be CHAPTER 7 Configuring and Verifying Switch Interfaces This chapter covers the following exam topics: 1.0 Network Fundamentals 111 Explain the role and function of network components LLb 12 and L3 switches 14 Describe switching concepts So far in this part, you have learned the skills to navigate the command-line interface (CLD) and use commands that configure and verify switch features. You learned about the primary purpose of a switch—forwarding Ethernet frames—and learned how to see that process ‘inaction by looking at the switch MAC address table, After learning about che switch data plane in Chapter 5, "Analyzing Ethernet LAN Switching,” you learned a few management plane features in Chapter 6, “Configuring Basic Switch Management,” like how to configure the switch to support Telnet and Secure Shell (SSH) by configuring IP address and login security ‘This chapter focuses on switch interfaces in two major sections. The first section shows how you can configure and change the operation of switch interfaces: how to change the speed, ‘duplex, or even disable the interface, The second half then focuses on how to use show com- sands on a switch to verify switch interface status and how to interpret the output to find some of the more common issues with switch interfaces, “Do I Know This Already?” Quiz ‘Take the quiz (either here or use the PTP software) if you want to use the score to help you decide how mutch time to spend on this chapter. The letter answers are listed at the bottom, of the page following the quiz. Appendix C, found both at the end of the book as well as on the companion website, includes both the answers and explanations. You can also find both answers and explanations in the PTP testing software. ‘Table 7-1 “Do | Know This Already?" Foundation Topics Section-to-Question Mapping irae os Configuring Switch Interfaces 13 Analyzing Switch Interface Status and Statisties [4-6 Technet2aWhich of the following describes a way to disable IEE 10/100 port on a Cisco switch? E standard autonegotiation on a @ Configure the negotiate disable interface subcommand Configure the no negotiate interface subcommand Configure the speed 100 interface subcommand Configure the duplex half interface subcommand Configure the duplex full interface subcommand repo Configure the speed 100 and duplex full interface subcommands In which of the following modes of the CLI could you configure the duplex setting for incerface Fast Ethernet 0/5? a User mode b. Enable mode ‘@. Global configuration mode 4. VLAN mode e. Interface configuration mode A Cisco Catalyst switch connects with its Gigabit0/1 port to an end user's PC. The end user, thinking the user is helping, manually sets the PC’s OS to use a speed of 1000 Mbps and to use full duplex, and disables the use of autonegotiation. The switeh’s GO/L port has default settings for speed and duplex. What speed and duplex settings will the switch decide to use? (Choose two answers.) a. Full duplex b. Half duplex e 10Mbps 4. 1000 Mbps The output of the show interfaces status command on a 2960 switch shows inter face Fa0/l in a “disabled” state, Which of the following is true about interface Fa0/1? joose three answers) a. The interface is configured with the shutdown command b. The show interfaces {40/1 command will lst the interface with two status codes of administratively down and line protocol down, ‘6. The show interfaces fa0/1 command will list the interface with two status codes of up and down. d. The interface cannot currently be used to forward frames, ©. The interface can currently be used to forward frames.182 CCNA 200-801 Official Gert Guide, Volume 1 5. Switch SW/ uses its Gigabit 0/1 interface to connect to switch SW2's Gigabit 0/2 inter- face. SW2s Gi0/2 interface is configured with the speed 1000 and duplex full com- ‘mands. SW/1 uses all defaults for interface configuration commands on its Gi0/1 interface. ‘Which of the following are true about the link after it comes up? (Choose two answers} ‘a The link works at 1000 Mbps (1 Gbps) b. SW! atcempts to run at 10 Mbps because SW? has effectively disabled IEEE stan- dard autonegotiation. ©. The link runs at 1 Gbps, but SW1 uses half duplex and SW?2 uses full duplex. d. Both switches use full duplex. 6. Switch SW1 connects via a cable to switch SW2's GO/I port. Which of the following conditions is the most likely to cause SWS late collision counter to continue to increment? a $W2's GOV has been configured with a shutdown interface subcommand, b. The two switches have been configured with different values on the speed inter- face subcommand, GA duplex mismatch exists with SW1 set to full duplex. dA duplex mismatch exists with SW1 set to half duplex. Configuring Switch Interfaces 10S uses the term interface to refer to physical ports used to forward data to and from other devices. Each interface can be configured with several settings, each of which might differ from interface to interface. TOS uses interface subcommands to configure these settings. Each of these settings may be different from one interface to the next, so you would first identify the specific interface, and thea configure the specific seting, This section begins with a discussion of three relatively basic per-interface settings: the port speed, duplex, and a text description. Following that, the text takes a short look at a pair of the most common interface subcommands: the shutdown and no shutdown commands, ‘which administratively disable and enable the interface, respectively. This section ends with a discussion about