Routers & Cisco IOS

Introduction to Routers A router is a special type of computer. It has the same basic components as a standard desktop PC. However, routers are designed to perform some very specific functions. Just as computers need operating systems to run software applications, routers need the Internetwork Operating System software (IOS) to run configuration files. These configuration files contain the instructions and parameters that control the flow of traffic in and out of the routers. The many parts of a router are shown below:

RAM Random Access Memory, also called dynamic RAM (DRAM) RAM has the following characteristics and functions: Stores routing tables Holds ARP cache Holds fast-switching cache Performs packet buffering (shared RAM) Maintains packet-hold queues Provides temporary memory for the configuration file of the router while the router is powered on Loses content when router is powered down or restarted

NVRAM Non-Volatile RAM NVRAM has the following characteristics and functions: Provides storage for the startup configuration file Retains content when router is powered down or restarted

Flash Flash memory has the following characteristics and functions: Holds the operating system image (IOS) Allows software to be updated without removing and replacing chips on the processor Retains content when router is powered down or restarted Can store multiple versions of IOS software Is a type of electronically erasable, programmable ROM (EEPROM)

ROM Read-Only Memory ROM has the following characteristics and functions: Maintains instructions for power-on self test (POST) diagnostics Stores bootstrap program and basic operating system software Requires replacing pluggable chips on the motherboard for software upgrades

Interfaces Interfaces have the following characteristics and functions: Connect router to network for frame entry and exit Can be on the motherboard or on a separate module Types of interfaces: Ethernet Fast Ethernet Serial Token ring ISDN BRI Loopback Console Aux

Internal Components of a 2600 Router

External Components of a 2600 Router

External Connections

Fixed Interfaces When cabling routers for serial connectivity, the routers will either have fixed or modular ports. The type of port being used will affect the syntax used later to configure each interface. Interfaces on routers with fixed serial ports are labeled for port type and port number.

Modular Serial Port Interfaces Interfaces on routers with modular serial ports are labeled for port type, slot, and port number.The slot is the location of the module.To configure a port on a modular card, it is necessary to specify the interface using the syntax “port type slot number/port number.” Use the label “serial 0/1,” when the interface is serial, the slot number where the module is installed is slot 0, and the port that is being referenced is port 1.

Routers & DSL Connections The Cisco 827 ADSL router has one asymmetric digital subscriber line (ADSL) interface. To connect a router for DSL service, use a phone cable with RJ-11 connectors. DSL works over standard telephone lines using pins 3 and 4 on a standard RJ-11 connector.

Computer/Terminal Console Connection

Modem Connection to Console/Aux Port

HyperTerminal Session Properties

Establishing a HyperTerminal Session Take the following steps to connect a terminal to the console port on the router: First, connect the terminal using the RJ-45 to RJ-45 rollover cable and an RJ-45 to DB-9 or RJ-45 to DB-25 adapter. Then, configure the terminal or PC terminal emulation software for 9600 baud, 8 data bits, no parity, 1 stop bit, and no flow control.

Cisco IOS Cisco technology is built around the Cisco Internetwork Operating System (IOS), which is the software that controls the routing and switching functions of internetworking devices. A solid understanding of the IOS is essential for a network administrator.

The Purpose of Cisco IOS As with a computer, a router or switch cannot function without an operating system. Cisco calls its operating system the Cisco Internetwork Operating System or Cisco IOS. It is the embedded software architecture in all of the Cisco routers and is also the operating system of the Catalyst switches. Without an operating system, the hardware does not have any capabilities. The Cisco IOS provides the following network services: Basic routing and switching functions Reliable and secure access to networked resources Network scalability

Router Command Line Interface

Setup Mode Setup is not intended as the mode for entering complex protocol features in the router. The purpose of the setup mode is to permit the administrator to install a minimal configuration for a router, unable to locate a configuration from another source.  In the setup mode, default answers appear in square brackets [ ] following the question. Press the Enter key to use these defaults. During the setup process, Ctrl-C can be pressed at any time to terminate the process. When setup is terminated using Ctrl-C, all interfaces will be administratively shutdown. When the configuration process is completed in setup mode, the following options will be displayed: [0] Go to the IOS command prompt without saving this config. [1] Return back to the setup without saving this config. [2] Save this configuration to nvram and exit. Enter your selection [2]:

Operation of Cisco IOS Software The Cisco IOS devices have three distinct operating environments or modes: ROM monitor Boot ROM Cisco IOS The startup process of the router normally loads into RAM and executes one of these operating environments. The configuration register setting can be used by the system administrator to control the default start up mode for the router. To see the IOS image and version that is running, use the show version command, which also indicates the configuration register setting.

IOS File System Overview

Initial Startup of Cisco Routers A router initializes by loading the bootstrap, the operating system, and a configuration file. If the router cannot find a configuration file, it enters setup mode. Upon completion of the setup mode a backup copy of the configuration file may be saved to nonvolatile RAM (NVRAM). The goal of the startup routines for Cisco IOS software is to start the router operations. To do this, the startup routines must accomplish the following: Make sure that the router hardware is tested and functional. Find and load the Cisco IOS software. Find and apply the startup configuration file or enter the setup mode. When a Cisco router powers up, it performs a power-on self test (POST). During this self test, the router executes diagnostics from ROM on all hardware modules.

After the Post… After the POST, the following events occur as the router initializes: Step 1 The generic bootstrap loader in ROM executes. A bootstrap is a simple set of instructions that tests hardware and initializes the IOS for operation.  Step 2 The IOS can be found in several places. The boot field of the configuration register determines the location to be used in loading the IOS. If the boot field indicates a flash or network load, boot system commands in the configuration file indicate the exact name and location of the image. Step 3 The operating system image is loaded. Step 4 The configuration file saved in NVRAM is loaded into main memory and executed one line at a time. The configuration commands start routing processes, supply addresses for interfaces, and define other operating characteristics of the router. Step 5 If no valid configuration file exists in NVRAM, the operating system searches for an available TFTP server. If no TFTP server is found, the setup dialog is initiated.  

