Chapter 7

Managing a Cisco Internetwork

The following ICND1 exam topics are covered in this chapter:

• LAN Switching Technologies

• Verify network status and switch operation using basic utilities such as ping, telnet, and ssh

• IP Routing Technologies

• Configure and verify utilizing the CLI to set basic Router configuration
• Cisco IOS commands to perform basic router setup
• Verify router configuration and network connectivity
• Cisco IOS commands to review basic router information and network connectivity

• IP Services

• Configure and verify DHCP (IOS Router)
• configuring router interfaces to use DHCP
• DHCP options
• excluded addresses
• lease time
• Configure and verify NTP as a client

Here in Chapter 7, I’m going to show you how to manage Cisco routers and switches on an internetwork. You’ll find out how to manage Cisco devices by using the copy command with a TFTP host and how to configure DHCP and NTP, plus you’ll get a survey of the Cisco Discovery Protocol (CDP). I’ll also show you how to resolve hostnames.

I’ll wrap up the chapter by guiding you through some important Cisco IOS troubleshooting techniques to ensure that you’re well equipped with these key skills.

To find up-to-the minute updates for this chapter, please see www.lammle.com/forum or the book’s web page at www.sybex.com.

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The Internal Components of a Cisco Router and Switch

Unless you happen to be really savvy about the inner and outer workings of all your car’s systems and its machinery and how all of that technology works together, you’ll take it to someone who does know how to keep it maintained, figure out what’s wrong when it stops running, and get it up and running again. It’s the same deal with Cisco networking devices—you need to know all about their major components, pieces, and parts as well as what they all do and why and how they all work together to make a network work. The more solid your knowledge, the more expert you are about these things and the better equipped you’ll be to configure and troubleshoot a Cisco internetwork. Toward that goal, study Table 7-1 for an introductory description of a Cisco router’s major components.

Table 7-1: Cisco router components

The Router and Switch Boot Sequence

When a Cisco device boots up, it performs a series of steps, called the boot sequence, to test the hardware and load the necessary software. The boot sequence comprises the following steps:

The default order of an IOS loading from a Cisco device begins with flash, then TFTP server, and finally, ROM.

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Backing Up and Restoring the Cisco Configuration

Any changes that you make to the configuration are stored in the running-config file. And if you don’t enter a copy run start command after you make a change to running-config, that change will totally disappear if the device reboots or gets powered down. As always, backups are good, so you’ll want to make another backup of the configuration information just in case the router or switch completely dies on you. Even if your machine is healthy and happy, it’s good to have a backup for reference and documentation reasons!

Next, I’ll cover how to copy the configuration of a router to a TFTP server as well as how to restore that configuration.

Backing Up the Cisco Configuration

To copy the configuration from an IOS device to a TFTP server, you can use either the copy running-config tftp or the copy startup-config tftp command. Either one will back up the router configuration that’s currently running in DRAM or one that’s stored in NVRAM.

Verifying the Current Configuration

To verify the configuration in DRAM, use the show running-config command (sh run for short) like this:

Router#show running-config
Building configuration...

Current configuration : 855 bytes
!
version 15.0

The current configuration information indicates that the router is running version 15.0 of the IOS.

Verifying the Stored Configuration

Next, you should check the configuration stored in NVRAM. To see this, use the show startup-config command (sh start for short) like this:

Router#sh start
Using 855 out of 524288 bytes
!
! Last configuration change at 04:49:14 UTC Fri Mar 5 1993
!
version 15.0

The first line shows you how much room your backup configuration is taking up. Here, we can see that NVRAM is about 524 KB and that only 855 bytes of it are being used. But memory is easier to reveal via the show version command when you’re using an ISR router.

If you’re not sure that the files are the same and the running-config file is what you want to go with, then use the copy running-config startup-config command. This will help you ensure that both files are in fact the same. I’ll guide you through this in the next section.

Copying the Current Configuration to NVRAM

By copying running-config to NVRAM as a backup, as shown in the following output, you ensure that your running-config will always be reloaded if the router gets rebooted. Starting in the 12.0 IOS, you’ll be prompted for the filename you want to use:

Router#copy running-config startup-config
Destination filename [startup-config]?[enter]
Building configuration...
[OK]

The reason the filename prompt appears is that there are now so many options you can use when using the copy command—check it out:

Router#copy running-config ?
  flash:          Copy to flash: file system
  ftp:            Copy to ftp: file system
  http:           Copy to http: file system
  https:          Copy to https: file system
  null:           Copy to null: file system
  nvram:          Copy to nvram: file system
  rcp:            Copy to rcp: file system
  running-config  Update (merge with) current system configuration
  scp:            Copy to scp: file system
  startup-config  Copy to startup configuration
  syslog:         Copy to syslog: file system
  system:         Copy to system: file system
  tftp:           Copy to tftp: file system
  tmpsys:         Copy to tmpsys: file system

We’ll go over the copy command in more detail in the Sybex ICND2 Study Guide.

Copying the Configuration to a TFTP Server

Once the file is copied to NVRAM, you can make a second backup to a TFTP server by using the copy running-config tftp command, or copy run tftp for short. I’m going to set the hostname to Todd before I run this command:

Todd#copy running-config tftp

Address or name of remote host []? 10.10.10.254
Destination filename [todd-confg]?
!!
776 bytes copied in 0.800 secs (970 bytes/sec)

If you have a hostname already configured, the command will automatically use the hostname plus the extension -confg as the name of the file.

Restoring the Cisco Configuration

What do you do if you’ve changed your running-config file and want to restore the configuration to the version in the startup-config file? The easiest way to get this done is to use the copy startup-config running-config command, or copy start run for short, but this will work only if you copied running-config into NVRAM before you made any changes! Of course, a reload of the device will work too!

If you did copy the configuration to a TFTP server as a second backup, you can restore the configuration using the copy tftp running-config command (copy tftp run for short), or the copy tftp startup-config command (copy tftp start for short), as shown in the output below. Just so you know, the old command we used to use for this is config net:

Todd#copy tftp running-config
Address or name of remote host []?10.10.10.254
Source filename []?todd-confg
Destination filename[running-config]?[enter]
Accessing tftp://10.10.10.254/todd-confg...
Loading todd-confg from 10.10.10.254 (via FastEthernet0/0):
!!
[OK - 776 bytes]
776 bytes copied in 9.212 secs (84 bytes/sec)
Todd#
*Mar  7 17:53:34.071: %SYS-5-CONFIG_I: Configured from
    tftp://10.10.10.254/todd-confg by console

Okay, here we can see that the configuration file is an ASCII text file, meaning that before you copy the configuration stored on a TFTP server back to a router, you can make changes to the file with any text editor.

Remember that when you copy or merge a configuration from a TFTP server to a freshly erased and rebooted router’s RAM, the interfaces are shut down by default and you must manually enable each interface with the no shutdown command.

