Chapter 2

Getting Started with Cisco IOS Software

A router needs to be configured in order to operate within your network. Once it is configured, network operators often need to check the status of various router components. In this chapter you will learn about the configurable components of a router and how to use the features of the user interface to configure the router and to verify your configuration. You will also learn how to do some basic network testing using the Cisco IOS diagnostic capabilities, and how to gain remote access to other routers over the network. Finally, you will learn several techniques for manipulating configuration files.

This section will teach you how to log into the router, use the features provided by the user interface, and log out of the router again. It will also introduce the two primary modes of interacting with the router: user EXEC mode and privileged EXEC mode.

If you walk up to a router console that has been idle for some time, you will see a screen displaying the following lines.

east con0 is now available
Press RETURN to get started.

In order to begin working with the router from the console you will need to log in. If you press Enter, you will be prompted for a password.

User Access Verification
Password:
Router>

You will not see the password characters appear on the console screen.

Router>enable
Password:
Router#

To leave privileged EXEC mode and revert to user EXEC mode, use the command DISABLE.

Router#disable
Router>

Let’s log back into our router again and learn how to use the context-sensitive Help feature. This is a feature that you will learn to depend on as you work with the command-line interface.

If you want to know all the commands available to you at any time, just enter a question mark (?) at the prompt. Here is a partial listing of commands available in user EXEC mode.

This display goes on for another screen or two. The "More" at the bottom of the display means that you may see the next screen of output by pressing the space bar, or see one additional line by pressing the Enter key. Any other keypress will abort the display.

Now let’s get into privileged EXEC mode and see how this display differs.

Router>enable
Password:
Router#?
Exec commands:
access-enable Create a temporary Access-List entry
access-template Create a temporary Access-List entry
bfe For manual emergency modes setting
clear Reset functions
clock Manage the system clock
configure Enter configuration mode
connect Open a terminal connection
copy Copy configuration or image data
debug Debugging functions (see also 'undebug')
disable Turn off privileged commands
disconnect Disconnect an existing network connection
enable Turn on privileged commands
erase Erase flash or configuration memory
exit Exit from the EXEC
help DEscription of the interactive help system
lat Open a lat connection
lock Lock the terminal
login Log in as a particular user
logout Exit from the EXEC
mbranch Trace multicast route down tree branch
mrbranch Trace reverse multicast route up tree branch
--More--

Many commands you will be using have many parts or arguments. The command executive uses a real-time interpreter to execute the commands you type at the console, and it checks the syntax of each one for correctness as you enter it. You can use this syntax checking, along with the context-sensitive Help feature, to learn what information the router expects you to type at any point in any command. Let’s look at the example command, CLOCK SET.

Router#clkTranslating "clk"...domain server (255.255.255.255) % Name lookup aborted

Now I want to find out which commands begin with "cl." I can do that by typing cl?. There is no space between the "l" and the question mark.

Router#cl?
clear clock

Router#clock ? set Set the time and dateRouter#clock set ? hh:mm:ss Current TimeRouter#clock set 17:50:00 % Incomplete command.
Router#clock set 17:50:00 ?
<1-31> Day of the month
MONTH Month of the year
Router#clock set 17:50:00 1
% Incomplete command.
Router#clock set 17:50:00 1 ?
MONTH Month of the year
Router#clock set 17:50:00 1 August
% Incomplete command.
Router#clock set 17:50:00 1 August ?
<1993-2035> Year
Router#clock set 17:50:00 1 August 1998
Router#

When I get the router prompt back again with no error message I know the command was correct in syntax.

Some of the commands you will type are very long. It is helpful to know some of the keystrokes that are available to you for moving around on the line you are working on. This feature is known as enhanced editing. If you are familiar with UNIX, you will recognize these keystrokes as the emacs editing keystrokes.

