and proven hierarchical design frameworks for campus networks.

Three-tier hierarchical model Two-tier hierarchical model


Borderless Networks Introducing modularity into the campus hierarchical design

further ensures that the campus network remains resilient and flexible enough to provide critical network services.

Modularity also helps to allow for growth and changes that occur over time.


Switched Networks


Role of Switched Networks Switched networks incorporate the following features:

• Layer 3 functionality

• Quality of service

• IP telephony

• Security

• Wireless networking

• Mobility

Meeting the requirements of next generation networks:• Secure

• Reliable and always available

• Support converged network traffic such as data, voice, video, security systems, and more


Switch Considerations There are various types of enterprise switches and the

following are features to consider when selecting them.

Consideration Explanation

Cost • Cost of a switch depends on the number and speed of the interfaces, supported features, and expansion capability.

Port Density • Network switches must support the appropriate number of devices on the network.

Power • Some switches support Power over Ethernet (PoE) . • Some chassis-based switches support redundant power supplies.

Reliability • Switch should provide continuous access to the network.

Port Speed • Speed of the network connection.

Frame Buffers • Switch should be able to store frames for congested ports.

Scalability • Switch should provide the opportunity for growth


Switch Form Factor Switch form factor refers to the type of switch and the

thickness of it when mounted in a rack.

The thickness of the switch is expressed in number of rack units (e.g., 1U, 2U, ….).

Network designers must choose between:• Fixed configuration switch

• Modular configuration switch

• Stackable or non-stackable switch


Fixed Configuration Switches Fixed configuration switches are basically “what you see is

what you get” and they do not support features or options beyond those that originally came with it.

1U


Modular Switches Modular configuration switches are more flexible and typically

come with different sized chassis supporting various modular line cards that fit into the switch chassis.


Stackable Switches These switches can be interconnected using a special cable.

• They can be daisy-chained and effectively managed as one large switch using the Cisco StackWise technology.


L2 and L3 Switches Switches are also identified as either:

• Layer 2

• Layer 3 (or multilayer switch)

L3 switches are typically deployed in the core and distribution layers of an organization's switched network.

• They can build a routing table, support a few routing protocols, and forward IP packets at a rate close to that of Layer 2 forwarding.

• Multilayer switches often support specialized hardware, such as application-specific integrated circuits (ASICs).


L2 and L3 Switches There is a trend in networking toward a pure Layer 3 switched

environment. • Access layer switches are usually L2 switches.

Most switches now support routing and it is likely that soon all switches will incorporate a route processor because the cost of doing so is decreasing relative to other constraints.

• Eventually the term multilayer switch will be redundant.


Enterprise Level Switches Characteristics of enterprise level switches include:

• Port Density

• High Forwarding Rates

• Support for Link Aggregation• Supports higher throughput by combining multiple switch ports


Port Density This is the number of ports available on a single switch.

Remember, some of these ports will be used to interconnect the switch to the rest of the network!


Forwarding Rate Defines the processing capabilities of a switch by rating how

much data the switch can process per second. • Switch product lines are classified by forwarding rates.

• Entry-layer switches have lower forwarding rates than enterprise-layer switches.


Forwarding Rate Wire speed describes the theoretical maximum data

transmission rate that each port on the switch is capable of attaining

• Because access layer switches are physically limited by their uplinks to the distribution layer they don’t need to operate at full wire speed.

Therefore use:• Less expensive, lower performing switches at the access layer

• More expensive, higher performing switches at the distribution and core layers where forwarding rate makes a bigger impact.


Link Aggregation Are there enough ports on a switch to aggregate to support

the required bandwidth?

A 24-port switch, with each port capable of running at gigabit speed could generate up to 24 Gb/s of network traffic.

• What if this switch is connected to the network with one 1 Gbps link?

• Bandwidth contention would occur.

• Each port would get 1/24th of the available wire speed.

• Data would be forwarded more slowly.


Link Aggregation Link aggregation helps reduce traffic bottlenecks by allowing

up to 8 switch ports to be bound together for data communications.

• Link aggregation supports higher throughput by combining multiple switch ports.


Power over Ethernet (PoE) Allows the switch to deliver power to a device over the existing

Ethernet cabling.• Can provide power to IP phones and wireless access points.


PoE Pass-Through Switches Some switches such as the Cisco Catalyst 2960-C and 3560-

C Series compact switches support PoE pass-through.

PoE pass-through allows a network administrator to power PoE devices connected to the switch, as well as the switch itself, by drawing power from certain upstream switches.


Enterprise Switches There is no one switch to “switch them all”.

An enterprise would require the services of many different switches based on its function as a core, distribution, and access layer.

Cisco Switches

http://www.cisco.com/en/US/products/hw/switches/index.html


Access Layer Switches Cisco Catalyst 2960 Series

Cisco Catalyst 2960 and 2960-C Series Compact Switches


Catalyst 2960 Entry-layer enterprise, medium-sized, and branch office

network switch

Forwarding rates from 16 Gb/s to 32 Gb/s

Multilayered switching

QoS features to support IP communications

Access control lists (ACLs)

Fast Ethernet and Gigabit Ethernet connectivity

Up to 48 10/100 ports or 10/100/1000 ports with additional dual purpose gigabit uplinks

No PoE support

CLI, Web management, Network Assistant, console, AUX access


Catalyst 2960


Distribution and Access Layer Switches Cisco Catalyst 3560-X Series

Cisco Catalyst 3750-X Series

Cisco Catalyst 4500E Series


Catalyst 3560 Enterprise-class switch supports PoE, QoS, and advanced

security features (ACLs)

Small enterprise LAN access or branch-office converged network environments.

