Cisco Router Configuration Tutorial

Cisco Inter-network Operating System:

Cisco IOS Modes of Operation

The Cisco IOS software provides access to several different command modes. Each command mode provides a different group of related commands.

For security purposes, the Cisco IOS software provides two levels of access to commands: user and privileged. The unprivileged user mode is called user EXEC mode. The privileged mode is called privileged EXEC mode and requires a password. The commands available in user EXEC mode are a subset of the commands available in privileged EXEC mode.

The following table describes some of the most commonly used modes, how to enter the modes, and the resulting prompts. The prompt helps you identify which mode you are in and, therefore, which commands are available to you

Mode of Operation	Usage	How to Enter the Mode	Prompt
User EXEC	Change terminal settings on a temporary basis, perform basic tests, and list system information.	First level accessed.	Router>
Privileged EXEC	System administration, set operating parameters.	From user EXEC mode, enter enable password command	Router#
Global Config	Modify configuration that affect the system as a whole.	From privileged EXEC, enter configure terminal.	Router(config)#
Interface Config	Modify the operation of an interface.	From global mode, enter interface type number.	Router(config-if)#
Setup	Create the initial configuration.	From privileged EXEC mode, enter command setup.	Prompted dialog

User EXEC Mode:

When you are connected to the router, you are started in user EXEC mode. The

user EXEC commands are a subset of the privileged EXEC commands.

Privileged EXEC Mode:

Privileged commands include the following:

•  Configure – Changes the software configuration.

•  Debug – Display process and hardware event messages.

•  Setup – Enter configuration information at the prompts.

Enter the command disable to exit from the privileged EXEC mode and return to

user EXEC mode.

Configuration Mode

Configuration mode has a set of submodes that you use for modifying interface

settings, routing protocol settings, line settings, and so forth. Use caution with

configuration mode because all changes you enter take effect immediately.

To enter configuration mode, enter the command configure terminal and exit by

pressing Ctrl-Z.

Note:

Almost every configuration command also has a no form. In general, use the no

form to disable a feature or function. Use the command without the keyword no

to re-enable a disabled feature or to enable a feature that is disabled by default.

For example, IP routing is enabled by default. To disable IP routing, enter the no

ip routing command and enter ip routing to re-enable it.

Getting Help

In any command mode, you can get a list of available commands by entering a

question mark (?).

Router>?

To obtain a list of commands that begin with a particular character sequence,

type in those characters followed immediately by the question mark (?).

Router#co?

configure connect copy

To list keywords or arguments, enter a question mark in place of a keyword or

argument. Include a space before the question mark.

Router#configure ?

memory

Configure from NV memory

network          Configure from a TFTP network host

terminal

Configure from the terminal

You can also abbreviate commands and keywords by entering just enough

characters to make the command unique from other commands. For example,

you can abbreviate the show command to sh.

Configuration Files

Any time you make changes to the router configuration, you must save the

changes to memory because if you do not they will be lost if there is a system

reload or power outage. There are two types of configuration files: the running

(current operating) configuration and the startup configuration.

Use the following privileged mode commands to work with configuration files.

•     configure terminal – modify the running configuration manually

from the terminal.

•     show running-config – display the running configuration.

•     show startup-config – display the startup configuration.

•     copy running-config startup-config – copy the running

configuration to the startup configuration.

•     copy startup-config running-config – copy the startup

configuration to the running configuration.

•     erase startup-config – erase the startup-configuration in NVRAM.

•     copy tftp running-config – load a configuration file stored on a

Trivial File Transfer Protocol (TFTP) server into the running

configuration.

•     copy running-config tftp – store the running configuration on a

TFTP server.

IP Address Configuration

Take the following steps to configure the IP address of an interface.

Step 1: Enter privileged EXEC mode:

Router>enable password

Step 2: Enter the configure terminal command to enter global configuration

mode.

Router#config terminal

Step 3: Enter the interface type slot/port (for Cisco 7000 series) or interface

type port (for Cisco 2500 series) to enter the interface configuration mode.