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Erasing the Configuration

To delete the startup-config file on a Cisco router or switch, use the command erase startup-config, like this:

Todd#erase startup-config
Erasing the nvram filesystem will remove all configuration files!
    Continue? [confirm][enter]
[OK]
Erase of nvram: complete
*Mar  7 17:56:20.407: %SYS-7-NV_BLOCK_INIT: Initialized the geometry of nvram
Todd#reload
System configuration has been modified. Save? [yes/no]:n
Proceed with reload? [confirm][enter]
 *Mar  7 17:56:31.059: %SYS-5-RELOAD: Reload requested by console.
    Reload Reason: Reload Command.

This command deletes the contents of NVRAM on the switch and router. If you type reload while in privileged mode and say no to saving changes, the switch or router will reload and come up into setup mode.

Configuring DHCP

We went over DHCP in Chapter 3, “Introduction to TCP/IP”, where I described how it works and what happens when there’s a conflict. At this point, you’re ready to learn how to configure DHCP on Cisco’s IOS as well as how to configure a DHCP forwarder for when your hosts don’t live on the same LAN as the DHCP server. Do you remember the four-way handshake hosts used to get an address from a server? If not, now would be a really great time to head back to Chapter 3 and thoroughly review that before moving on with this!

To configure a DHCP server for your hosts, you need the following information at minimum:

Here are your configuration steps:

I’ll configure the switch in Figure 7-1 to be the DHCP server for the Sales Wireless LAN.

Figure 7-1: DHCP Configuration example on a switch

Understand that this configuration could just have easily been placed on the router in Figure 7-1. Here’s how we’ll configure DHCP using the 192.168.10.0/24 network ID:

Switch(config)#ip dhcp excluded-address 192.168.10.1 192.168.10.10
Switch(config)#ip dhcp pool Sales_Wireless
Switch(dhcp-config)#network 192.168.10.0 255.255.255.0
Switch(dhcp-config)#default-router 192.168.10.1
Switch(dhcp-config)#dns-server 4.4.4.4
Switch(dhcp-config)#lease 3 12 15

First, you can see that I reserved 10 addresses in the range for the router, servers, and printers, etc. I then created the pool named Sales_Wireless, added the default gateway and DNS server, and set the lease to 3 days, 12 hours, and 15 minutes (which isn’t really significant because I just set it that way for demonstration purposes). Pretty straightforward, right? The switch will now respond to DHCP client requests. But what happens if we need to provide an IP address from a DHCP server to a host that’s not in our broadcast domain, or if we want to receive a DHCP address for a client from a remote server?

DHCP Relay

If you need to provide addresses from a DHCP server to hosts that aren’t on the same LAN as the DHCP server, you can configure your router interface to relay or forward the DHCP client requests, as shown in Figure 7-2. If we don’t provide this service, our router would receive the DHCP client broadcast, promptly discard it, and the remote host would never receive an address—unless we added a DHCP server on every broadcast domain! Let’s take a look at how we would typically configure DHCP service in today’s networks.

So we know that because the hosts off the router don’t have access to a DHCP server, the router will simply drop their client request broadcast messages by default. To solve this problem, we can configure the F0/0 interface of the router to accept the DHCP client requests and forward them to the DHCP server like this:

Router#config t
Router(config)#interface fa0/0
Router(config-if)#ip helper-address 10.10.10.254

Figure 7-2: Configuring a DHCP relay

Now I know that was a pretty simple example, and there are definitely other ways to configure the relay, but rest assured that I’ve covered the objectives for you. Also, I want you to know that ip helper-address forwards more than just DHCP client requests, so be sure to research this command before you implement it! Now that I’ve demonstrated how to create the DHCP service, let’s take a minute to verify DHCP before moving on to NTP.

Verifying DHCP on Cisco IOS

There are some really useful verification commands to use on a Cisco IOS device for monitoring and verifying a DHCP service. You’ll get to see the output for these commands when I build the network in Chapter 8, “IP Routing,” and add DHCP to the two remote LANs. I just want you to begin getting familiar with them, so here’s a list of four very important ones and what they do:

Again, no worries because we’ll cover these vital commands thoroughly in the next chapter.

Network Time Protocol (NTP)

Network Time Protocol provides pretty much what it describes: time to all your network devices. To be more precise, NTP synchronizes clocks of computer systems over packet-switched, variable-latency data networks.

Typically you’ll have an NTP server that connects through the Internet to an atomic clock. This time can then be synchronized through the network to keep all routers, switches, servers, etc. receiving the same time information.

Correct network time within the network is important:

• Correct time allows the tracking of events in the network in the correct order.
• Clock synchronization is critical for the correct interpretation of events within the syslog data.
• Clock synchronization is critical for digital certificates.

Making sure all your devices have the correct time is especially helpful for your routers and switches for looking at logs regarding security issues or other maintenance issues. Routers and switches issue log messages when different events take place—for example, when an interface goes down and then back up. As you already know, all messages generated by the IOS go only to the console port by default. However, as shown in Figure 7-3, those console messages can be directed to a syslog server.

Figure 7-3: Sending console messages to a syslog server

A syslog server saves copies of console messages and can time-stamp them so you can view them at a later time. This is actually rather easy to do. Here would be your configuration on the SF router:

SF(config)#logging host 172.16.10.1
SF(config)#service timestamps log datetime msec

Now all the console messages will be stored in one location that you can view at your convenience. However, even though I had the messages time-stamped in Figure 7-3 with the command service timestamps log datetime msec, this doesn’t mean that we’ll know the exact time if using default clock sources. To make sure all devices are synchronized with the same time information, we’ll configure our devices to receive the accurate time information from a centralized server, as shown in Figure 7-4:

SF(config)#ntp server 172.16.10.1 version 4

Figure 7-4: Synchronizing time information

Just use that one simple command on all your devices and each network device on your network will then have the same exact time and date information. You can then rest assured that your time stamps are accurate. You can also make your router or switch be an NTP server with the ntp master command.

To verify our VTP client is receiving clocking information, we use the following commands:

SF#sh ntp ?
  associations  NTP associations
  status        NTP status  status     VTP domain status

SF#sh ntp status
Clock is unsynchronized, stratum 16, no reference clock
nominal freq is 119.2092 Hz, actual freq is 119.2092 Hz, precision is 2**18
reference time is 00000000.00000000 (00:00:00.000 UTC Mon Jan 1 1900)
clock offset is 0.0000 msec, root delay is 0.00 msec

S1#sh ntp associations 

address    ref clock     st  when  poll reach  delay  offset    disp
 ~172.16.10.1   0.0.0.0          16     -    64    0     0.0    0.00  16000.
 * master (synced), # master (unsynced), + selected, - candidate, ~ configured

You can see in the example that the NTP client in SF is not synchronized with the server by using the show ntp status command. The stratum value is a number from 1 to 15, and a lower stratum value indicates a higher NTP priority; 16 means there is no clocking received.

There are many other configurations of an NTP client that are available, such as authentication of NTP so a router or switch isn’t fooled into changing the time of an attack, for example.

Using Cisco Discovery Protocol (CDP)

Cisco Discovery Protocol (CDP) is a proprietary protocol designed by Cisco to help administrators collect information about locally attached devices. Armed with CDP, you can gather hardware and protocol information about neighbor devices, which is crucial information to have when troubleshooting and documenting the network.