• Ctrl-A go to the beginning of the line
• Ctrl-E go to the end of the line
• Esc-B go back, to the beginning of the previous word
• Esc-F go forward, to the beginning of the next word
• Ctrl-B go back one character
• Ctrl-F go forward one character

Enhanced editing also includes a feature that scrolls long lines to one side if they are longer than the terminal screen width. This is indicated by a $ next to the prompt, like so:

Router>$n extra long line to show how it scrolls under the router prompt

As soon as the line you are typing exceeds the width of the terminal screen, ten characters will appear to scroll under the router prompt. Use the Ctrl-A keystroke to get back quickly to the beginning of the line.

If you don’t want to use the enhanced editing feature, you may turn it off with the command terminal no editing. To enable it again, use the command terminal editing.

Router#show history conf t
show interfaces serial show interfaces show run clk clock set 17:50:00 clock set 17:50:00 1 clock set 17:50:00 1 August clock set 17:50:00 1 August 1998 show historyRouter#

Notice the commands are recalled exactly as they were typed, even if they were incomplete or erroneous.

Router#terminal history size 100

• a processor (CPU)
• various sorts of memory, which it uses for storing information
• an operating system, which provides functionality
• various ports and interfaces to connect it to peripheral devices or to allow it to communicate with other computers

A router has these same elements. In this section we will learn about the configurable hardware elements of the router, how to configure them, and how to check their status.

Before we power up the router we need to understand some of its components. The hardware components of the router include memory, processor, lines and interfaces.

The whole point of a router is to forward packets from one network to another, so it stands to reason that a router’s interfaces will be of primary interest to us. Interfaces are those elements that physically connect the router to various types of networks. Some of the most common router interfaces are serial (which generally connect the router to wide-area links), and the LAN interfaces: Ethernet, Token Ring, and FDDI.

The final category of router component is the one that allows us to interact with the router. We have already learned about the console port, which connects the router to a local terminal. The router also has an auxiliary port, which is often used to connect the router to a modem for out-of-band management in case the network connections are down and the console is inaccessible.

The router’s command executive has a hierarchy of modes that limit and organize the commands available to you, the user, as you configure the router. You have already learned the primary router modes, user EXEC mode and privileged EXEC mode, which can be used to check the router’s operating status and troubleshoot your network. In order to configure the router, however, we need to understand the configuration modes and how to move among them.

You cannot change the router’s configuration from user EXEC mode, so if you need to configure the router, you first must enter privileged EXEC mode.

Once you are in privileged EXEC mode, you may enter global configuration mode. This is the mode you would use to accomplish such tasks as naming your router, configuring a banner message for users logging in to the router, and enabling various routed protocols. Any configuration command that affects the operation of the entire router would be entered in global configuration mode.

Enter global configuration mode by using the command configure terminal.

Router#configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Router(config)#hostname MyRouter
MyRouter(config)#

Notice how the prompt changes to remind you that you are in global configuration mode, instead of privileged EXEC mode.

Most users want to check their running configuration right away to see if the new command is reflected in it properly. If you want to do this, remember that you can’t use any SHOW commands in global configuration mode, or in any other configuration mode for that matter. You must first exit back to privileged EXEC mode to use the SHOW commands.

Of course, you will want to configure the specific elements of your router. In order to do this you must first be in global configuration mode. All other configuration modes are entered from global configuration mode. Some of the more frequently used additional configuration modes available, with their special prompts, include:

Table 2-1 shows the most commonly used router configuration modes and how to navigate the user interface from one to another.

From time to time, you will be called upon to examine the status of your routers. Whether it is to see if a device is alive on the network, to verify the up/down status of an interface, or determine what is causing the router to go into a slowdown. The commands we use to view the status of router elements and processes are known collectively as SHOW commands.

You will need to know the basic SHOW commands that allow you to view the elements we have just discussed. One of the more commonly used SHOW commands is the show interface command. Here is an example of this command and its result.

