CCNP 642-811 BCMSN Exam Certification Guide - Cisco press

This chapter covers the following topics that you need to master for the CCNP BCMSN exam:

■Ethernet Concepts—This section discusses the concepts and technology behind various forms of Ethernet media. Ethernet solutions for service providers, such as Long Reach Ethernet (LRE) and Metro Ethernet, are also covered.

■Connectivity with Scalable Ethernet—This section covers the configuration steps and commands needed to use Catalyst Ethernet, Fast Ethernet, and Gigabit and 10Gigabit Ethernet switch ports in a network.

■Connecting Switch Block Devices—This section discusses the physical cabling and connectivity used with Catalyst switches, including console and Ethernet interfaces.

■Troubleshooting Port Connectivity—This section covers some of the symptoms, methods, and switch commands that you can use to diagnose problems with Ethernet switch connections.

C H A P T E R 5

Switch Port Configuration

Chapters 1 and 2 dealt with the logical processes that you can use to design a campus network. Connections between switch blocks were discussed, such that traffic could be efficiently transported across the campus. Single connections, load balancing, and redundant paths connected switches in modular blocks for complete connectivity. However, these paths were only functional paths—no specifics were presented about how much traffic the network could handle, or what physical capabilities were supported. These topics become important when you begin to size traffic loads and actually connect Cisco switch devices.

This chapter presents the various Ethernet network technologies used to establish switched connections within the campus network. The chapter also details the switch commands required for configuring and troubleshooting Ethernet LAN ports.

”Do I Know This Already?” Quiz

The purpose of the “Do I Know This Already?” quiz is to help you decide if you need to read the entire chapter. If you already intend to read the entire chapter, you do not necessarily need to answer these questions now.

The 13-question quiz, derived from the major sections in the “Foundation Topics” portion of the chapter, helps you determine how to spend your limited study time.

Table 5-1 outlines the major topics discussed in this chapter and the “Do I Know This Already?” quiz questions that correspond to those topics.

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Table 5-1 “Do I Know This Already?” Foundation Topics Section-to-Question Mapping

CAUTION The goal of self-assessment is to gauge your mastery of the topics in this chapter. If you do not know the answer to a question or are only partially sure of the answer, you should mark this question wrong. Giving yourself credit for an answer you correctly guess skews your selfassessment results and might provide you with a false sense of security.

1.What does the IEEE 802.3 standard define?

a.Spanning Tree Protocol

b.Token Ring

c.Ethernet

d.Switched Ethernet

2.At what layer are traditional 10 Mbps Ethernet, Fast Ethernet, and Gigabit Ethernet the same?

a.Layer 1

b.Layer 2

c.Layer 3

d.Layer 4

3.At what layer are traditional 10 Mbps Ethernet, Fast Ethernet, and Gigabit Ethernet different?

a.Layer 1

b.Layer 2

c.Layer 3

d.Layer 4

”Do I Know This Already?” Quiz 109

4.What is the maximum cable distance for a Category 5 100BASE-TX connection?

a.100 feet

b.100 meters

c.328 meters

d.500 meters

5.Where is Cisco Long Reach Ethernet typically used?

a.In a campus access layer (to the desktop users)

b.In a campus core layer

c.Between campus buildings

d.In a multitenant building

6.What is the maximum length of a Cisco LRE connection?

a.100 feet

b.100 meters

c.500 feet

d.5000 feet

7.Ethernet autonegotiation determines which of the following?

a.Spanning Tree mode

b.Duplex mode

c.Quality of service mode

d.Error threshold

8.Which of the following cannot be determined if the far end of a connection doesn’t support autonegotiation?

a.Link speed

b.Link duplex mode

c.Link media type

d.MAC address

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9.Which of these is not a standard type of Gigabit Interface Converter (GBIC)?

a.1000BASE-LX/LH

b.1000BASE-T

c.1000BASE-FX

d.1000BASE-ZX

10.What type of cable should you use to connect two switches back-to-back using their FastEthernet 10/100 ports?