Let’s start by exploring the CDP timer and CDP commands we’ll need to verify our network.

Getting CDP Timers and Holdtime Information

The show cdp command (sh cdp for short) gives you information about two CDP global parameters that can be configured on Cisco devices:

• CDP timer delimits how often CDP packets are transmitted out all active interfaces.
• CDP holdtime delimits the amount of time that the device will hold packets received from neighbor devices.

Both Cisco routers and switches use the same parameters. Check out Figure 7-5 to see how CDP works within a switched network that I set up for my switching labs in this book.

Figure 7-5: Cisco Discovery Protocol

The output on my 3560 SW-3 looks like this:

SW-3#sh cdp
Global CDP information:
        Sending CDP packets every 60 seconds
        Sending a holdtime value of 180 seconds
        Sending CDPv2 advertisements is enabled

This output tells us that the default transmits every 60 seconds and will hold packets from a neighbor in the CDP table for 180 seconds. I can use the global commands cdp holdtime and cdp timer to configure the CDP holdtime and timer on a router if necessary like this:

SW-3(config)#cdp ?
  advertise-v2  CDP sends version-2 advertisements
  holdtime      Specify the holdtime (in sec) to be sent in packets
  run           Enable CDP
  timer         Specify the rate at which CDP packets are sent (in sec)
  tlv           Enable exchange of specific tlv information

SW-3(config)#cdp holdtime ?
  <10-255>  Length  of time  (in sec) that receiver must keep this packet

SW-3(config)#cdp timer ?
  <5-254>  Rate at which CDP packets are sent (in  sec)

You can turn off CDP completely with the nocdprun command from global configuration mode of a router and enable it with the cdp run command:

SW-3(config)#no cdp run
SW-3(config)#cdp run

To turn CDP off or on for an interface, use the no cdp enable and cdp enable commands.

Gathering Neighbor Information

The show cdp neighbor command (sh cdp nei for short) delivers information about directly connected devices. It’s important to remember that CDP packets aren’t passed through a Cisco switch and that you only see what’s directly attached. So this means that if your router is connected to a switch, you won’t see any of the Cisco devices connected to that switch!

The following output shows the show cdp neighbor command I used on my SW-3:

SW-3#sh cdp neighbors
Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge
                  S - Switch, H - Host, I - IGMP, r - Repeater, P - Phone,
                  D - Remote, C - CVTA, M - Two-port Mac Relay Device ID     Local Intrfce     Holdtme    Capability  Platform  Port ID
SW-1   Fas 0/1      170          S I     WS-C3560- Fas 0/15
SW-1   Fas 0/2      170          S I     WS-C3560- Fas 0/16
SW-2   Fas 0/5      162          S I     WS-C3560- Fas 0/5
SW-2   Fas 0/6      162          S I     WS-C3560- Fas 0/6

Okay—we can see that I’m directly connected with a console cable to the SW-3 switch and also that SW-3 is directly connected to two other switches. However, do we really need the figure to draw out our network? We don’t! CDP allows me to see who my directly connected neighbors are and gather information about them. From the SW-3 switch, we can see that there are two connections to SW-1 and two connections to SW-2. SW-3 connects to SW-1 with ports Fas 0/1 and Fas 0/2, and we have connections to SW-2 with local interfaces Fas 0/5 and Fas 0/6. Both the SW-1 and SW-2 switches are 3650 switches, and SW-1 is using ports Fas 0/15 and Fas 0/16 to connect to SW-3. SW-2 is using ports Fas 0/5 and Fas 0/6.

To sum this up, the device ID shows the configured hostname of the connected device, that the local interface is our interface, and the port ID is the remote devices’ directly connected interface. Remember that all you get to view are directly connected devices!

Table 7-2 summarizes the information displayed by the show cdp neighbor command for each device.

Table 7-2: Output of the show cdp neighbors command

It’s imperative that you can look at the output of a show cdp neighbors command and decipher the information gained about the neighbor device’s capability, whether it’s a router or switch, the model number (platform), your port connecting to that device (local interface), and the port of the neighbor connecting to you (port ID).

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Another command that will deliver the goods on neighbor information is the show cdp neighbors detail command (show cdp nei de for short). This command can be run on both routers and switches, and it displays detailed information about each device connected to the device you’re running the command on. Check out the router output in Listing 7-1.

Listing 7-1: Showing CDP Neighbors

SW-3#sh cdp neighbors detail
-------------------------
Device ID: SW-1
Entry address(es):
  IP address: 10.100.128.10
Platform: cisco WS-C3560-24TS,  Capabilities: Switch IGMP
Interface: FastEthernet0/1,  Port ID (outgoing port): FastEthernet0/15
Holdtime : 137 sec

Version :
Cisco IOS Software, C3560 Software (C3560-IPSERVICESK9-M), Version 12.2(55)SE7, RELEASE SOFTWARE (fc1)
Technical Support: http://www.cisco.com/techsupport
Copyright (c) 1986-2013 by Cisco Systems, Inc.
Compiled Mon 28-Jan-13 10:10 by prod_rel_team

advertisement version: 2
Protocol Hello:  OUI=0x00000C, Protocol ID=0x0112; payload len=27, value=00000000FFFFFFFF010221FF000000000000001C575EC880FF0000
VTP Management Domain: 'NULL'
Native VLAN: 1
Duplex: full
Power Available TLV:

    Power request id: 0, Power management id: 1, Power available: 0, Power management level: -1
Management address(es):
  IP address: 10.100.128.10
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[ouput cut]

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Device ID: SW-2
Entry address(es):
  IP address: 10.100.128.9
Platform: cisco WS-C3560-8PC,  Capabilities: Switch IGMP
Interface: FastEthernet0/5,  Port ID (outgoing port): FastEthernet0/5
Holdtime : 129 sec

Version :
Cisco IOS Software, C3560 Software (C3560-IPBASE-M), Version 12.2(35)SE5, RELEASE SOFTWARE (fc1)
Copyright (c) 1986-2007 by Cisco Systems, Inc.
Compiled Thu 19-Jul-07 18:15 by nachen

advertisement version: 2
Protocol Hello:  OUI=0x00000C, Protocol ID=0x0112; payload len=27, value=00000000FFFFFFFF010221FF000000000000B41489D91880FF0000
VTP Management Domain: 'NULL'
Native VLAN: 1
Duplex: full
Power Available TLV:

    Power request id: 0, Power management id: 1, Power available: 0, Power management level: -1
Management address(es):
  IP address: 10.100.128.9
[output cut]

So what’s revealed here? First, we’ve been given the hostname and IP address of all directly connected devices. And in addition to the same information displayed by the show cdp neighbor command (see Table 7-2), the show cdp neighbor detail command tells us about the IOS version and IP address of the neighbor device—that’s quite a bit!

The show cdp entry * command displays the same information as the show cdp neighbors detail command. There isn’t any difference between these commands.

CDP Can Save Lives!

Karen has just been hired as a senior network consultant at a large hospital in Dallas, Texas, so she’s expected to be able to take care of any problem that rears its ugly head. As if that weren’t enough pressure, she also has to worry about the horrid possibility that people won’t receive correct health care solutions—even the correct medications—if the network goes down. Talk about a potential life-or-death situation!