Router1#show interface tokenRing 1
TokenRing1 is up, line protocol is up
Hardware is TMS380, address is 0000.303a.c2cd (bia 0000.303a.c2cd)
DEscription: Lab Backbone
Internet address is 172.16.1.1/26
MTU 4464 bytes, BW 16000 Kbit, DLY 630 usec, rely 255/255, load 1/255
Encapsulation SNAP, loopback not set, keepalive set (10 sec)
ARP type: SNAP, ARP Timeout 04:00:00
Ring speed: 16 Mbps
Single ring node, Source Route Transparent Bridge capable
Source bridging enabled, srn 2699 bn 1 trn 2710 (ring group)
proxy explorers disabled, spanning explorer enabled, NetBIOS cache disabled
Group Address: 0x00000000, Functional Address: 0x0880011A
Ethernet Transit OUI: 0x000000
Last input 00:00:00, output 00:00:01, output hang never
Last clearing of "show interface" counters never
Queueing strategy: fifo
Output queue 0/40, 0 drops; input queue 0/75, 0 drops
5 minute input rate 42000 bits/sec, 11 packets/sec
5 minute output rate 1000 bits/sec, 1 packets/sec
9868965 packets input, 3658968237 bytes, 0 no buffer
Received 7911721 broadcasts, 0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
2157045 packets output, 366298970 bytes, 0 underruns
0 output errors, 0 collisions, 0 interface resets
0 output buffer failures, 0 output buffers swapped out
0 transitions

The second part of this line, "line protocol is up," means that the router is detecting keepalive messages on the ring. It is possible for a carrier signal to be present, but no keepalive messages. In this case the line would read, "TokenRing1 is up, line protocol is up."

If we wanted to turn off processing on this interface without physically connecting it to the network, we could put it in an administratively down status. If we had done this, the first line of output would read, "TokenRing1 is administratively down, line protocol is down."

Each type of physical interface, such as Ethernet or serial, has slightly different information in its show interface display that is specific to that data-link technology.

Other SHOW commands that are useful are:

This command shows information about Cisco devices locally attached to this device. "Locally attached" indicates that a device is either on the same LAN segment, or connected via a serial interface. Device ID is the hostname of the advertising router. The "local Intrfce" column indicates the interface on the router whose console you are at, and the "Port ID" column indicates the attached interface on the remote router.

This command takes the previous command one step farther. This command will show all network layer addresses of the advertising interface, as well as the IOS version. CDP is an excellent troubleshooting tool to determine neighboring devices that could be causing problems due to misconfigured addresses.

In a large network with many remote locations it is impossible for a network administrator to gain physical console access to a router each time he needs to check its status or to change its configuration. It makes good sense to use the network itself to provide remote access to the routers in the network whenever possible. This is known as in-band management. Most often, the application used for remote access over an IP network is Telnet.

Every Cisco router has the Telnet application included in the IOS. This enables the administrator to establish a Telnet session into the router from any other IP host with Telnet capability, or to Telnet from the router itself to another router or IP host. You can perform most of the same configuration and status-checking functions from a Telnet session that you can perform from the router console.

Telnet sessions to or from the router are also called virtual terminal sessions. The router contains five virtual terminal lines (VTY lines), to accept incoming Telnet sessions. A Telnet session may be carried through any of the router’s physical interfaces, and attach to any of the router’s VTY lines.

In order for a router to accept an incoming Telnet session, at least one of its VTY lines must be configured with a password.

To initiate a Telnet session with a router, you must know an IP address of one of the interfaces in the router, or a symbolic name that can be resolved to an IP address in the router. The network must also be capable of routing the IP packets to that address; that is, the network portion of the address must be known to the routers in the internetwork that are between the host you are initiating the Telnet session from, and the target router.

The user interface presented by the Telnet application is identical to the interface at the router console, and is navigated in the same way.

The Cisco IOS software includes several commands that can be used to test basic connectivity in an IP network.

Ping is a tool that tests connectivity at the network layer only. It operates by sending a series of ICMP echo packets to the destination, and keeping track of the ICMP echo-replies that the destination sends back. You may use ping with its default characteristics (five 100-byte packets, two-second timeout) from user EXEC mode, but if you are in privileged EXEC mode, several other options become available to you. This is known as extended ping. Some of the other options available with extended ping include: varying the sizes of the packets, increasing the timeout value, sending more than five packets at one time, setting the "don’t fragment" bit in the IP header, and even using ping for other protocols, such as IPX and AppleTalk.

Here is sample output of a default ping. 172.20.2.1 is the IP address of our destination host.