a.Rollover cable

b.Transfer cable

c.Crossover cable

d.Straight-through cable

11.Assume you have just entered the configure terminal command. To configure the speed of the first FastEthernet interface on a Catalyst 3550 to 100 Mbps, which of these commands should you enter first?

a.speed 100 mbps

b.speed 100

c.interface fastethernet 0/1

d.interface fast ethernet 0/1

12.If a switch port is in the “errdisable” state, what is the first thing you should do?

a.Reload the switch.

b.Use the clear errdisable port command.

c.Use the shut and no shut interface configuration commands.

d.Determine the cause of the problem.

13.Which of the following show interface outputs can you use to diagnose a switch port problem?

a.Port state

b.Port speed

c.Input errors

d.Collisions

e.All of the above

”Do I Know This Already?” Quiz 111

You can find the answers to the quiz in Appendix A, “Answers to Chapter ‘Do I Know This Already?’ Quizzes and Q&A Sections.” The suggested choices for your next step are as follows:

■7 or less overall score—Read the entire chapter. This includes the “Foundation Topics,” “Foundation Summary,” and “Q&A” sections.

■8–10 overall score—Begin with the “Foundation Summary” section and follow up with the “Q&A” section at the end of the chapter.

■11 or more overall score—If you want more review on these topics, skip to the “Foundation Summary” section and then go to the “Q&A” section at the end of the chapter. Otherwise, move to the Chapter 6, “VLANs and Trunks.”

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Foundation Topics

Ethernet Concepts

This section reviews the varieties of Ethernet and their application in a campus network. Recall how the bandwidth requirements for each network segment are determined by the types of applications in use, the traffic flows within the network, and the size of the user community served. Ethernet scales to support increasing bandwidths and should be chosen to match the need at each point in the campus network. As network bandwidth requirements grow, you can scale the links between access, distribution, and core layers to match the load.

Other network media technologies available include Fiber Distribution Data Interface (FDDI), Copper Distribution Data Interface (CDDI), Token Ring, and Asynchronous Transfer Mode (ATM). Although some networks still use these media, Ethernet has emerged as the most popular choice in installed networks. Ethernet is chosen because of its low cost, market availability, and scalability to higher bandwidths.

Ethernet (10 Mbps)

Ethernet is a LAN technology based on the Institute of Electrical and Electronics Engineers (IEEE) 802.3 standard. Ethernet (in contrast to Fast Ethernet and later versions) offers a bandwidth of

10 Mbps between end users. In its most basic form, Ethernet is a shared media that becomes both a collision and a broadcast domain. As the number of users on the shared media increases, so does the probability that a user is trying to transmit data at any given time. Ethernet is based on the carrier sense multiple access collision detect (CSMA/CD) technology, which requires that transmitting stations back off for a random period of time when a collision occurs. The more crowded an Ethernet segment becomes, the less efficient it is.

Ethernet switching addresses this problem by dynamically allocating a dedicated 10-Mbps bandwidth to each of its ports. The resulting increased network performance occurs by reducing the number of users connected to an Ethernet segment.

Although switched Ethernet’s job is to offer fully dedicated bandwidth to each connected device, assuming that network performance will improve across the board when switching is introduced is a common mistake. For example, consider a workgroup of users connected by a shared media Ethernet hub. These users regularly access an enterprise server located elsewhere in the campus network. To improve performance, the decision is made to replace the hub with an Ethernet switch so that all users get dedicated 10-Mbps connections. Because the switch offers dedicated bandwidth for connections between the end user devices connected to its ports, any user-to-user traffic would

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probably see improved performance. However, the enterprise server is still located elsewhere in the network, and all the switched users must still share available bandwidth across the campus to reach it. As discussed in Chapter 1, “Campus Network Overview,” rather than throwing raw bandwidth at a problem, a design based on careful observation of traffic patterns and flows offers a better solution.

