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Cisco IOS

Ports on an IOS device

Cisco uses the term interface to refer to physical ports on an IOS device. Interfaces can be configured with different settings, depending on the type of the interface and whether you are configuring an interface on a router or on a switch. For example, the Cisco 7201 Router has four GE physical ports (image source: Cisco):To display the router interfaces in IOS, use the show ip int brief command from the privileged exec mode:In the output above we can see that this router has 2 physical interfaces Read more […]

Run privileged commands within global config mode

Beginning with the IOS 12.3, the privileged-exec mode commands (such as show running-configuration, show interface status, etc.) can be executed within the global configuration mode and its submodes. This allows you to execute privileged-exec mode commands without needing to exit the current configuration mode. Here is an example that explains the usefulness of this feature:In the example above you can see that we’re currently in the interface submode. We want to get more information about the Read more […]

Configure descriptions

Adding a description to an interface on a Cisco device doesn’t provide any extra functionality, but it is useful for administrative purposes, since it will help you to remember the interface function. A description of an interface is locally significant and can be up to 240 characters long. It can be set using the description command from the interface submode:DEVICE(config) interface Fa0/1 DEVICE(config-if) description WAN to LondonExample configuration:The description is displayed in the output Read more […]

show command

We’ve already mentioned a couple of show commands in the previous sections, so you should already we somewhat aware of this command. This command is used to display the device’s configuration, statistics, command history, interface status… The show command is invoked from the enable mode and can accept a lot of parameters:Floor1#show ? aaa Show AAA values access-lists List access lists arp Arp table cdp CDP information class-map Show QoS Class Map clock Display the system clock controllers Read more […]

IOS basic commands

In this article we will go through some basic IOS commands.Hostname commandThe hostname command is used to configure the device hostname. Because this command changes a device configuration, it must be entered in the global configuration mode. After typing the command, the prompt will change and display the new hostname.Here is an example that shows you how to change a hostname of a device. First, enter the global configuration mode by typing the enable command in the user EXEC mode and the configuration Read more […]

Running & startup configuration

CIsco devices store commands in two configuration files:startup configurationrunning configuration Immediately after you type a command in the global configuration mode, it will be stored in the running configuration. A running configuration resides in a device’s RAM, so if a device loses power, all configured commands will be lost.To avoid this scenario, you need to copy your current configuration into the startup configuration. A startup configuration is stored in the nonvolatile memory Read more […]

Get help in IOS

You can use the question mark to display a list of commands available in the prompt you are in:If the output spans more than one page, press the spacebar to display the following page of commands, or press Enter to go one command at a time. To quit the output, press q.To display only commands that start with a particular character or a string of characters, type the letters and then press the question mark:In the picture above you can see that we’ve displayed all commands that start with de.If Read more […]

IOS command modes

We’ve already learned that IOS has three main command modes: the user exec, privileged exec, and the global configuration modes. Each of these modes serves a different purpose and has its own set of commands. In this lesson we will describe each of this modes in more detail.User EXEC mode commandsInitially, a user logs into the User Exec mode. This is the mode with the least number of commands. You can get a list of all available commands by typing the character ?.As you can see, most of the Read more […]

Power on a Cisco device

When you first power-on a newly purchashed Cisco device, it will perform a power-on self-test (POST) to discover the hardware components and verify that all components work properly. If the POST is successful, the device will enter the setup mode. This mode presents a step-by-step dialog to help you configure some basic parameters, such as the device hostname, passwords, interface IP address, etc. To enter the setup mode, power on your device and type yes when prompted to make a selection:The wizard guides Read more […]

Backing up IOS configuration

It is always a good idea to have a backup copy of the configuration of your IOS device. IOS configurations are usually copied to a TFTP server using the copy command. You can backup both the startup configuration and the running configuration of your device. The copy commands accepts two parameters: the first parameter is the from location, and the second it the to location.TFTP is a client-server network protocol used to send and receive files. To backup files to a TFTP server, you will have to Read more […]

Cisco IOS overview

IOS (Internetwork Operating System) is a multitasking operating system used on most Cisco routers and switches. IOS has a command-line interface with the predetermined number of multiple-word commands. This operating system is used to configure routing, switching, internetworking and other features supported by a Cisco device.NOTE Previous versions of Cisco switches ran CatOS, a discounted version of a CLI-based operating sytem. Below you can see how IOS looks like when a Cisco device is started Read more […]

IOS boot sequence

The IOS boot sequence is a process performed after an Cisco IOS device is powered on. The IOS device performs a power-on self-test (POST) to test its hardware components and choose an IOS image to load. The boot sequence consists of the following steps:1. The device performs the power-on self-test (POST) process to discover and verify its hardware components.2. If the POST test is successful, the bootstrap program is copied from ROM into RAM.3. The bootstrap program decides which IOS image to load Read more […]

Pipe character in IOS

IOS supports the use of the pipe character (represented with the | character) to filter the output of the show and more commands. The pipe function takes the output of the command and sends it to another function, such as begin or include. This way, you can filter the output to find the section of the output that interests you. Here are a couple of examples:In the picture above you can see that we’ve entered the show running-config | begin interface command. This command starts the output from Read more […]