Scaling Networks v6.0 Instructor Materials – Chapter 1: LAN Design

Instructor Planning Guide

Activities

What activities are associated with this chapter?

Assessment

Students should complete Chapter 1, “Assessment” after completing Chapter 1.

Quizzes, labs, Packet Tracers and other activities can be used to informally assess student progress.

Sections & Objectives

1.1 Campus Wired LAN Designs

Explain why it is important to design a scalable hierarchical network.

Describe hierarchical small business network designs.

Explain considerations for designing a scalable network.

1.2 Campus Network Device Selection

Select network devices based on feature compatibility and network requirements.

Select the appropriate switch hardware features to support network requirements in small to medium-sized business networks.

Describe the types of routers available for small to medium-sized business networks.

Configure basic settings on a Cisco IOS device.

Chapter 1: LAN Design

1.1 – Campus Wired LAN Designs

1.1.1 – Cisco Validated Designs

1.1.1.1 – The Need to Scale the Network

A company with a small network with one site and a connection to the Internet might grow into an enterprise with a central location with numerous remote sites across the globe.

All enterprise networks must:

  • Support the exchange of various types of network traffic
  • Support critical applications
  • Support converged network traffic
  • Support diverse business needs
  • Provide centralized administrative control

The LAN is the networking infrastructure that provides access to network resources for end users over a single floor or a building.

1.1.1.2 – Hierarchical Design Model

The campus wired LAN uses a hierarchical design model to break the design up into modular layers.

Breaking the design up into layers allows each layer to implement specific functions, which simplifies the network design for easier deployment and management.

A hierarchical LAN design includes three layers as shown in the figure:

  • Access layer
  • Distribution layer
  • Core layer

Some smaller enterprise networks implement a two-tier hierarchical design and collapse the core and distribution layers into one layer.

1.1.2 – Expanding the Network

1.1.2.1 – Design for Scalability

The network designer must develop a strategy to enable the network to be available and scale easily and effectively.

Use expandable, modular equipment or clustered devices that can be easily upgraded to increase capabilities.

Design a hierarchical network to include modules that can be added, upgraded, and modified as needed.

Create an IPv4 or IPv6 address strategy that is hierarchical.

Choose routers or multilayer switches to limit broadcasts and filter undesirable traffic from the network.

Implement redundant links between critical devices and between access and core layers.

1.1.2.2 – Planning for Redundancy

Redundancy is an important part of the network design for preventing disruption of network services.

Minimize the possibility of a single point of failure by recognizing these facts:

  • Installing duplicate equipment and providing failover services for critical devices is necessary.
  • Redundant paths offer alternate physical paths for data to traverse the network.
  • Spanning Tree Protocol (STP) is required with redundant paths in a switched Ethernet network to prevent Layer 2 loops.

STP provides a mechanism for disabling redundant paths in a switched network until the path is necessary such as when a failure occurs.

1.1.2.3 – Failure Domains

A well-designed network should limit the size of failure domains.

A failure domain is the area of a network that is impacted when a critical device or network service experiences problems.

The function of the devices that fail will determine the impact of the failure domain.

Use redundant links and reliable enterprise-class equipment to minimize the disruption in a network.

Smaller failure domains reduce the impact of a failure but also make troubleshooting easier.

In the hierarchical design model, it is usually easier to control the size of a failure domain in the distribution layer.

In the distribution layer, network errors can be contained to a smaller area which will impact fewer users.

When using Layer 3 devices at the distribution layer, every router functions as a gateway for a limited number of access layer users.

Switch Block Deployment

  • Routers or multilayer switches are usually deployed in pairs with access layer switches evenly divided between them.
  • Each switch block acts independently of the others, which reduces the impact of failures.

1.1.2.4 – Increasing Bandwidth

In a hierarchical network design, some links between access and distribution layer switches may need to process a greater amount of traffic than other links do.

As multiple links converge into a single link, it is possible for this link to become a bottleneck.

EtherChannel is a form of link aggregation that will allow the network administrator to increase the amount of bandwidth between devices by creating one logical link out of several physical links.

EtherChannel uses existing switch ports.

The EtherChannel configuration takes advantage of load balancing between links that are part of the same EtherChannel.

1.1.2.5 – Expanding the Access Layer

Wireless connectivity is an important aspect of extending access layer connectivity.

The network must be designed to be able to expand network access to individuals and devices, as needed.

Advantages of wireless connectivity include increased flexibility, reduced cost, and the ability to adapt to changing network and business requirements.

End devices require a wireless NIC that incorporates a radio transmitter/receiver, appropriate software drivers, and also a wireless access point (AP) to connect to.

1.1.2.6 – Fine-tuning Routing Protocols

Advanced routing protocols, such as OSPF and EIGRP are used in large networks.

Link-state routing protocols such as OSPF works well for larger hierarchical networks where fast convergence is important.

Single Area OSPF has one area – Area 0.

Cisco’s proprietary distance vector routing protocol, called EIGRP, is another popular routing protocol. It is designed for larger networks using primarily Cisco routers.