Example:

Router (config)#interface ethernet 0/1

Step 4: Enter the IP address and subnet mask of the interface using the ip

address ipaddress subnetmask command.

Example,

Router (config-if)#ip address 192.168.10.1 255.255.255.0

Step 5: Exit the configuration mode by pressing Ctrl-Z

Router(config-if)#[Ctrl-Z]

Routing Protocol Configuration

Routing Information Protocol (RIP)

Step 1: Enter privileged EXEC mode:

Router>enable password

Step 2: Enter the configure terminal command to enter global configuration

mode.

Router#config terminal

Step 3: Enter the router rip command

Router(config)#router rip

Step 4: Add the network number to use RIP and repeat this step for all the

numbers.

Router(config-router)#network network-number

Example: Router(config-router)#network 192.168.10.0

Note: To turn off RIP, use the no router rip command.

Router(config)#no router rip

Other useful commands

•  Specify a RIP Version

By default, the software receives RIP version 1 and version 2 packets, but sends

only version 1 packets. To control which RIP version an interface sends, use one

of the following commands in interface configuration mode:


Cisco router configuration tutorial

Command	Purpose
ip rip send version 1	Configure an interface to send only RIP version 1 packets.
ip rip send version 2	Configure an interface to send only RIP version 2 packets.
ip rip send version 1 2	Configure an interface to send only RIP version 1 and version 2 packets.

To control how packets received from an interface are processed, use one of the following commands:

Command	Purpose
ip rip receive version 1	Configure an interface to accept only RIP version 1 packets.
ip rip receive version 2	Configure an interface to accept only RIP version 2 packets
ip rip receive version 1 2	Configure an interface to accept only RIP version 1 or 2 packets.

• Enable or Disable Split Horizon

Use one of the following commands in interface configuration mode:

Command	Purpose
ip split-horizon	Enable split horizon.
no ip split-horizon	Disable split horizon.

Open Shortest Path First (OSPF)

Step 1: Enter privileged EXEC mode:

Router>enable password

Step 2: Enter the configure terminal command to enter global configuration mode.

Router#config terminal

Step 3: Enter the router ospf command and follow by the process-id.

Router(config)#router ospf process-id

Pick the process-id which is not being used. To determine what ids are being used, issue the show process command.

Router(config)#show process

Step 4: Add the network number, mask and area-id

Router(config-router)#network network-number mask area area-id

The network-number identifies the network using OSPF. The mask tells which bits to use from the network-number, and the area-id is used for determining areas in an OSPF configuration.

Example:

Router(config-router)#network 192.168.10.0 255.255.255.0 area 0.0.0.0

Repeat this step for all the network numbers.

To turn off OSPF, use the following command.

Router(config)#no router ospf process-id

Other useful commands

• Configure OSPF Interface Parameters

You are not required to alter any of these parameters, but some interface parameters must be consistent across all routers in an attached network.

In interface configuration mode, specify any of the following:

Command	Purpose
ip ospf cost cost	Explicitly specify the cost of sending a packet on an OSPF interface.
ip ospf retransmit-interval seconds	Specify the number of seconds between link state advertisement retransmissions for adjacencies belonging to an OSPF interface.
ip ospf transmit-delay seconds	Set the estimated number of seconds it takes to transmit a link state update packet on an OSPF interface.
ip ospf priority number	Set router priority to help determine the OSPF designated router for a network.
ip ospf hello-interval seconds	Specify the length of time, in seconds, between the hello packets that a router sends on an OSPF interface.
ip ospf dead-interval seconds	Set the number of seconds that a router’s hello packets must not have been seen before its neighbors declare the OSPF router down.
ip ospf authentication-key password	Assign a specific password to be used by neighboring OSPF routers on a network segment that is using OSPF’s simple password authentication.

Interior Gateway Routing Protocol (IGRP)


• Create the IGRP Routing Process

To create the IGRP routing process, use the following required commands starting in global configuration mode.