But Karen is confident and begins her job optimistically. Of course, it’s not long before the network reveals that it has a few problems. Unfazed, she asks one of the junior administrators for a network map so she can troubleshoot the network. This person tells her that the old senior administrator, who she replaced, had them with him and now no one can find them. The sky begins to darken!

Doctors are calling every couple of minutes because they can’t get the necessary information they need to take care of their patients. What should she do?

It’s CDP to the rescue! And it’s a gift that this hospital happens to be running Cisco routers and switches exclusively, because CDP is enabled by default on all Cisco devices. Karen is also in luck because the disgruntled former administrator didn’t turn off CDP on any devices before he left!

So all Karen has to do now is to use the show cdp neighbor detail command to find all the information she needs about each device to help draw out the hospital network, bringing it back up to speed so the personnel who rely upon it can get on to the important business of saving lives!

The only snag for you nailing this in your own network is if you don’t know the passwords of all those devices. Your only hope then is to somehow find out the access passwords or to perform password recovery on them.

So, use CDP—you never know when you may end up saving someone’s life.

By the way, this is a true story!

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Documenting a Network Topology Using CDP

With that moving real-life scenario in mind, I’m now going to show you how to document a sample network by using CDP. You’ll learn to determine the appropriate router types, interface types, and IP addresses of various interfaces using only CDP commands and the show running-config command. And you can only console into the Lab_A router to document the network. You’ll have to assign any remote routers the next IP address in each range. We’ll use a different figure for this example—Figure 7-6— to help us to complete the necessary documentation.

Figure 7-6: Documenting a network topology using CDP

In this output, you can see that you have a router with four interfaces: two Fast Ethernet and two serial. First, determine the IP addresses of each interface by using the show running-config command like this:

Lab_A#sh running-config
Building configuration...

Current configuration : 960 bytes
!
version 12.2
service timestamps debug uptime
service timestamps log uptime
no service password-encryption
!
hostname Lab_A
!
ip subnet-zero
!
!
interface FastEthernet0/0
 ip address 192.168.21.1 255.255.255.0
 duplex auto
!
interface FastEthernet0/1
 ip address 192.168.18.1 255.255.255.0
 duplex auto
!
interface Serial0/0
ip address 192.168.23.1 255.255.255.0
!
interface Serial0/1
ip address 192.168.28.1 255.255.255.0
!
ip classless
!
line con 0
line aux 0
line vty 0 4
!
end

With this step completed, you can now write down the IP addresses of the Lab_A router’s four interfaces. Next, you must determine the type of device on the other end of each of these interfaces. It’s easy—just use the show cdp neighbors command:

Lab_A#sh cdp neighbors
Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge
S - Switch, H - Host, I - IGMP, r - Repeater
Device ID   Local Intrfce     Holdtme    Capability Platform  Port ID
Lab_B        Fas 0/0            178          R        2501     E0
Lab_C        Fas 0/1            137          R        2621     Fa0/0
Lab_D        Ser 0/0            178          R        2514     S1
Lab_E        Ser 0/1            137          R        2620     S0/1

Wow—looks like we’re connected to some old routers! But it’s not our job to judge. Our mission is to draw out our network, so it’s good that we’ve got some nice information to meet the challenge with now. By using both the show running-config and show cdp neighbors commands, we know about all the IP addresses of the Lab_A router, the types of routers connected to each of the Lab_A router’s links, and all the interfaces of the remote routers.

Now that we’re equipped with all the information gathered via show running-config and show cdp neighbors, we can accurately create the topology in Figure 7-7.

If we needed to, we could’ve also used the show cdp neighbors detail command to view the neighbor’s IP addresses. But since we know the IP addresses of each link on the Lab_A router, we already know what the next available IP address is going to be.

Figure 7-7: Network topology documented

Link Layer Discovery Protocol (LLDP)

Before moving on from CDP, I want to tell you about a nonproprietary discovery protocol that provides pretty much the same information as CDP but works in multi-vendor networks.

The IEEE created a new standardized discovery protocol called 802.1AB for Station and Media Access Control Connectivity Discovery. We’ll just call it Link Layer Discovery Protocol (LLDP).

LLDP defines basic discovery capabilities, but it was also enhanced to specifically address the voice application, and this version is called LLDP-MED (Media Endpoint Discovery). It’s good to remember that LLDP and LLDP-MED are not compatible.

You can find out more about these protocols at these two locations:

www.cisco.com/en/US/docs/ios/cether/configuration/guide/ce_lldp-med.html

www.cisco.com/en/US/technologies/tk652/tk701/technologies_white_paper0900aecd804cd46d.html

But it’s probably easier to go to www.cisco.com and search on LLDP than type in the URLs above.

Using Telnet

As part of the TCP/IP protocol suite, Telnet is a virtual terminal protocol that allows you to make connections to remote devices, gather information, and run programs.

After your routers and switches are configured, you can use the Telnet program to reconfigure and/or check up on them without using a console cable. You run the Telnet program by typing telnet from any command prompt (Windows or Cisco), but you need to have VTY passwords set on the IOS devices for this to work.

Remember, you can’t use CDP to gather information about routers and switches that aren’t directly connected to your device. But you can use the Telnet application to connect to your neighbor devices and then run CDP on those remote devices to get information on them.

You can issue the telnet command from any router or switch prompt. Below, I’m trying to telnet from switch 1 to switch 3:

SW-1#telnet 10.100.128.8
Trying 10.100.128.8 ... Open

Password required, but none set

[Connection to 10.100.128.8 closed by foreign host]

Oops—clearly, I didn’t set my passwords—how embarrassing! Remember that the VTY ports are default configured as login, meaning that we have to either set the VTY passwords or use the no login command. If you need to review the process of setting passwords, take a quick look back in Chapter 6, “Cisco’s Internetworking Operating System (IOS).”

If you can’t telnet into a device, it could be that the password on the remote device hasn’t been set. It’s also quite possible that an access control list is filtering the Telnet session.

---

On a Cisco device, you don’t need to use the telnet command; you can just type in an IP address from a command prompt and the router will assume that you want to telnet to the device. Here’s how that looks using just the IP address:

SW-1#10.100.128.8
Trying 10.100.128.8... Open

Password required, but none set

[Connection to 10.100.128.8 closed by foreign host]
SW-1#

Now would be a great time to set those VTY passwords on the SW-3 that I want to telnet into. Here’s what I did on the switch named SW-3:

SW-3(config)#line vty 0 15
SW-3(config-line)#login
SW-3(config-line)#password telnet
SW-3(config-line)#login
SW-3(config-line)#^Z

Now let’s try this again. This time, I’m connecting to SW-3 from the SW-1 console:

SW-1#10.100.128.8
Trying 10.100.128.8 ... Open

User Access Verification

Password:
SW-3>

Remember that the VTY password is the user-mode password, not the enable-mode password. Watch what happens when I try to go into privileged mode after telnetting into the switch:

SW-3>en
% No password set
SW-3>

It’s totally slamming the door in my face, which happens to be a really nice security feature! After all, you don’t want just anyone telnetting into your device and typing the enable command to get into privileged mode now, do you? You’ve got to set your enable-mode password or enable secret password to use Telnet to configure remote devices.