Although the configuring EIGRP is simple, the underlying features and options of EIGRP are extensive and robust.

OSPF supports a two-layer hierarchical design, referred to as multiarea OSPF.

Multiarea OSPF requires an Area 0 (backbone area)

Non-backbone areas must be directly connected to Area 0.

1.2 – Selecting Network Devices

1.2.1 – Switch Hardware

1.2.1.1 – Switch Platforms

Selecting the proper hardware to meet the current network requirements is critical when designing a network.

There are five categories of switches for enterprise networks:

  • Campus LAN switches
  • Cloud-managed switches
  • Data center switches
  • Service provider switches
  • Virtual networking

Various factors to consider when selecting switches include these:

  • Fixed vs. modular configuration
  • Stackable vs. nonstackable
  • Thickness of the switch (rack units)
  • Cost, port density, power, reliability

  • The chassis accepts line cards that contain the ports

1.2.1.2 – Port Density

The port density of a switch refers to the number of ports on a single switch.

Fixed configuration switches support a variety of port density configurations:

  • Cisco Catalyst 3850 24 port and 48 port switches (see figure)
  • The 48 port switch has an option for four additional ports for pluggable SFP devices.

The modular Catalyst 6500 switch shown in the figure can support over 1,000 switch ports.

Modular switches are usually more appropriate in large networks in order to reduce space and power issues.

1.2.1.3 – Forwarding Rates

Entry-level switches have lower forwarding rates than enterprise-level switches.

Forwarding Rates are an important factor when selecting a switch because if the rate is too low, it will not be able to support full wire-speed communication across all of its switch ports.

Access layer switches typically do not need to operate at full wire speed because they are physically limited by their uplinks to the distribution layer.

Higher performing switches are needed at the distribution and core layers.

Switch product lines are classified by forwarding rates.

Forwarding rates define the processing capabilities of a switch by rating how much data the switch can process per second.

1.2.1.4 – Power over Ethernet

PoE allows the switch to deliver power to a device over the existing Ethernet cabling.

This eliminates the need for a power cable to the networked device such an IP phone or wireless access point.

PoE allows more flexibility when installing wireless access points and IP phones by allowing them to be installed anywhere that there is an Ethernet cable.

The Cisco Catalyst 2960-C and 3560-C Series compact switches support PoE pass-through.

PoE pass-through devices can power PoE devices as well as the switch itself by drawing power from certain upstream switches.

1.2.1.5 – Multilayer Switching

Multilayer switches are typically deployed in the core and distribution layer.

Multilayer switches can do the following:

  • Build a routing table and support routing protocols
  • Forward IP packets at a rate close to that of Layer 2 forwarding

Multilayer switches often support specialized hardware called application-specific integrated circuits (ASICs).

ASICs along with dedicated software can streamline the forwarding of IP packets independent of the CPU.

There is a trend in networking toward a pure Layer 3 switched environment.

1.2.1.7 – Packet Tracer – Comparing 2960 and 3560 Switches

This Packet Tracer activity will allow you to use various commands to compare and examine three different switching topologies and compare the 2960 and 3560 switches.

You will also compare the routing table of a 1941 router and a 3560 switch.

1.2.2 – Router Hardware

1.2.2.1 – Router Requirements

Routing is required within the distribution layer of an enterprise network. Without routing, packets could not leave the local network.

Routers are critical networking devices because they are responsible for:

  • Connecting businesses and homes to the Internet
  • Interconnecting multiple sites within an enterprise network
  • Connecting ISPs on the Internet
  • Translating between different media types and protocols
  • Finding alternate paths if a link or path goes down

Routers also serve other important functions:

  • Provide broadcast containment by limiting broadcasts to the local network
  • Group users logically by application or department
  • Provide enhanced security through the use of access control lists in order to filter unwanted traffic.
  • Interconnect geographically separated locations.

1.2.2.2 – Cisco Routers

Selecting the proper router or routers is an important task for the network administrator in order to accommodate a growing network. There are three categories of routers:

  • Branch routers – Branch routers optimize branch services on a single platform while delivering an optimal application experience across branch and WAN infrastructures.
  • Network edge routers – Network edge routers enable the network edge to deliver high-performance, highly secure, and reliable services that unite campus, data center, and branch networks.
  • Service provider routers – Service provider routers differentiate the service portfolio and increase revenues by delivering end-to-end scalable solutions and subscriber-aware services.

1.2.2.3 – Router Hardware

Routers come in many forms:

  • They range in size from a small desktop router to a rack-mounted or blade model router.
  • They can be categorized as fixed configuration or modular.
  • They come with a variety of interfaces such as Fast Ethernet, Gigabit Ethernet, Serial, and fiber-optic.

As an example, the Cisco 1941 router comes with two Gigabit Ethernet RJ-45 interfaces built-in and two slots that can accommodate many different network interface modules.

1.2.3 – Managing Devices

1.2.3.1 – Managing IOS Files and Licensing

When selecting or upgrading a Cisco IOS device, it is important to choose the proper IOS image with the correct feature set and version.