Router1# ping 172.20.2.1
Type Escape sequence to abort.
Sending 5, 100-byte ICMP Echoes to 172.20.2.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/15/64 ms
Router1#

The series of five exclamation points indicate the response packets received successfully by our router. A dot (period), instead of an exclamation point, indicates the request timed out, either because the ICMP echo request never reached its destination, or because the response was dropped or misrouted somewhere in the network.

Another command that tests network layer connectivity is the traceroute command. Traceroute provides information about which path your traffic is taking through the internetwork, hop by hop, as well as how long each hop is taking. Here is an example of traceroute output.

Router1>trace 10.30.30.254
Type Escape sequence to abort.Tracing the route to 10.30.30.254
1 10.2.0.2 12 msec 12 msec 12 msec
2 10.1.0.1 16 msec 12 msec 8 msec
3 10.3.0.1 60 msec 56 msec *
Router1>

Debug is a tool you can use to get detailed diagnostic information from your router about routing processes and messages the router is receiving, sending, or acting upon. The debug privileged EXEC commands can provide a wealth of information about the traffic being seen (or not seen) on an interface, error messages generated by nodes on the network, protocol-specific diagnostic packets, and other useful troubleshooting data.

Great care should be taken when using the DEBUG command. By issuing a DEBUG command, you are asking the router to not only process traffic as normal, but to report information to the console or VTY session. The amount of processing power consumed by the DEBUG command varies with the quantity of information written to the console screen, which can vary dramatically according to the size and traffic load of the network. Some DEBUG commands generate a single line of output per packet, and others generate multiple lines of output per packet. Some generate large amounts of output, and others generate only occasional output. A DEBUG command that produces a large quantity of output can be very processor intensive, and may occupy so many of the routers processor cycles that it can cause network interruptions or even cause the router’s operating system to freeze or crash.

The DEBUG command is issued from privileged EXEC mode and always requires arguments. You should use the context-sensitive Help feature to discover what they are for your particular IOS version and feature set. Always be as specific about the debug output as you can in order to avoid overburdening your router. You want the minimum volume of debug output that will give you the information you are seeking.

Always remember to use the no debug or undebug all command to disable the debug output as soon as you are finished. See the following example of a debug output for an IGRP routing update being broadcast on several interfaces:

Router# debug ip igrp events
IGRP: sending update to 255.255.255.255 via Ethernet0 (172.16.1.1)
IGRP: Update contains 104 interior, 0 system, and 0 exterior routes.
IGRP: Total routes in update: 104
IGRP: Update contains 62 interior, 42 system, and 0 exterior routes.
IGRP: Total routes in update: 104
IGRP: Update contains 0 interior, 57 system, and 0 exterior routes.
IGRP: Total routes in update: 57
IGRP: sending update to 255.255.255.255 via TokenRing1 (172.17.1.1)
IGRP: Update contains 1 interior, 3 system, and 0 exterior routes.
IGRP: Total routes in update: 4
IGRP: sending update to 255.255.255.255 via TokenRing1 (192.168.23.10)
IGRP: Update contains 0 interior, 0 system, and 0 exterior routes.
IGRP: Total routes in update: 0 - suppressing null update

So as you can see, DEBUG can be a very powerful tool to determine problems with your network. But keep in mind that you can cause serious network outages if you are not careful!

Routers perform two basic functions: path determination and packet forwarding. The basic purpose of a router is to move information from one place to another. No matter what your protocol is—IP, IPX, AppleTalk, DECnet, or Vines—the purpose of the router does not change. It will perform the packet-forwarding function in the same way. When it receives a packet it will consult its routing table for that protocol to find the next-hop address that will get the packet toward its destination, and forward the packet out the interface toward that next hop.

A multiprotocol router maintains a separate routing table for each routed protocol. A routed protocol is a protocol that is used to carry user data, such as IPX or TCP/IP. A routing protocol is used only by the routers to tell each other what networks they know how to reach. A routing protocol is rarely used by host computers on a network. Routing protocols assist in the path-determination function by allowing the router to learn dynamically about the topology of the internetwork.