When you telnet into a remote device, you won’t see console messages by default. For example, you will not see debugging output. To allow console messages to be sent to your Telnet session, use the terminal monitor command.

---

Using the next group of examples, I’ll show you how to telnet into multiple devices simultaneously as well as how to use hostnames instead of IP addresses.

Telnetting into Multiple Devices Simultaneously

If you telnet to a router or switch, you can end the connection by typing exit at any time. But what if you want to keep your connection to a remote device going while still coming back to your original router console? To do that, you can press the Ctrl+Shift+6 key combination, release it, and then press X.

Here’s an example of connecting to multiple devices from my SW-1 console:

SW-1#10.100.128.8
Trying 10.100.128.8... Open

User Access Verification

Password:
SW-3>Ctrl+Shift+6
SW-1#

Here you can see that I telnetted to SW-1 and then typed the password to enter user mode. Next, I pressed Ctrl+Shift+6, then X, but you won’t see any of that because it doesn’t show on the screen output. Notice that my command prompt now has me back at the SW-1 switch.

Now let’s run through some verification commands.

Checking Telnet Connections

If you want to view the connections from your router or switch to a remote device, just use the showsessions command. In this case, I’ve telnetted into both the SW-3 and SW-2 switches from SW1:

SW-1#sh sessions
Conn Host            Address          Byte  Idle Conn Name
   1 10.100.128.9    10.100.128.9     0          10.100.128.9
*  2 10.100.128.8    10.100.128.8     0          10.100.128.8
SW-1#

See that asterisk (*) next to connection 2? It means that session 2 was the last session I connected to. You can return to your last session by pressing Enter twice. You can also return to any session by typing the number of the connection and then Enter.

Checking Telnet Users

You can reveal all active consoles and VTY ports in use on your router with the showusers command:

SW-1#sh users
    Line       User       Host(s)              Idle       Location
*  0 con 0                10.100.128.9         00:00:01
                          10.100.128.8         00:01:06

In the command’s output, con represents the local console, and we can see that the console session is connected to two remote IP addresses—in other words, two devices.

Closing Telnet Sessions

You can end Telnet sessions a few different ways. Typing exit or disconnect are probably the two quickest and easiest.

To end a session from a remote device, use the exit command:

SW-3>exit
[Connection to 10.100.128.8 closed by foreign host]
SW-1#

To end a session from a local device, use the disconnect command:

SW-1#sh session
Conn Host             Address           Byte  Idle Conn Name
   *2 10.100.128.9    10.100.128.9      0          10.100.128.9
SW-1#disconnect ?
  <2-2>  The number of an active network connection
  qdm    Disconnect QDM web-based clients
  ssh    Disconnect an active SSH connection
SW-1#disconnect 2
Closing connection to 10.100.128.9 [confirm][enter]

In this example, I used session number 2 because that was the connection I wanted to conclude. As demonstrated, you can use the show sessions command to see the connection number.

Resolving Hostnames

If you want to use a hostname instead of an IP address to connect to a remote device, the device that you’re using to make the connection must be able to translate the hostname to an IP address.

There are two ways to resolve hostnames to IP addresses. The first is by building a host table on each router, and the second is to build a Domain Name System (DNS) server. The latter method is similar to creating a dynamic host table assuming that you’re dealing with dynamic DNS.

Building a Host Table

An important factor to remember is that although a host table provides name resolution, it does that only on the specific router that it was built upon. The command you use to build a host table on a router looks this:

ip host host_name [tcp_port_number] ip_address

The default is TCP port number 23, but you can create a session using Telnet with a different TCP port number if you want. You can also assign up to eight IP addresses to a hostname.

Here’s how I configured a host table on the SW-1 switch with two entries to resolve the names for the SW-2 and SW-3:

SW-1#config t
SW-1(config)#ip host SW-2 ?
  <0-65535>   Default telnet port number
  A.B.C.D     Host IP address
  additional  Append addresses

SW-1(config)#ip host SW-2 10.100.128.9
SW-1(config)#ip host SW-3 10.100.128.8

Notice that I can just keep adding IP addresses to reference a unique host, one after another. To view our newly built host table, I’ll just use the show hosts command:

SW-1(config)#do sho hosts
Default domain is not set
Name/address lookup uses domain service
Name servers are 255.255.255.255

Codes: u - unknown, e - expired, * - OK, ? - revalidate
       t - temporary, p - permanent

Host                   Port  Flags      Age Type   Address(es)
SW-3                   None  (perm, OK)  0   IP    10.100.128.8
SW-2                   None  (perm, OK)  0   IP    10.100.128.9

In this output, you can see the two hostnames plus their associated IP addresses. The perm in the Flags column means that the entry has been manually configured. If it read temp, it would be an entry that was resolved by DNS.

The show hosts command provides information on temporary DNS entries and permanent name-to-address mappings created using the ip host command.

---

To verify that the host table resolves names, try typing the hostnames at a router prompt. Remember that if you don’t specify the command, the router will assume you want to telnet.

In the following example, I’ll use the hostnames to telnet into the remote devices and press Ctrl+Shift+6 and then X to return to the main console of the SW-1 router:

SW-1#sw-3
Trying SW-3 (10.100.128.8)... Open

User Access Verification

Password:
SW-3> Ctrl+Shift+6
SW-1#

It worked—I successfully used entries in the host table to create a session to the SW-3 device by using the name to telnet into it. And just so you know, names in the host table are not case-sensitive.

Notice that the entries in the following show sessions output now display the hostnames and IP addresses instead of just the IP addresses:

SW-1#sh sessions
Conn Host                Address             Byte  Idle Conn Name
   1 SW-3                10.100.128.8        0     1    SW-3
*  2 SW-2                10.100.128.9        0     1    SW-2
SW-1#

If you want to remove a hostname from the table, all you need to do is use the no ip host command like this:

SW-1(config)#no ip host SW-3

The drawback to going with this host table method is that you must create a host table on each router in order to be able to resolve names. So clearly, if you have a whole bunch of routers and want to resolve names, using DNS is a much better option!

Using DNS to Resolve Names

If you have a lot of devices, you don’t want to create a host table in each one of them unless you’ve also got a lot of time to waste. Since most of us don’t, I highly recommend using a DNS server to resolve hostnames instead!

Anytime a Cisco device receives a command it doesn’t understand, it will try to resolve it through DNS by default. Watch what happens when I type the special command todd at a Cisco router prompt:

SW-1#todd
Translating "todd"...domain server (255.255.255.255)
% Unknown command or computer name, or unable to find
  computer address
SW-1#

Because it doesn’t know my name or the command I’m trying to type, it tries to resolve this through DNS. This is really annoying for two reasons: first, because it doesn’t know my name <grin>, and second, because I need to hang out and wait for the name lookup to time out. You can get around this and prevent a time-consuming DNS lookup by using the no ip domain-lookup command on your router from global configuration mode.