Because switched Ethernet can remove the possibility of collisions, stations do not have to listen to each other to take a turn transmitting on the wire. Instead, stations can operate in full-duplex mode—transmitting and receiving simultaneously. Full-duplex mode further increases network performance, with a net throughput of 10 Mbps in each direction, or 20 Mbps total throughput on each port.

Another consideration when dealing with 10-Mbps Ethernet is the physical cabling. Ethernet cabling involves the use of unshielded twisted-pair (UTP) wiring (10BASE-T Ethernet), usually restricted to an end-to-end distance of 100 meters (328 feet) between active devices. Keeping cable lengths as short as possible in the wiring closet also reduces noise and crosstalk when many cables are bundled together.

In a campus network environment, Ethernet is usually used in the access layer, between end user devices and the access layer switch. Many networks still use Ethernet to connect end users to shared media hubs, which then connect to access layer switches. Ethernet is not typically used at either the distribution or core layer.

NOTE Ethernet applications (10BASE2, 10BASE5, 10BASE-F, and so on) use other cabling technologies, though they are not discussed here. For the most part, 10BASE-T with UTP wiring is the most commonly used. A useful website for further reading about Ethernet technology is Charles Spurgeon’s Ethernet Web Site, at www.ethermanage.com/ethernet/.

Long Reach Ethernet (LRE)

In cases where buildings do not have Category 5 UTP wiring, standard 10-Mbps Ethernet might not be possible. Cisco has implemented a different form of Ethernet that can be transported long distances over Category 1, 2, or 3 wiring. This is called Cisco Long Reach Ethernet (LRE).

Cisco LRE is available in the Catalyst 2900 LRE XL Switch Series. Multiple LRE ports are used to connect into existing building wiring (often used for telephone connections) to provide Ethernet capability to a building’s tenants. LRE can provide 5 Mbps full-duplex bandwidth over connections up to 5000 feet, 10 Mbps up to 4000 feet, or 15 Mbps up to 3000 feet. LRE can co-exist on the same physical building wiring pairs with POTS and ISDN, and in the same building (different wiring pairs) with Asymmetric Digital Subscriber Line (ADSL).

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Fast Ethernet operates at 100 Mbps and is defined in the IEEE 802.3u standard. The Ethernet cabling schemes, CSMA/CD operation, and all upper-layer protocol operations are maintained with Fast Ethernet. The net result is the same data link Media Access Control (MAC) layer merged with a new physical layer.

The campus network can use Fast Ethernet to link access and distribution layer switches, if no higher-speed links are available. These links can support the aggregate traffic from multiple Ethernet segments in the access layer. Fast Ethernet is generally used to connect end user workstations to the access layer switch and to provide improved connectivity to enterprise servers.

Cabling for Fast Ethernet can involve either UTP or fiber. Table 5-2 lists the specifications for Fast Ethernet that define the media types and distances.

Table 5-2 Cabling Specifications for Fast Ethernet

Full-Duplex Fast Ethernet

As with traditional Ethernet, the natural progression to improve performance is to use full-duplex operation. Fast Ethernet can provide 100 Mbps in each direction on a switched connection, for 200 Mbps total throughput. This throughput is possible only when a workstation, server, or a router directly connects to a switch port, or when two switches directly connect to each other. In any case, the operating system or firmware on each end of the connection must support full-duplex operation.

The Fast Ethernet specification also offers backward-compatibility to support traditional 10-Mbps Ethernet. In the case of 100BASE-TX, switch ports are often called “10/100” ports, to denote the dual speed. To provide this support, the two devices at each end of a network connection can automatically negotiate link capabilities so that they can both operate at a maximum common level. This negotiation involves detecting and selecting the highest physical layer technology (available bandwidth) and half-duplex or full-duplex operation. To properly negotiate a connection, both ends should be configured for autonegotiation.