Routers use routing protocols to build and maintain routing tables and to forward data packets along the best path toward their destination networks. Routing protocols enable routers to learn about the status of networks that are not directly connected to them, and to communicate to other routers about the networks they are aware of. This communication is carried out on a continual basis, so the information in the routing table is updated as changes occur in the internetwork.

Routers that are neighbors on a link need to use the same routing protocol to communicate so that they can learn each other’s routes and in turn, communicate them to other neighboring routers. More than one routing protocol can be operational within a single router, although this is a practice you should avoid in designing your network, because it requires extreme care in the configuration.

The characteristics that distinguish one routing protocol from another include:

• The routed protocol for which it maintains information
• The way the routers communicate among each other
• The frequency with which this communication takes place
• The algorithm and metrics used to determine the best path

There are two basic categories of routing protocols: distance vector and link-state.

Routers configured with a distance vector protocol use frequent broadcasts of their entire routing tables on all their interfaces in order to communicate with neighboring routers. The more routes in their routing tables, the more routes that are broadcast. This limits the size of network that can use a distance vector routing protocol efficiently. The metric (measure of preferability) of one link or path when compared to another, is usually hop count. The hop count increases by one each time a packet must transit a router.

Look at Figure 2-1 to see how distance vector protocols propagate routes through the network and build their routing tables. The routing tables contain: identifiers for the individual networks, an interface within the router through which the router learned about that network, and the number of hops away the network is. "C" stands for "directly-connected."

The advantage of distance vector protocols is their extreme simplicity. Hop count metrics are easy to administer, and the distance vector protocols usually come with very few configurable parameters for tuning purposes.

The disadvantage is that hop count metrics make every link look the same, whether it is a 622-Mbps Sonet ring or a 1.544-Mbps T-1 line.

Consider Figure 2-2. If we are using a classic distance vector routing protocol to make our path determination for us, the lower path over the T-1 link will look preferable, because it is only one hop. The upper path, even though the bandwidth is about 400 times as high, will not look as good, because it takes two hops to get from Router1 to Router2.

Link-state protocols discover their neighboring routers by using a "hello" protocol, and keep track of the updates and hellos received from their neighbors. Link-state updates are usually acknowledged, so there is no need for sending out the same information again.

Convergence usually happens quickly in a link-state network, because updates are flooded immediately through the network, and are sourced by the router directly connected to the link that has changed. There is no need for each router to wait for a periodic update to transmit the new information to its neighbor.

This process is basically the same for all protocols. In most cases, a host device (PC or server) determines that it must send a packet to another host. Having acquired a gateway router's address by some means, the source host sends a packet addressed specifically to a router's physical MAC layer address, but with the protocol (network layer) address of the destination host.

On examining the packet's destination protocol address (as you recall, Layer 3) the router determines that it either knows or does not know how to forward the packet to the next hop. If the router does not know how to forward the packet, it will drop the packet. If the router knows how to forward the packet, it changes the destination physical address to that of the next hop, and transmits the packet.

The next hop may or may not be the ultimate destination host. If not, the next hop is usually another router, which executes the same switching decision process. As the packet moves through the internetwork, its physical address changes but its protocol address remains constant

Once a packet is routed to the destination, it must be placed on the LAN segment for which it was intended. The router will at that point repeat the same process as the host did before the packet was sent. The router will determine the destination host’s MAC layer address. The router will then place that host’s MAC address on the packet and forward it.

The key is that no matter what your routed protocol is, or what your routing protocol is, the routers each make independent forwarding decisions based on the routing information stored in their routing tables. The routers forward packets on a hop-by-hop basis, one step at a time.

If you are at the router console when it is powered on you should see something similar to the following:

At this point the router has loaded the bootstrap program from ROM. Next, it will load its IOS image from Flash. It first verifies the file integrity, then decompresses the image as it loads into RAM. These processes are represented by "Rs" and "#s".

Next, the router inventories and tests its interfaces. Because most of the Cisco routers come in a variety of hardware configurations, the software must be able to detect what particular interfaces are present in the router when it powers up.