So if you have a DNS server on your network, you’ll need to add a few commands to make DNS name resolution work well for you:

• The first command is ip domain-lookup, which is turned on by default. It needs to be entered only if you previously turned it off with the no ip domain-lookup command. The command can be used without the hyphen as well with the syntax ip domain lookup.
• The second command is ip name-server. This sets the IP address of the DNS server. You can enter the IP addresses of up to six servers.
• The last command is ip domain-name. Although this command is optional, you really set it because it appends the domain name to the hostname you type in. Since DNS uses a fully qualified domain name (FQDN) system, you must have a second-level DNS name, in the form domain.com.

Here’s an example of using these three commands:

SW-1#config t
SW-1(config)#ip domain-lookup
SW-1(config)#ip name-server ?
  A.B.C.D  Domain server IP address (maximum of 6)
SW-1(config)#ip name-server 4.4.4.4
SW-1(config)#ip domain-name lammle.com
SW-1(config)#^Z

After the DNS configurations have been set, you can test the DNS server by using a hostname to ping or telnet into a device like this:

SW-1#ping SW-3
Translating "SW-3"...domain server (4.4.4.4) [OK]
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.100.128.8, timeout is
  2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max
  = 28/31/32 ms

Notice that the router uses the DNS server to resolve the name.

After a name is resolved using DNS, use the show hosts command to verify that the device cached this information in the host table. If I hadn’t used the ip domain-name lammle.com command, I would have needed to type in ping sw-3.lammle.com, which is kind of a hassle.

Should You Use a Host Table or a DNS Server?

Karen has finally finished mapping her network via CDP and the hospital’s staff is now much happier. But Karen is still having a difficult time administering the network because she has to look at the network drawing to find an IP address every time she needs to telnet to a remote router.

Karen was thinking about putting host tables on each router, but with literally hundreds of routers, this is a daunting task and not the best solution. What should she do?

Most networks have a DNS server now anyway, so adding a hundred or so hostnames into it would be much easier—certainly better than adding these hostnames to each and every router! She can just add the three commands on each router and voilà—she’s resolving names!

Using a DNS server makes it easy to update any old entries too. Remember, for even one little change, her alternative would be to go to each and every router to manually update its table if she’s using static host tables.

Keep in mind that this has nothing to do with name resolution on the network and nothing to do with what a host on the network is trying to accomplish. You only use this method when you’re trying to resolve names from the router console.

---

Checking Network Connectivity and Troubleshooting

You can use the ping and traceroute commands to test connectivity to remote devices, and both of them can be used with many protocols, not just IP. But don’t forget that the show ip route command is a great troubleshooting command for verifying your routing table and the show interfaces command will reveal the status of each interface to you.

I’m not going to get into the show interfaces commands here because we’ve already been over that in Chapter 6. But I am going to go over both the debug command and the show processes command that come in very handy when you need to troubleshoot a router.

Using the ping Command

So far, you’ve seen lots of examples of pinging devices to test IP connectivity and name resolution using the DNS server. To see all the different protocols that you can use with the Ping program, type ping ?:

SW-1#ping ?
  WORD  Ping destination address or hostname
  clns  CLNS echo
  ip    IP echo
  ipv6  IPv6 echo
  tag   Tag encapsulated IP echo
  <cr>

The ping output displays the minimum, average, and maximum times it takes for a ping packet to find a specified system and return. Here’s an example:

SW-1#ping SW-3
Translating "SW-3"...domain server (4.4.4.4) [OK]
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.100.128.8, timeout is
  2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max
  = 28/31/32 ms

This output tells us that the DNS server was used to resolve the name, and the device was pinged in a minimum of 28 ms (milliseconds), an average of 31 ms, and up to 32 ms. This network has some latency!

The ping command can be used in user and privileged mode but not configuration mode!

---

Using the traceroute Command

Traceroute—the traceroute command, or trace for short—shows the path a packet takes to get to a remote device. It uses time to live (TTL), time-outs, and ICMP error messages to outline the path a packet takes through an internetwork to arrive at a remote host.

The trace command, which you can deploy from either user mode or privileged mode, allows you to figure out which router in the path to an unreachable network host should be examined more closely as the probable cause of your network’s failure.

To see the protocols that you can use with the traceroute command, type traceroute ?:

SW-1#traceroute ?
  WORD       Trace route to destination address or hostname
  appletalk  AppleTalk Trace
  clns       ISO CLNS Trace
  ip         IP Trace
  ipv6       IPv6 Trace
  ipx        IPX Trace
  mac        Trace Layer2 path between 2 endpoints
  oldvines   Vines Trace (Cisco)
  vines      Vines Trace (Banyan)
  <cr>

The traceroute command shows the hop or hops that a packet traverses on its way to a remote device.

Do not get confused! You can’t use the tracert command; that’s a Windows command. For a router, use the traceroute command!

---

Here’s an example of using tracert on a Windows prompt—notice that the command is tracert, not traceroute:

C:>tracert www.whitehouse.gov

Tracing route to a1289.g.akamai.net [69.8.201.107]
over a maximum of 30 hops:

  1     *        *        *     Request timed out.
  2    53 ms    61 ms    53 ms  hlrn-dsl-gw15-207.hlrn.qwest.net [207.225.112.207]
  3    53 ms    55 ms    54 ms  hlrn-agw1.inet.qwest.net [71.217.188.113]
  4    54 ms    53 ms    54 ms  hlr-core-01.inet.qwest.net [205.171.253.97]
  5    54 ms    53 ms    54 ms  apa-cntr-01.inet.qwest.net [205.171.253.26]
  6    54 ms    53 ms    53 ms  63.150.160.34
  7    54 ms    54 ms    53 ms  www.whitehouse.gov [69.8.201.107]

Trace complete.

Okay, let’s move on now and talk about how to troubleshoot your network using the debug command.

Debugging

Debug is a useful troubleshooting command that’s available from the privileged exec mode of Cisco IOS. It’s used to display information about various router operations and the related traffic generated or received by the router, plus any error messages.

Even though it’s a helpful, informative tool, there are a few important facts that you need to know about it. Debug is regarded as a very high-overhead task because it can consume a huge amount of resources and the router is forced to process-switch the packets being debugged. So you don’t just use debug as a monitoring tool—it’s meant to be used for a short period of time and only as a troubleshooting tool. It’s highly useful for discovering some truly significant facts about both working and faulty software and/or hardware components, but remember to limit its use as the beneficial troubleshooting tool it’s designed to be.

Because debugging output takes priority over other network traffic, and because the debug all command generates more output than any other debug command, it can severely diminish the router’s performance—even render it unusable! Because of this, it’s nearly always best to use more specific debug commands.