Step	Command	Purpose
1	router igrp autonomous-system	Enable an IGRP routing process, which place you in router configuration mode.
2	network network-number	Associate networks wit

• Disable Holddown

The holddown mechanism is used to help avoid routing loop in the network, but has the effect of increasing the topology convergence time.

To disable holddowns with IGRP, use the following command in router configuration mode. All devices in an IGRP autonomous system must be consistent in their use of holddowns.

Command	Purpose
No metric holddown	Disable the IGRP holddown period.

• Enforce a Maximum Network Diameter

Define a maximum diameter to the IGRP network. Routes whose hop counts exceed this diameter are not advertised. The default maximum diameter is 100 hops. The maximum diameter is 255 hops.

Use the following command in router configuration mode.

Command	Purpose
metric maximum-hops hops	Configure the maximum network diameter.

• To turn off IGRP, use the following command.

Router(config)#no router igrp autonomous-system

Border Gateway Protocol (BGP)

• Enable BGP Routing

Use the following commands in global configuration mode.

Step	Command	Purpose
1	router bgp autonomous-system	Enable a BGP routing process, which places you in router configuration mode.
2	network network-number [mask network-mask] [route-map route-map-name]	Flag a network as local to this autonomous system and enter it to the BGP table.

• Configure BGP Neighbors

BGP must completely understand the relationships it has with its neighbors.

Command	Purpose
neighbor {ip-address | peer-group-name} remote-as number	Specify a BGP neighbor.

• Reset BGP Connections

Use either of the following commands in EXEC mode to reset BGP connections

Command	Purpose
clear ip bgp address	Reset a particular BGP connection.
clear ip bgp *	Reset all BGP connections.

• To turn off BGP, use the following command.

Router(config)#no router bgp autonomous-system

How to read router/link status

Status of router and links can be easily determined by power LED of router and link LED of each interface (if any). However, you may find a transceiver connected to an AUI port looks like the following:

When this transceiver is correctly connected, the “POWER” LED should light. Similarly, the “LINK” and “POLARITY” LEDs should light when you inserted the cable into the RJ45 socket on the transceiver. (Note that to get this result; the other end of the cable should be connected to some other devices as well.) If these LEDs are not light, you probably have problems with the link (cable).

Can I host my web site on my home/office computer?

That’s an interesting question…

Let me first give you a quick answer before I bore you with details.
Yes, you CAN host a web site on your home/office computer.

And why do I think it is an interesting question – Because, unfailingly, at least one student from my beginners class throws this at me and so I guess it’s something that everyone wants to know. Also the answer to this question helps us to know, in a little bit more detail, what web servers are and how they work.

Let me rephrase the question – Why can’t our home computers with broadband internet and 24/7 connectivity be used as web Servers and host web sites? Actually, our home computers CAN act like web servers. Here are a few things we need:

• A static I.P. (Internet protocol) address
• 24/7 Internet connectivity (a fast connection would definitely help)
• Web server software
• A stable and reliable operating system

Hosting your web site from your home/office computer

Typically, a web server is a powerful machine with a stable and reliable operating system and a 24/7 Internet connection. A web server also needs a static I.P. (Internet protocol) address so that the location of the hosted web site/s does not change. In addition to the web server software (which serves web pages), several other software that help in maintenance, enhancing functionality and securing the machine from attacks from hackers need to be installed on the machine.

The need for a good operating system

Obviously, you need a stable and reliable operating system that can serve web pages quickly and not crash or hang even under heavy traffic. Here are some other hallmarks of a good operating system for a web server:

• In-built security features to protect from hackers and virus attacks.
• Easy of administration through shell environment or GUI-based software.
• Scalability to up-gradations to ensure enhanced stability and security. Also, the process of installation of updates should easy and as smooth as possible.
• In-built necessary server software should be a part of the operating system else, they should be available and installed quickly and smoothly.
• Availability of third-party software – No operating system is perfect and complete. Third party applications can provide additional security, better features and functionality.