Your router needs at least four passwords set for minimal security: an enable password, a console password, an auxiliary line password, and a VTY password. Unless you have configured the router to refer to a separate authentication server for this function, passwords are stored in the router’s configuration file. They can be encrypted or stored in clear text, depending on your security environment.

The primary password for router security is the enable password. This password controls access to privileged mode in your router, which allows the user to make configuration changes and do testing that could potentially disrupt network operations. By default, the enable password is not encrypted as it is stored in the configuration file.

You may have noticed during the section on the setup dialog that you are prompted for an "enable secret." The enable secret, if you have set one, overrides the enable password, and is always stored encrypted in the router’s configuration. So if you have set an enable secret, the enable password will not be used unless your router boots from an old software version (possibly stored in ROM or on a network TFTP server) that does not recognize the enable secret. It is considered a bad idea to set the enable password the same as the enable secret. This eliminates the very security benefit the enable secret is designed to provide.

By default, the router requires that passwords be set on the VTY lines in order to use them for incoming Telnet sessions. If you don’t set a password on your VTY lines and try to Telnet into the router, you will get an error message, "password required but none set." If you need those Telnet sessions for remote management, be sure to set a VTY password! If you are working in a lab environment and don’t want to type in a password each time you Telnet to a router, remove the "login" command under the VTY line configuration. This will eliminate the requirement for this password.

The default router configuration does not require passwords on the auxiliary or console lines. If you want to require passwords on these lines, you must not only set a password on them but also configure a "login" command on them. Without the "login" command, the password prompt will not appear and your password will be ignored.

In a lab or classroom environment you may choose not to set an enable password (or enable secret), but that isn’t a good idea. If you don’t set an enable password (or enable secret), the only connection from which you can get into privileged mode will be the console. That means that if you try to connect through the aux port or through a Telnet session, you won’t have any access to privileged mode if you haven’t set that enable password. There are situations in which you can be essentially locked out of the router without this password set—it has happened to me.

Cisco offers an encryption service for those passwords that normally would appear in clear text in the configuration file (not the enable secret). You can turn this on at the console by using the command, service password-encryption. Once you enter this command, each password you configure will be stored in encrypted form and cannot be recovered without a password-cracking program. This is useful if your configuration files are stored on a TFTP server; it will prevent a casual observer from determining your router passwords. It is not considered to be strong encryption, however, and will not discourage a determined hacker who wishes to break into your network.

Cisco uses the MD5 algorithm to encrypt the enable secret. There is no known way to reverse this algorithm. If you use the enable secret you will not be able to use the normal techniques for password recovery, which depend on viewing the password in clear text within the startup configuration file. You will need to reset the password, because there is no way to recover it.

• Force the system into the bootstrap program
• Select a boot source and default boot filename
• Enable or disable the console Break function
• Set the console terminal baud rate
• Load operating software from ROM
• Enable booting from a TFTP server

If the boot field value is 0x0 (all four bits set to zeros), the router will enter ROM monitor mode.

If the boot field value is 0x2 through 0xF (binary 0010 through 1111) the router will follow the normal boot sequence, and will look for boot system commands in the configuration file in NVRAM.

You can place special commands in the router’s configuration file that will instruct it where to look for its IOS image. The router will scan these entries and try to execute them in sequence when it boots up. This provides you with several fallback options in case the router’s flash memory becomes corrupted. These are called boot system commands.

Usually you will want the router to boot from flash memory. The boot system command for this is:

Router1(config)# boot system flash

If you do not specify a filename, the router loads the first valid file it finds in flash memory.

Router1(config)# boot system tftp 172.16.1.150

You may wish to have more than one TFTP server on your network that stores your backup IOS images. You may have as many "boot system TFTP" commands as you like in your router configuration for redundancy.

Router1(config)# boot system rom

This command boots the router from ROM. This is a last resort, just to get the router running so you can diagnose the problem. The system image in ROM will not have as many features and capabilities as the full IOS version in Flash, so your router may not operate in a predictable way if it boots from ROM.