As you can see from the following output, you can’t enable debugging from user mode, only privileged mode:

SW-1>debug ?
% Unrecognized command
SW-1>en
SW-1#debug ?
  aaa                   AAA Authentication, Authorization and Accounting
  access-expression     Boolean access expression
  adjacency             adjacency
  aim                   Attachment Information Manager
  all                   Enable all debugging
  archive               debug archive commands
  arp                   IP ARP and HP Probe transactions
  authentication        Auth Manager debugging
  auto                  Debug Automation
  beep                  BEEP debugging
  bgp                   BGP information
  bing                  Bing(d) debugging
  call-admission        Call admission control
  cca                   CCA activity
  cdp                   CDP information
  cef                   CEF address family independent operations
  cfgdiff               debug cfgdiff commands
  cisp                  CISP debugging
  clns                  CLNS information
  cluster               Cluster information
  cmdhd                 Command Handler
  cns                   CNS agents
  condition             Condition
  configuration         Debug Configuration behavior
[output cut]

If you’ve got the freedom to pretty much take out a router or switch and you really want to have some fun with debugging, use the debug all command:

Sw-1#debug all

This may severely impact network performance. Continue? (yes/[no]):yes
All possible debugging has been turned on

At this point my switch overloaded and crashed and I had to reboot it. Try this on your switch at work and see if you get the same results. Just kidding!

To disable debugging on a router, just use the command no in front of the debug command:

SW-1#no debug all

I typically just use the undebug all command since it is so easy when using the shortcut:

SW-1#un all

Remember that instead of using the debug all command, it’s usually a much better idea to use specific commands—and only for short periods of time. Here’s an example:

S1#debug ip icmp
ICMP packet debugging is on
S1#ping 192.168.10.17

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.10.17, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/1/1 ms
S1#
1w4d: ICMP: echo reply sent, src 192.168.10.17, dst 192.168.10.17
1w4d: ICMP: echo reply rcvd, src 192.168.10.17, dst 192.168.10.17
1w4d: ICMP: echo reply sent, src 192.168.10.17, dst 192.168.10.17
1w4d: ICMP: echo reply rcvd, src 192.168.10.17, dst 192.168.10.17
1w4d: ICMP: echo reply sent, src 192.168.10.17, dst 192.168.10.17
1w4d: ICMP: echo reply rcvd, src 192.168.10.17, dst 192.168.10.17
1w4d: ICMP: echo reply sent, src 192.168.10.17, dst 192.168.10.17
1w4d: ICMP: echo reply rcvd, src 192.168.10.17, dst 192.168.10.17
1w4d: ICMP: echo reply sent, src 192.168.10.17, dst 192.168.10.17
1w4d: ICMP: echo reply rcvd, src 192.168.10.17, dst 192.168.10.17
SW-1#un all

I’m sure you can see that the debug command is one powerful command. And because of this, I’m also sure you realize that before you use any of the debugging commands, you should make sure you check the CPU utilization capacity of your router. This is important because in most cases, you don’t want to negatively impact the device’s ability to process the packets on your internetwork. You can determine a specific router’s CPU utilization information by using the show processes command.

Remember, when you telnet into a remote device, you will not see console messages by default! For example, you will not see debugging output. To allow console messages to be sent to your Telnet session, use the terminal monitor command.

---

Using the showprocesses Command

As I’ve said, you’ve really got to be careful when using the debug command on your devices. If your router’s CPU utilization is consistently at 50 percent or more, it’s probably not a good idea to type in the debug all command unless you want to see what a router looks like when it crashes!

So what other approaches can you use? Well, the show processes (or show processes cpu) is a good tool for determining a given router’s CPU utilization. Plus, it’ll give you a list of active processes along with their corresponding process ID, priority, scheduler test (status), CPU time used, number of times invoked, and so on. Lots of great stuff! Plus, this command is super handy when you want to evaluate your router’s performance and CPU utilization and are otherwise tempted to reach for the debug command!

Okay—what do you see in the following output? The first line shows the CPU utilization output for the last 5 seconds, 1 minute, and 5 minutes. The output provides 5%/0% in front of the CPU utilization for the last 5 seconds: The first number equals the total utilization, and the second one indicates the utilization due to interrupt routines. Take a look:

SW-1#sh processes
CPU utilization for five seconds: 5%/0%; one minute: 7%; five minutes: 8%
 PID QTy       PC Runtime(ms)   Invoked   uSecs    Stacks   TTY Process
   1 Cwe  29EBC58      0        22       0  5236/6000    0 Chunk Manager
   2 Csp  1B9CF10    241    206881       1  2516/3000    0 Load Meter
   3 Hwe  1F108D0      0         1       0  8768/9000    0 Connection Mgr
   4 Lst  29FA5C4 9437909    454026   20787  5540/6000    0 Check heaps
   5 Cwe  2A02468      0         2       0  5476/6000    0 Pool Manager
   6 Mst  1E98F04      0         2       0  5488/6000    0 Timers
   7 Hwe  13EB1B4   3686    101399      36  5740/6000    0 Net Input
   8 Mwe  13BCD84      0         1       0 23668/24000   0 Crash writer
   9 Mwe  1C591B4   4346     53691      80  4896/6000    0 ARP Input
  10 Lwe  1DA1504      0         1       0  5760/6000    0 CEF MIB API
  11 Lwe  1E76ACC      0         1       0  5764/6000    0 AAA_SERVER_DEADT
  12 Mwe  1E6F980      0         2       0  5476/6000    0 AAA high-capacit
  13 Mwe  1F56F24      0         1       0 11732/12000   0 Policy Manager [output cut]

So basically, the output from the show processes command reveals that our router is happily able to process debugging commands without being overloaded—nice!

Summary

In this chapter, you learned how Cisco routers are configured and how to manage those configurations.

We covered the internal components of a router, including ROM, RAM, NVRAM, and flash.

Next, you found out how to back up and restore the configuration of a Cisco router and switch.

You also learned how to use CDP and Telnet to gather information about remote devices. Finally, you discovered how to resolve hostnames and use the ping and trace commands to test network connectivity as well as how to use the debug and show processes commands—well done!

Exam Essentials

Written Lab 7

In this section, you’ll complete the following labs to make sure you’ve got the information and concepts contained within them fully dialed in:

The answers to these labs can be found in Appendix A, “Answers to Written Labs.”

Written Lab 7.1: IOS Management

Write the answers to the following questions:

Written Lab 7.2: Router Memory

Identify the location in a router where each of the following files is stored by default.

Hands-on Labs

To complete the labs in this section, you need at least one router or switch (three would be best) and at least one PC running as a TFTP server. TFTP server software must be installed and running on the PC. For this lab, it is also assumed that your PC and the Cisco devices are connected together with a switch and that all interfaces (PC NIC and router interfaces) are in the same subnet. You can alternately connect the PC directly to the router or connect the routers directly to one another (use a crossover cable in that case). Remember that the labs listed here were created for use with real routers but can easily be used with LammleSim IOS Version or Cisco’s Packet Tracer program. Last, although it doesn’t matter if you are using a switch or router in these labs, I’m just going to use my routers, but feel free to use your switch to go through these labs!

Here is a list of the labs in this chapter:

Hands-on Lab 7.1: Backing Up the Router Configuration

In this lab, you’ll back up the router configuration:

Name of configuration file to write [RouterB-confg]?

Write file RouterB-confg on host 172.16.30.2? [confirm]

Hands-on Lab 7.2: Using the Cisco Discovery Protocol (CDP)

CDP is an important objective for the Cisco exams. Please go through this lab and use CDP as much as possible during your studies.