autonegotiation concepts, which in turn dictates what settings a switch chooses to use when using autonegotiation Configuring Speed, Duplex, and Description Switch interfaces that support multiple speeds (10/100 and 10/100/1000 interfaces). by default, will autonegotiate what speed to use. However, you can configure the speed and dluplex settings with the duplex (auto I fall half) and speed (auto | 10 | 100 | 1000) inter- face subcommands, Simple enough. Most of the time, using autonegotiation makes good sense, so when you set the duplex and speed manually using these commands, you typically have a good reason to do so. instance, maybe you want to set the speed to the fastest possible on links between switches just to avoid the chance that autonegotiation chooses a slower speed, Technet2arm Chapter 7: Configuring and Verifying Switch interfaces “The description text interface subcommand lets you add a text description to the interface. For instance, if you have good reason to configure the speed and duplex on a port, maybe add a description that says why you did. Example 7-1 shows how to configure duplex and. speed, as well as the description command, which is simply a text description that can be configured by the administrator. Example 7-1 Configuring speed, duplex, and description on Switch Emma ‘ater configuration coapands, one per Line. gad with CxTL/2. kom (contig)# intartace Pasttharnet 0/2 ma (contig-s£1¥ duplex £412 soma (config-s#1# apeed 200 Bona (contig-S£1H description Printer on 24 floor, Preset to 100/ful2 ams (config se1# ante ‘Sona contig) # Anterfuee ange Tastmenernet 0/11 = 20 kom (config-s-rangel# description end-users connect here ‘Boma contigeie-rangel# °z First, focus on the mechanics of moving around in configuration mode again by looking closely at the command prompts. The various interface commands move the user from global mode into interface configuration mode for a specific interface. For instance, the example configures the duplex, speed, and description commands al just after the interface FastEthernet O/1 command, which means that all three of those configuration settings apply to interface Fa0/1, and not to the other interfaces. ‘The show interfaces status command lists much of the detail configured in Example 71, even with only one line of output per interface, Example 7-2 shows an example, just after the configuration in Example 7-1 was added to the switch. Example 7-2 Displaying Interface Status Sestus Vian Duplex speed ype Printer on Sed feo noteannect 1 [EULEYADG 10/00a0erx rpotconnect 2 sto) aus 29/r0cBacens potconnect 2 auro auto 10/100paeeTx connected 3 sefuITae200 20/r008ac0ns potconnect 2 auto auto 10/100baeeTx potconnect 2 auto auto 10/100naveT% hnotconnect 2 auto ute 1/1eapacers potconnect 2 auto auto 10/100na8eT% ras/i0 otconnect 2 auco auto 1/1edpacers Fan/1s —endeusere connect —notconnect 1 auto auto 10/100Haee7x vag/12 end-users connect notonnest 2 auco auto 10/100paserx Fag/13 end-users connect notconnect 2 auto auto 10/100HaGeTx rag/i4—end-unera connect notconnect 1 auco auto 10/100zaserx 183184 CCNA 200-301 Official Gert Guide, Volume 1 30/20 connect Working through the output in the example: FastEthernet 0/1 (Fa0/I): This output lists the first few characters of the configured description. It also lists the configured speed of 100 and duplex full per the speed and duplex commands in Example 7-1. However, it also states that F20/1 has a status of not connect, meaning that the interface is not currently working. (That switch port did not have a cable connected when collecting this example, on purpose.) Fastkithernet 0/2 (Fa0/2}: Example 7-1 did not configute this port at all This port had all default configuration, Note that the “auto” text under the speed and duplex heading means that this port will attempt to autonegotiate both settings when the port comes up. However, this port also does not have a cable connected (again on purpose, for comparison), Ethernet 0/4 (Fa0/4) Like Fa0/2, this port has all default configuration but was cabled to another working device to give yet another contrasting example. This device completed ‘the autonegotiation process, so instead of “auto” under the speed and duplex headings, the output lists the negotiated speed and duplex (a-full and a-100), Note that the text includes the a- to mean that the listed speed and duplex values were autonegotiated, Configuring Multiple Interfaces with the interface range Command The bottom of the configuration in Example 7-1 shows a way to shorten your configuration work when making the same setting on multiple consecutive interfaces. To do so, use the interface range command, In the example, the interface range FastEthernet 0/11 - 20 com- mand tells IOS that the next subcommand(s) apply to interfaces Fa0/11 through Fa0/20. You can define a range as long as all interfaces are the same type and are numbered consecutively. NOTE This book spells out all parameters fully to avoid confusion. However, most every= ‘one abbreviates what they type in the CLI to the shortest unique abbreviation, For instance, the configuration commands int £0/1 and int ran f0/11 - 20 would also be acceptable. 