With the above points in mind, the Linux operating system fits the bill pretty well – So does Windows, actually, but you do need to be a little more experienced in server administration if you want to run a Windows based web server.

Linux is also cheaper than Windows and has tons of free third-party software and applications that can be smoothly integrated in the operating system to increase functionality and security. Linux, which is an Open Source Software (OSS), works well with other OSS such as Apache (the most popular web server software), MySQL (a good stable database application and server), PHP (server-side scripting language) and has several in-built applications such as FTP (File Transfer Protocol), sendmail (SMTP email server) etc.

The need for a static I.P. (Internet Protocol) address

Each computer connected to the Internet needs to have a unique number assigned to it so that it can be identified and there are no conflicts with other computers. This unique number is the Internet Protocol (I.P.) address. The I.P. address is just a series of four numbers each less than 255 and separated by dots (periods). For example, 214.34.7.90 would be a valid I.P. address.

Since, for us humans, I.P. addresses are not as easy to remember, the “powers that be” created domain names. However, each domain name is “tied up” or “associated” with an I.P. address. The domain name and its corresponding I.P. address are stored on several different computers scattered around the globe. These machines called Domain Name Servers help to resolve the domain name to its I.P. address. In layman’s language – when you type a domain name on your browser, it first checks with a Name Server and gets the corresponding I.P. address (something that computers understand better than us) and then loads the web site.

An I.P. address is the address of a computer on the internet – it specifies the location of a server that hosts a web site. It follows that if the I.P. address changes, the web site will not be found if you try to load it on a browser by typing its domain name.

Now, most of us use net connections on our home/office computers from the local Internet Service Provider. These ISPs assigned our computers with a dynamic I.P. address each time we connect. Thus, each time we disconnect and start the connection again, our computers are given a different I.P. address. So if the I.P. address of your home/office computer changes, your web site will not load unless you go and change the information on the Name Server. Obviously you cannot make these changes each time your computer’s I.P. address changes. For this reason, to host a web site on your home/office computer you need a “static” I.P. address – an I.P. address that does not change.

The problem is that ISPs generally do not allow you to host a web site on your computer. And they do this by allocating a new I.P. address each time you connect and also blocking required ports. Having said that, you can get a static I.P. addresses by either upgrading your package (to something like a “business package”) or shift to an ISP that does provides one. The cost of a static I.P. can be an extra $30 to $50 per month (maybe even more). Check with your Internet Service Provider. This, in my opinion, is just too much when web hosting companies offer feature-rich packages for as low as $10 per month.

Also check DynDNS.com if you want a static I.P. from a dynamic address. FYI, some ISPs would actually fine you if you host a web site on their net connection.

The need for 24/7 connectivity to the Internet

A fast Internet connection is as important as a stable 24/7 connection. You would not like your web site to download slowly would you? Any downtime in the net connection would result in your web site being offline.

The need for Server software

According to Netcraft server statistics, Apache still is the most popular and widely used web server on the net. Apache is an open source software (read free) that can be installed on various platforms including Linux/Unix, Windows, Mac. For more details on Apache refer – What is Apache and what does it do?.

You can also have a look at a detailed list of important web servers.

Its easy to install the Apache web server. In fact, most Linux versions come with an Apache server already running or one that can be installed and configured in a few clicks.

The need configuring your computer for security and accessibility

If you plan to host a web site on your home/office you cannot leave it open to attacks by hackers. Also you need to protect important directories – ones containing files of the operating system or other programs that are critical for smooth and error-free running of the server. Your system has to be configured properly to protect against accidental or intentional misuse.

The final conclusions

Hosting your web site on your home/office computer would be a great learning experience to all adventurous people out there. For most of us, it’s wiser and quicker to just go to a reliable hosting company and pick up a web hosting package because these companies take care of maintaining the server, the internet connection, server security and power backups.