The router also has the capability to copy its configuration to and from a TFTP server. This gives the network administrator the ability to store configurations out to a server for configuration tracking, change auditing, or distress recovery. You will need to store your configuration on a TFTP server if it is larger than 32,000 bytes, which is the largest configuration that can fit into NVRAM. When you TFTP a configuration to the router, you can place it in Flash, NVRAM, or RAM memory. When you place the configuration into Flash, you will still need to place it into NVRAM or RAM in order for the router to be able to use it. The COPY TFTP commands can be done via either the console or a VTY session.

The commands for copying configuration files to and from TFTP servers are as follows:

If the ping fails, verify that you have the correct IP address for the server and that the server is active (powered on), and repeat the PING command. Always remember to back up your work! Prior to downloading a new IOS or configuration file, copy the existing one in the router to the TFTP server. It is also a good idea to go to the TFTP server (or Telnet to it) and verify the exact filename as it exists on the server.

Router1# copy flash tftp c4500-js-mz.111-17a.P
IP address of remote host [255.255.255.255]? 172.20.2.1
Name of file to copy []? c4500-js-mz.111-17a.P
writing c4500-js-mz.111-17a.P !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Router1#

You may also copy an IOS image from a TFTP server into the router’s flash memory. This is accomplished by the command COPY TFTP FLASH.

Router1(config)#copy tftp flash
File name/status c4500-js-mz.111-17a.P
[123816/2097152 bytes free/total
IP address or name of remote host [255.255.255.255]? 172.20.2.1
Name of file to copy ? c4500-js-mz.112-7a.P
Copy c4500-js-mz.112-7a.P from 172.20.2.1 into Flash address space ? [confirm]<Return>
123752 bytes available for writing without erasure.
Erase Flash address space before writing? [confirm] <Return>
bank 0...zzzzzzzzzzzzzzzzvvvvvvvvvvvvvvvveeeeeeeeeeeeeeee
bank 1...zzzzzzzzzzzzzzzzvvvvvvvvvvvvvvvveeeeeeeeeeeeeeee
Loading from 172.20.2.1: !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! [OK - 1337256/2097088 bytes]
Verify checksum...vvvvvvvvvvvvvvvvvvvvVerification successful:
Length = 1337256, checksum = 0x5A1C

You are prompted for the filename of the image you want to copy. This name is case sensitive, so it pays to verify the exact name on the TFTP server. You will then be prompted for the IP address of the TFTP server. The router will verify the amount of free space in Flash memory, and will ask you if you want to erase the existing file in flash before copying the new one. Once Flash is erased, the router will load the new file from the TFTP server. Each exclamation point in the display signifies a block of the file successfully loaded. Finally the router will verify the integrity of the complete file.

The AutoInstall process is designed to configure the router automatically after connection to your wide-area network (WAN). For AutoInstall to work properly, a Transmission Control Protocol/Internet Protocol (TCP/IP) host on your network must be running as a TFTP server, and preconfigured to provide the required configuration files. The TCP/IP host can exist anywhere on the network, as long as the following two conditions are maintained:

• The host must be on the remote side of the router's synchronous serial connection to the WAN.
• User Datagram Protocol (UDP) broadcasts to and from the router and the TCP/IP host must be enabled.

Your system administrator at the site where the TCP/IP host is located coordinates this functionality. You should not attempt to use AutoInstall unless the required files have been provided on the TCP/IP host. See the appropriate software configuration publications for information on how AutoInstall works.

Use the following procedure to prepare your router for the AutoInstall process:

Taking this step saves the configuration settings that the AutoInstall process created in the router. If you fail to do this, your configuration will be lost the next time you reload the router.

The Cisco router’s user interface is a command-line interface. Router modes limit and organize the commands that are available to the user. The lowest level of access to the router is user EXEC mode, in which the user can verify router status and perform basic troubleshooting. The highest level of access is privileged EXEC mode, in which the user can change the router’s configuration and perform extensive network testing and diagnostics. The command to enter privileged EXEC mode is ENABLE. Context-sensitive Help and advanced editing features facilitate configuration and verification tasks.

The router’s configurable elements include memory (RAM, ROM, Flash, and NVRAM), interfaces for connecting to networks, and ports for user access and configuration. SHOW commands allow the user to verify the status or view the contents of these elements in an operational router.