10S does not actually put the interface range command into the configuration, Inte it acts as if you had typed the subcommand under every single interface in the specified ‘Answers to the ‘Do | Know This Already?” quiz: 1F2E3A,D4A,B,.D5A,D6D Technet2aK is Chapter 7: Configuring and Verifying Switch interfaces 1 range. Example 7-3 shows an excerpt from the show running-config command, listing the configuration of interfaces FO/11-12 from the configuration in Example 7-1. The example shows the same description command on both interfaces; to save space, the example does not bother to show all 10 interfaces that have the same description text. Example 7-3 How IOS Expands the Subcommands Typed After interface range interface PaRtethernet0/13 Paststherneto/12 description end-users connect here Administratively Controlling Interface State ‘As you might imagine, network engineers need a way to bring down an interface without having to travel to the switch and remove a cable. In short, we need to be able to decide which ports should be enabled and which should be disabled shutdown In an odd turn of phrase, Cisco uses two interface subcommands to configure the idea of administratively enabling and disabling an interface: the shutdown command (to disable) and the no shutdown command (to enable}. While the no shutdown command might scem like an odd command to enable an interface at fitst, you will use this command a lot in the lab, and it will become second nature. (Most people, in fact, use the abbreviations shut and no shut) Example 7-4 shows an example of disabling an interface using the shutdown interface sub- command. In this case, switch SW has a working interface FO/1. The user connects at the cconsole and disables the interface. IOS generates a log message each time an interface fails or recovers, and log messages appear at the console, as shown in the example, Example 7-4 Administratively Disabling an Interface with shutdown 1 lcontigi# interface tagtzthernet. 0/2 vax 2 02:02:19,702; LIN-5-cHRWG face Fastitherneto/1, SHaRged/SEREGES administratively dow ‘To bring the interface back up again, all you have to do is follow the same process but use the no shutdown command instead, [Before leaving the simple but oddly named shutdown/no shutdown commands, take a look at two important show commands that lst the status of a shutdown interface. The show186 CCNA 200-301 Official Gert Guide, Volume 1 interfaces status command lists one line of output per interface, and winen shut dawn, lists the interface status as “disabled.” That makes logical sense to most people. The show interfaces command (without the status keyword) lsts many lines of output per interface, giving a much more detailed picture of interface status and statistics, With that command, the interface status comes in two parts, with one part using the phrase “administratively down,” matching the highlighted log message in Example 7-4 Example 7-5 shows an example of each of these commands. Note that both examples also use the FO/L parameter (short for Fast Ethernet0/1}, which limits the output to the messages about FO/L only. Also note that FO/l is still shut dowa at this point. Example 7-5 The Different Status Information About Shurdown in Two Different show Commands ‘Siie show interfaces £0/1 atarue rao aisapied x auto auto 10/2008a807% 514 show Antertaces 0/2 Vastuthernet0/2 ia administratively dow, Line protocol is dove (aseableal Hardeare ig Fast Fehernet, adareas 4a 799.947.0082 [bia 1839.547, 0081) MIU 1500 bytes, BW 10000 Hit /ase, DLY 1000 wee, velsability 255/255, txload 1/255, rxtoad 3/255 Encapsulation ARPA, Leap epalive set 110 {input flow-control is off, output flow-control i unsupported ast input never, output 00:00:96, output hang never Input queue: 0/75/0/0 (eize/max/éropa/tlushest ; Total output rope: 9 Queueing strategy: fifo urput queue: 0/40 (aiz0/nax) 5 minute input rate 0 Bite/sec, 0 packets; 5 minate output rate 0 bits/sec, © packsts/soc 264 packata input, 12267 bytes, 0 ao buffer 0 watetdeg, 165 multicast, 0 pause ‘npur 65700 packete output, 5012302 bytes, 0 uderzune ‘output errors, © collisions, 1 sntertace resets Technet2aChapter 7: Configuring and Verifying Switch interfaces 157 Removing Configuration with the no Command ‘One purpose for the specific commands shown in Part Il of the book is to teach you about that command. In some cases, the commands are not the end goal, and the text is attempting to teach you something about how the CLI works, This next short topic is more about the process than about the commands. ‘With some 10S configuration commands (but not all), you can revert to the default set ting by issuing a no version of the command. What does that mean? Let me give you a few examples: 1m If you earlier bad configured speed 100 on an interface, the no speed command on that same interface reverts to the default speed setting (which happens to be speed auto), = Same idea with the duplex command: an earlier configuration of duplex half or duplex full, followed by no duplex on the same interface, reverts the configuration back to the default of duplex auto, = If you had configured a description command with some text, to go back to the default state of having no description command at al for that interface, use the no description ‘command, ple 7-6 shows the process. In this case, switch SW1's FO/2 port has been configured with speed 100, duplex half, description link to 2901-2, and shutdown. You can see evidence of all four settings in the command that begins the example. (This command lists the running-config, but only the part for that one interface.) The example then shows the 7 no versions of those commands and closes with a confirmation that all the commands have reverted to defat Example 7-6 Removing Various Configuration Sertings Using the no Command how wunsingieontig interface £0/2 duplex halt (configit Antertace faatetheraet 0/2 xt (contig-if) # BOEaBER Swi [contig-it)# BeUdeneetpeson