1.2 Clasify Network Protocol and Communication

Cisco IOS (Internetwork Operating System) is a proprietary operating system that runs on Cisco Systems routers and switches. The core function of Cisco IOS is to enable data communications between network nodes.

In addition to routing and switching, Cisco IOS offers dozens of additional services that an administrator can use to improve the performance and security of network traffic.

Such services include encryption, authentication, firewall capabilities, policy enforcement, deep packet inspection, Quality of Service (QoS), intelligent routing and proxy capability. In Cisco's Integrated Services Routers (ISRs), IOS can also support call processing and unified communications services.

Cisco IOS software releases are organized into what Cisco calls "families" and "trains." Each family shares the same code base and trains are how new IOS releases are delivered

There are two types of IOS operating systems:

IOS XE - runs on top of a Linux kernel. IOS XE and IOS share a lot of the same code, but IOS XR is considered to be a completely different code base.

IOS XR - based on QNX a commercial Unix-like real-time operating system. IOS XR supports software-defined networking (SDN) and the embedded systems market.

There are three most common ways to access the IOS:

The purpose of the Cisco
IOS.

  1. Console access – this type of access is usually used to configure newly acquired devices. These devices usually don’t have an IP address configured, and therefore can not be accessed through the network. Most of the Cisco devices have a physical console port. This port can be connected to a computer using a rollover cable, a special type of cable with pins on one end reversed on the other end of the cable. The rollover cable is a serial cable, which means that you can’t just plug it in an Ethernet port on your computer. You will need an adapter that converts an interface on your computer (usually a 9-pin serial interface) into RJ-45.
  1. Telnet access – this type of access used to be a common way to access network devices. Telnet is an terminal emulation program that enables you to access IOS through the network and configure the device remotely. The device that is being configured needs to have an Telnet server installed and an IP address configured. Telnet uses a well known TCP port 23. One of the biggest disadvantages of this protocol is that is sends all data as clear-text, which includes the passwords! This is the reason why this type of access is usually not used anymore. Instead, SSH is usually used.
  1. SSH access – like Telnet, this access type enables you to configure devices remotely, but it adds an extra layer of security by encrypting all communications using public-key cryptography. SSH uses well known TCP port 22.

How to access a Cisco IOS
device for configuration purposes.

Basic IOS Command Structure-A network administrator must know the basic IOS command structure to be able to use the CLI for device configuration.


A Cisco IOS device supports many commands. Each IOS command has a specific format, or syntax, and can only be executed in the appropriate mode. The general syntax for a command, shown in the figure, is the command followed by any appropriate keywords and arguments.

Basic-IOS-Command-Structure

Keyword – This is a specific parameter defined in the operating system (in the figure, ip protocols).

Argument – This is not predefined; it is a value or variable defined by the user (in the figure, 192.168.10.5).

After entering each complete command, including any keywords and arguments, press the Enter key to submit the command to the command interpreter.

IOS Command Syntax Check-A command might require one or more arguments. To determine the keywords and arguments required for a command, refer to the command syntax. The syntax provides the pattern, or format, that must be used when entering a command.As identified in the table, boldface text indicates commands and keywords that are entered as shown. Italic text indicates an argument for which the user provides the value.

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Describe the command structure
of the Cisco IOS software.

Devices and media are the physical elements or hardware of the network. Hardware is often the visible components of the network platform such as a laptop, a PC, a switch, or the cabling used to connect the devices. Occasionally, some components may not be so visible. In the case of wireless media, messages are transmitted through the air using invisible radio frequency or infrared waves.

Services and processes are the communication programs, called software, that run on the networked devices. A network service provides information in response to a request. Services include many of the common network applications people use every day, like e-mail hosting services and web hosting services. Processes provide the functionality that directs and moves the messages through the network. Processes are less obvious to us but are critical to the operation of networks.

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How devices communicate
across network media