Step in Router Initialization

Router LED Indicators Cisco routers use LED indicators to provide status information. Depending upon the Cisco router model, the LED indicators will vary. An interface LED indicates the activity of the corresponding interface. If an LED is off when the interface is active and the interface is correctly connected, a problem may be indicated. If an interface is extremely busy, its LED will always be on. The green OK LED to the right of the AUX port will be on after the system initializes correctly.

Enhanced Cisco IOS Commands

The show version Command The show version command displays information about the Cisco IOS software version that is currently running on the router. This includes the configuration register and the boot field settings. The following information is available from the show version command: IOS version and descriptive information Bootstrap ROM version Boot ROM version Router up time Last restart method System image file and location Router platform Configuration register setting Use the show version command to identify router IOS image and boot source. To find out the amount of flash memory, issue the show flash command.

Checking File System Information with show version command

Router Configuration

Router User Interface Modes The Cisco command-line interface (CLI) uses a hierarchical structure. This structure requires entry into different modes to accomplish particular tasks. Each configuration mode is indicated with a distinctive prompt and allows only commands that are appropriate for that mode. As a security feature the Cisco IOS software separates sessions into two access levels, user EXEC mode and privileged EXEC mode. The privileged EXEC mode is also known as enable mode.

Overview of Router Modes

Router Modes

User Mode Commands

Privileged Mode Commands NOTE: There are many more commands available in privileged mode.

Specific Configuration Modes

CLI Command Modes All command-line interface (CLI) configuration changes to a Cisco router are made from the global configuration mode. Other more specific modes are entered depending upon the configuration change that is required. Global configuration mode commands are used in a router to apply configuration statements that affect the system as a whole. The following command moves the router into global configuration mode Router#configure terminal (or config t) Router(config)# When specific configuration modes are entered, the router prompt changes to indicate the current configuration mode. Typing exit from one of these specific configuration modes will return the router to global configuration mode. Pressing Ctrl-Z returns the router to all the way back privileged EXEC mode.

Configuring a Router’s Name A router should be given a unique name as one of the first configuration tasks. This task is accomplished in global configuration mode using the following commands: Router(config)#hostname Tokyo Tokyo(config)# As soon as the Enter key is pressed, the prompt changes from the default host name (Router) to the newly configured host name (which is Tokyo in the example above).

Configuring a Router’s Name A router should be given a unique name as one of the first configuration tasks. This task is accomplished in global configuration mode using the following commands: Router(config)#hostname Tokyo Tokyo(config)# As soon as the Enter key is pressed, the prompt changes from the default host name (Router) to the newly configured host name (which is Tokyo in the example above).

Setting the Clock with Help

Message Of The Day (MOTD) A message-of-the-day (MOTD) banner can be displayed on all connected terminals. Enter global configuration mode by using the command config t Enter the command banner motd # The message of the day goes here #. Save changes by issuing the command copy run start

Configuring a Console Password Passwords restrict access to routers. Passwords should always be configured for virtual terminal lines and the console line. Passwords are also used to control access to privileged EXEC mode so that only authorized users may make changes to the configuration file. The following commands are used to set an optional but recommended password on the console line: Router(config)#line console 0 Router(config-line)#password <password> Router(config-line)#login

Configuring a Modem Password If configuring a router via a modem you are most likely connected to the aux port. The method for configuring the aux port is very similar to configuring the console port. Router(config)#line aux 0 Router(config-line)#password <password> Router(config-line)#login

Configuring Interfaces An interface needs an IP Address and a Subnet Mask to be configured. All interfaces are “shutdown” by default. The DCE end of a serial interface needs a clock rate. Router#config t Router(config)#interface serial 0/1 Router(config-if)#ip address 200.100.50.75 255.255.255.240 Router(config-if)#clock rate 56000 (required for serial DCE only) Router(config-if)#no shutdown Router(config-if)#exit Router(config)#int f0/0 Router(config-if)#ip address 150.100.50.25 255.255.255.0 Router(config-if)#no shutdown Router(config)#exit Router# On older routers, Serial 0/1 would be just Serial 1 and f0/0 would be e0. s = serial e = Ethernet f = fast Ethernet

Configuring a Telnet Password A password must be set on one or more of the virtual terminal (VTY) lines for users to gain remote access to the router using Telnet. Typically Cisco routers support five VTY lines numbered 0 through 4. The following commands are used to set the same password on all of the VTY lines: Router(config)#line vty 0 4 Router(config-line)#password <password> Router(config-line)#login

Examining the show Commands There are many show commands that can be used to examine the contents of files in the router and for troubleshooting. In both privileged EXEC and user EXEC modes, the command show ? provides a list of available show commands. The list is considerably longer in privileged EXEC mode than it is in user EXEC mode. show interfaces – Displays all the statistics for all the interfaces on the router. show int s0/1 – Displays statistics for interface Serial 0/1 show controllers serial – Displays information-specific to the interface hardware show clock – Shows the time set in the router show hosts – Displays a cached list of host names and addresses show users – Displays all users who are connected to the router show history – Displays a history of commands that have been entered show flash – Displays info about flash memory and what IOS files are stored there show version – Displays info about the router and the IOS that is running in RAM show ARP – Displays the ARP table of the router show start – Displays the saved configuration located in NVRAM show run – Displays the configuration currently running in RAM show protocol – Displays the global and interface specific status of any configured Layer 3 protocols

The copy run tftp Command

The copy tftp run Command