IOS refers to the package of routing, switching, security, and other internetworking technologies integrated into a single multitasking operating system.

When a new device is shipped, it comes preinstalled with the software image and corresponding permanent licenses for the customer-specified packages and features.

For routers beginning with Cisco IOS Software release 15.0, Cisco modified the process to enable new technologies within the IOS feature sets.

1.2.3.2 – In-Band versus Out-of-Band Management

There are two methods for connecting a PC to a network device for configuration and monitoring tasks:

  • Out-of-band management through the use of the console or AUX port is used for the initial configuration or when a network connection is not available.
  • In-band management is used to configure or monitor the device remotely through a network connection using either SSH or HTTPs.
  • A reachable and operational network interface is required.
  • For security reasons, the use of Telnet and HTTP are not recommended.

1.2.3.3 – Basic outer CLI Commands

As shown in the figure to the left, a basic router configuration includes as follows:

  • Hostname for identification
  • Passwords for security
  • Assignment of IP addresses to interfaces for connectivity
  • Basic routing

Verify and save configuration changes with the copy running-config startup-config command

To clear the router configuration, use the erase startup-config and reload commands.

1.2.3.4 – Basic Router Show Commands

The following are some of the most common show commands:

Routing Related:

  • show ip protocols –Displays information about the routing protocols configured
  • show ip route – Displays detailed routing table information including routing codes, known networks, administrative distance and metrics, how routes were learned, next hop, static routes, and default routes

Interface Related:

  • show interfaces – Displays interfaces with line status, bandwidth, delay, reliability, encapsulation, duplex, and I/O statistics

  • show ip interfaces – Displays interface information including protocol status, IPv4 address, if a helper address is configured, and whether an ACL is enabled on the interface
  • show ip interface brief –Displays all interfaces with IPv4 addressing information and interface and line protocol status
  • show protocols – Displays information about the routed protocol that is enabled, and the protocol status of the interfaces

Other connectivity related commands include show cdp neighbors. This command displays information on directly connected Cisco devices including Device ID, the local interface the device is connected to, capability, the platform, and Port ID of the remote device. The details option provides the IP address.

1.2.3.5 – Basic Switch CLI Commands

Basic switch configuration includes these:

  • Hostname for identification
  • Passwords for security
  • Assignment of IP addresses for connectivity. In band-access requires the switch to have an IP address.

See the figure on the left for the commands used to enable and configure the switch.

Use the copy running-config startup-config command to verify and save the switch configuration.

Use the erase startup-config and reload commands to clear the switch configuration.

1.2.3.6 – Basic Switch Show Commands

Switches make use of common IOS commands for configuration, to check for connectivity, and to display current switch status. Here are some very useful commands:

  • show port-security – Displays any ports with security activated. Include the interface ID to examine a specific interface.
  • show port-security address – Displays all secure MAC addresses configured on all switch interfaces.
  • show interfaces – Displays one or all interfaces with line protocol status, bandwidth, delay, reliability, encapsulation, duplex, and I/O statistics.
  • show mac-address-table – Displays all MAC addresses that the switch has learned, how they were learned, port number, and the VLAN assigned to the port.

Cisco switches also support the show cdp neighbors command.

1.3 – Summary

1.3.1 – Summary

1.3.1.3 – Packet Tracer – Skills Integration Challenge

This Packet Tracer activity will require you to practice many of the skills that you have acquired so far during your CCNA studies.

You will first complete the documentation for the network before implementing various requirements.

Finally, you will be required to use your documentation to verify your implementation by testing end-to-end connectivity.

1.3.1.4 – Chapter 1: LAN Design

Explain why it is important to design a scalable hierarchical network.

Select network devices based on feature compatibility and network requirements.

New Terms and Commands

•Mission-critical services

•Enterprise network

•Mission-critical services

•Network operations center (NOC)

•Hierarchical design model

•Access layer

•Distribution layer

•Core layer

•Collapsed core design

•Multilayer switch

•Link aggregation

•Redundancy

•Spanning Tree Protocol (STP)

•Failure domain

•Wireless access point (AP)

•Building switch block

•Departmental switch block

•EtherChannel

•Port channel interface

•Load balancing

•Open Shortest Path First (OSPF)

•Enhanced Interior Gateway Routing Protocol (EIGRP)

•Link-state routing protocol

•Single area OSPF

•Multiarea OSPF

•Distance vector routing protocol

•Form factor

•Power Over Ethernet (PoE)

•Campus LAN switch

•Cloud-managed switch

•Data center switch

•Service provider switch

•Virtual networking switch

•Fixed configuration

•Modular configuration

•Stackable configuration

•Rack unit

•Supervisor engine

•Port density

•Small form-factor pluggable (SFP)

•Forwarding rates

•Wire speed

•Application-specific integrated circuits (ASICs)

•Branch router

•Network edge router

•Service provider router

•Cisco Internetwork Operating System (IOS)

•IOS image

•Out-of-band management

•In-band management

•PuTTY

•TeraTerm

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