Different fixed configurations:• Fast Ethernet and Gigabit Ethernet connectivity

• Up to 48 10/100/1000 ports, plus four small form-factor pluggable (SFP) ports

• Optional 10 Gigabit Ethernet connectivity in the Catalyst 3560-E models

• Optional Integrated PoE (Cisco pre-standard and IEEE 802.3af); up to 24 ports with 15.4 watts or 48 ports with 7.3 watts


Catalyst 3560


Catalyst 3750 Access layer switches in midsize organizations and enterprise

branch offices• Forwarding rates from 32 Gb/s to 128 Gb/s

Supports Cisco StackWise technology• StackWise technology allows up to 9 switches to be interconnected via

the use of a fully redundant backplane.

Different stackable fixed configurations:• Fast Ethernet and Gigabit Ethernet connectivity

• Up to 48 10/100/1000 ports, plus four SFP ports

• Optional 10 Gigabit Ethernet connectivity in the Catalyst 3750-E models

• Optional Integrated PoE (Cisco pre-standard and IEEE 802.3af); up to 24 ports with 15.4 watts or 48 ports with 7.3 watts


Catalyst 3750


Catalyst 4500 Distribution Layer switch that provides multilayer switching for

enterprises, small- to medium-sized businesses, and service providers.

• Forwarding rates up to 136 Gb/s

Different modular configurations:• Modular 3, 6, 7, and 10 slot chassis offering different layers of

scalability

• High port density: up to 384 Fast Ethernet or Gigabit Ethernet ports available in copper or fiber with 10 Gigabit uplinks

• PoE (Cisco pre-standard and IEEE 802.3af)

• Dual, hot-swappable internal AC or DC power supplies

• Advanced hardware-assisted IP routing capabilities


Catalyst 4500


Core and Distribution Layer Switches Cisco Catalyst 6500 Series

Cisco Catalyst 4500E Series




Catalyst 6500 Optimized for secure, converged voice, video, and data

networks.

Can manage traffic at the distribution and core layers.

Highest performing Cisco switch• Supports forwarding rates up to 720 Gb/s.

Very large network environments found in enterprises, medium-sized businesses, and service providers.


Core Layer: Catalyst 6500


Catalyst 6500 Different modular configurations:

• Modular 3, 4, 6, 9, and 13 slot chassis

• LAN/WAN service modules

• PoE up to 420 IEEE 802.3af Class 3 (15.4W) PoE devices

• Up to 1152 10/100 ports, 577 10/100/1000 ports, 410 SFP Gigabit Ethernet ports, or 64 10 Gigabit Ethernet ports

• Dual, hot-swappable internal AC or DC power supplies

• Advanced hardware-assisted IP routing capabilities


The Switched Environment


Switching as a General Concept The fundamental concept of switching refers to a device

making a decision based on two criteria:• Ingress port

• Destination address

A LAN switch maintains a MAC Address Table that it uses to determine how to forward traffic through the switch


Dynamically Populating a MAC Address Table As the switch learns the relationship of ports to devices, it

builds a table called a MAC address, or content addressable memory (CAM) table.


Switch Forwarding Methods Application-specific-integrated circuits (ASICs) reduce the

packet-handling time, and allow the device to handle an increased number of ports without degrading performance.

Two Methods of forwarding frames:• Store-and-Forward - makes a forwarding decision on a frame after

it has received the entire frame and checked the frame for errors.

• Cut-Through - begins the forwarding process after the destination MAC address of an incoming frame and the egress port has been determined.

NOTE:• Cisco switches now all use Store and Forward


Selective Forwarding

Cut-ThroughLowest Latency

No error checking

Fragment FreeLow Latency

Checks for collisions

(Filters most errors)

Store-and-ForwardHighest Latency

All errors filtered

Lowest Latency Highest Latency

Less Error Checking More Error Checking


1.2.1.7


Collision Domains Each port on the switch represents a new segment.

Each new segment is a collision domain.


Broadcast Domains Switches do not filter broadcast frames therefore a collection

of interconnected switches forms a single broadcast domain.

Routers are used to segment both collision and broadcast domains


Alleviating Network Congestion Characteristics of switches that contribute to alleviating

network congestion:

Characteristics Explanation

High port density • Large enterprise switches may support many hundreds of ports.

Large frame buffers

• The ability to store many received frames.

Port speed

• Depending on the cost of a switch, it may be possible to support a mixture of speeds.

• Ports of 100 Mb/s, and 1 or 10 Gb/s are common (100 Gb/s is also possible).

Fast internal switching

• Having fast internal forwarding capabilities allows high performance.

Low per-port cost

• Switches provide high-port density at a lower cost and can accommodate network designs featuring fewer users per segment, therefore, increasing the average available bandwidth per user.

© 2014 cisco and bob vachon all rights reserved. 1 chapter 1: introduction to switched networks...

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