Router#config t
Enter configuration commands, one per line.  End with
  CNTL/Z.
Router(config)#cdp timer ?
  <5-900>  Rate at which CDP packets are sent (in sec)
Router(config)#cdp timer 90

Router#sh cdp
Global CDP information:
Sending CDP packets every 90 seconds
Sending a holdtime value of 180 seconds

Router#sh cdp ?
  entry     Information for specific neighbor entry
  interface CDP interface status and configuration
  neighbors CDP neighbor entries
  traffic   CDP statistics
  <cr>

Hands-on Lab 7.3: Using Telnet

Secure Shell was covered in Chapter 6, which is what you should use for remote access into a Cisco device. However, the Cisco objectives cover telnet configuration, so let’s do a lab on telnet!

Hands-on Lab 7.4: Resolving Hostnames

It’s best to use a DNS server for name resolution, but you can also create a local hosts table to resolve names. Let’s take a look.

ip host routerb ip_address
ip host routerc ip_address

ip host routerb 172.16.20.2
ip host routerc 172.16.40.2

RouterA#ping routerb
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.16.20.2, timeout
  is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip
  min/avg/max = 4/4/4 ms

RouterA#ping routerc
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.16.40.2, timeout
  is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip
  min/avg/max = 4/6/8 ms

Default domain is not set
Name/address lookup uses domain service
Name servers are 255.255.255.255
Host                 Flags      Age Type   Address(es)
routerb             (perm, OK)  0   IP    172.16.20.2
routerc             (perm, OK)  0   IP    172.16.40.2

Review Questions

The following questions are designed to test your understanding of this chapter’s material. For more information on how to get additional questions, please see this book’s introduction.

---

The answers to these questions can be found in Appendix B, “Answers to Chapter Review Questions.”

1. Which of the following is a standards-based protocol that works much like CDP?

A. DHCP

B. LLDP

C. DDNS

D. SSTP

2. Which command can be used to determine a router’s capacity to generate debug output?

A. show version

B. show controllers

C. show processes cpu

D. show memory

3. You are troubleshooting a connectivity problem in your corporate network and want to isolate the problem. You suspect that a router on the route to an unreachable network is at fault. What IOS user exec command should you issue?

A. Router>ping

B. Router>trace

C. Router>show ip route

D. Router>show interface

E. Router>show cdp neighbors

4. You copy a configuration from a network host to a router’s RAM. The configuration looks correct, yet it is not working at all. What could the problem be?

A. You copied the wrong configuration into RAM.

B. You copied the configuration into flash memory instead.

C. The copy did not override the shutdown command in running-config.

D. The IOS became corrupted after the copy command was initiated.

5. In the following command, what does the IP address 10.10.10.254 refer to?

Router#config t
Router(config)#interface fa0/0
Router(config-if)#ip helper-address 10.10.10.254

A. IP address of the ingress interface on the router

B. IP address of the egress interface on the router

C. IP address of the next hop on the path to the DHCP server

D. IP address of the DHCP server

6. The corporate office sends you a new router to connect, but upon connecting the console cable, you see that there is already a configuration on the router. What should be done before a new configuration is entered in the router?

A. RAM should be erased and the router restarted.

B. Flash should be erased and the router restarted.

C. NVRAM should be erased and the router restarted.

D. The new configuration should be entered and saved.

7. What command can you use to determine the IP address of a directly connected neighbor?

A. show cdp

B. show cdp neighbors

C. show cdp neighbors detail

D. show neighbor detail

8. According to the output, what interface does SW-2 use to connect to SW-3?

SW-3#sh cdp neighbors 
Capability Codes: R - Router, T - Trans Bridge, B - Source Route BridgeS - Switch, H - Host, I - IGMP, r - Repeater, P - Phone, D - Remote, C - CVTA, M - Two-port Mac Relay Device ID
Local Intrfce     Holdtme    Capability  Platform  Port ID
SW-1   Fas 0/1      170          S I     WS-C3560- Fas 0/15
SW-1   Fas 0/2      170          S I     WS-C3560- Fas 0/16
SW-2   Fas 0/5      162          S I     WS-C3560- Fas 0/2

A. Fas 0/1

B. Fas 0/16

C. Fas 0/2

D. Fas 0/5

9. What command can you use to determine the IP address of a directly connected neighbor?

A. show cdp

B. show cdp neighbors

C. show cdp neighbors detail

D. show neighbor detail

10. You save the configuration on a router with the copy running-config startup-config command and reboot the router. The router, however, comes up with a blank configuration. What can the problem be?

A. You didn’t boot the router with the correct command.

B. NVRAM is corrupted.

C. The configuration register setting is incorrect.

D. The newly upgraded IOS is not compatible with the hardware of the router.

E. The configuration you saved is not compatible with the hardware.

11. If you want to have more than one Telnet session open at the same time, what keystroke combination would you use?

A. Tab+spacebar

B. Ctrl+X, then 6

C. Ctrl+Shift+X, then 6

D. Ctrl+Shift+6, then X

12. You are unsuccessful in telnetting into a remote device from your switch, but you could telnet to the router earlier. However, you can still ping the remote device. What could the problem be? (Choose two.)

A. IP addresses are incorrect.

B. Access control list is filtering Telnet.

C. There is a defective serial cable.

D. The VTY password is missing.

13. What information is displayed by the show hosts command? (Choose two.)

A. Temporary DNS entries

B. The names of the routers created using the hostname command

C. The IP addresses of workstations allowed to access the router

D. Permanent name-to-address mappings created using the ip host command

E. The length of time a host has been connected to the router via Telnet

14. Which three commands can be used to check LAN connectivity problems on a switch? (Choose three.)

A. show interfaces

B. show ip route

C. tracert

D. ping

E. dns lookups

15. You telnet to a router and make your necessary changes; now you want to end the Telnet session. What command do you type in?

A. close

B. disable

C. disconnect

D. exit

16. You telnet into a remote device and type debug ip icmp, but no output from the debug command is seen. What could the problem be?

A. You must type the show ip icmp command first.

B. IP addressing on the network is incorrect.

C. You must use the terminal monitor command.

D. Debug output is sent only to the console.

17. You need to view console messages on a device to which you have connected through telnet. The command you need to execute to see these is ___________.

18. You need to gather the IP address of a remote switch that is located in Hawaii. What can you do to find the address?

A. Fly to Hawaii, console into the switch, then relax and have a drink with an umbrella in it.

B. Issue the show ip route command on the router connected to the switch.

C. Issue the show cdp neighbor command on the router connected to the switch.

D. Issue the show ip arp command on the router connected to the switch.

E. Issue the show cdp neighbors detail command on the router connected to the switch.

19. You need to configure all your routers and switches so they synchronize their clocks from one time source. What command will you type for each device?

A. clock synchronizationip_address

B. ntp master ip_address

C. sync ntp ip_address

D. ntp server ip_address version number

20. What two commands can you use to verify your NTP client?

A. show ntp server

B. show ntp status

C. show vtp status

D. show ntp associations

E. show clock source