Router modes allowing for configuration changes include global configuration mode, interface configuration mode, line configuration mode, and router configuration mode.

Cisco Discovery Protocol (CDP) allows Cisco devices to discover each other in the network regardless of whether they have network layer protocols configured. Telnet can be used to gain remote access to routers over the network. Ping and traceroute are useful to test network layer connectivity. Debug allows the user to get detailed information about almost every aspect of the router’s operation, although it must be used with great care to prevent overburdening the router.

Dynamic routing protocols can be categorized as either distance vector or link-state. Distance vector routers broadcast their entire routing tables periodically to each other. Link-state routers keep track of their neighbors, and flood updates through the network only when changes occur. Convergence is a state in which all routers in the network have a consistent view of the network topology.

When a router first powers up, it tests its hardware, locates and loads an IOS image, and applies configuration information. The startup sequence is controlled by the lowest four bits in the configuration register—the boot field. The boot field is used in conjunction with boot system commands in the configuration file to tell the router where to find its configuration information and its IOS image.

If a router does not find a valid configuration file when it boots up, it will enter the setup dialog. The setup dialog can be used to create a basic configuration for your router.

In a WAN environment, a new router can get its configuration information automatically from a TFTP server on the network. This facilitates configuration of routers at remote sites.

• The most common way to interact with the router is through the command-line interface provided by the Cisco IOS software.
• In order to begin working with the router from the console you will need to log in.
• The highest level of access to the router is privileged EXEC mode, sometimes called enable mode, because the command you use to get into this mode is ENABLE.
• To leave privileged EXEC mode and revert to user EXEC mode, use the command DISABLE.
• To log out of the router entirely and end your console session, use the command EXIT or LOGOUT.
• If you want to know all the commands available to you at any time, just enter a question mark (?) at the prompt.
• Many commands you will be using have many parts or arguments.
• The hardware components of the router include memory, processor, lines and interfaces.
• The whole point of a router is to forward packets from one network to another.
• Some of the most common router interfaces are serial (which generally connect the router to wide-area links), and the LAN interfaces: Ethernet, Token Ring, and FDDI.
• The router’s command executive has a hierarchy of modes that limit and organize the commands available to you, the user, as you configure the router.
• Once you are in privileged EXEC mode, you may enter global configuration mode.
• The commands we use to view the status of router elements and processes are known collectively as SHOW commands.
• Each type of physical interface, such as Ethernet or serial, has slightly different information in its show interface display that is specific to that data-link technology.
• Cisco Discovery Protocol (CDP) is one of the best methods of understanding your network topology. CDP is a Layer 2 media- and protocol-independent protocol that runs on all Cisco-manufactured equipment, including routers, switches, and access servers.
• In a large network with many remote locations it is impossible for a network administrator to gain physical console access to a router each time he needs to check its status or to change its configuration. . This is known as in-band management.
• Every Cisco router has the Telnet application included in the IOS.
• In order for a router to accept an incoming Telnet session, at least one of its VTY lines must be configured with a password.
• The Cisco IOS software includes several commands that can be used to test basic connectivity in an IP network.
• Ping is a tool that tests connectivity at the network layer only.
• Traceroute provides information about which path your traffic is taking through the internetwork, hop by hop, as well as how long each hop is taking.
• Debug is a tool you can use to get detailed diagnostic information from your router about routing processes and messages the router is receiving, sending, or acting upon.
• Routers perform two basic functions: path determination and packet forwarding.
• When you power up your router, it first needs to test its hardware, including memory and interfaces.
• Every Cisco router has a 16-bit configuration register, which is stored in a special memory location in NVRAM.
• You can place special commands in the router’s configuration file that will instruct it where to look for its IOS image.
• The router also has the capability to copy its configuration to and from a TFTP server.
• The AutoInstall process is designed to configure the router automatically after connection to your wide-area network (WAN).

The following Self Test questions will help you measure your understanding of the material presented in this chapter. Read all the choices carefully, as there may be more than one correct answer. Choose all correct answers for each question.