The Cisco Internetwork Operating System (IOS) is the kernel of Cisco's Routers and most of their switches.
Cisco IOS software is used to :
Carry network protocols and functions
Connect high speed traffic between devices
Add security, control access, and stop unauthorized network access
Promote Scalability for ease of network growth and redundancy
Supply network reliability for connecting to network resources
The IOS can be accessed through the console port, from a modem (auxiliary port), or through the network via telnet. Access to the IOS command line is called an EXEC session.
Console Port
Connect using a RJ-45 port on the back of the router.
Cable is wired straight through but reversed on one side (rolled cable).
Cable connects to RJ-45 to DB9 adapter and the PC uses a Terminal Emulation program set to 9600 baud, 8 bits, N parity, 1 stop bit.
Console port has no password by default.
Auxiliary Port
Same as console port and can be used in same way.
Typically used by having a modem you can use to dial into the router with.
Useful for configuring a remote router you don't have physical access to.
If a remote route stops responding, it can still be accessed if it has a modem on its auxiliary port.
Telnet
Telephone Network - it emulates a dumb terminal and connects over the network.
Can connect from PCs or other routers.
When logging on to the router, be aware that telnet sends and receives passwords and usernames in plain text.
Powering up a Cisco Router
First runs POST (Power On Self Test).
If POST passes, it loads the IOS from flash memory if present (Flash Memory is EEPROM).
IOS will then load the configuration file called startup-configuration, stored in NVRAM by default.
If no configuration file is present, the router will bring up setup mode (a step-by-step process to help you configure a router, it can be run any time by entering setup at the global configuration command line prompt).
SETUP Mode
Setup mode has two modes, Basic Management and Extended Setup.Basic Management
Only gives you enough configurations to allow connectivity to the router.
Configures only enough connectivity for management of the system.
Extended Setup
Allows you to configure some global parameters as well as interface configuration parameters.
Prompts you to configure each interface on the system.
Prompts for
Hostname
Secret Password
Enable Password
VTY Password (used for Telnet Sessions)
SNMP setup
Protocols {DECnet, AppleTalk, IP(IP routing -RIP, IGRP, etc)}
Bridging
IPX protocol
Async Lines
If ISDN BRI interface is present, it prompts for switch type.
Next configures Interfaces, including IP address and network mask.
The running-config is shown after the interfaces are configured.
The last option in setup is a menu of three choices.
1. Discard Configuration and go to command line.
To start setup mode over.
To save setup to NVRAM to be used at boot up (startup -config).
Command Line Interface
If you choose to skip setup mode, you will be taken to the command line and the status of all the interfaces will be shown to the screen.
Logging in to the Router
Depending on the port you're using, you might have to press enter to get the prompt to appear (console port). The first prompt will look like Routername> the greater than sign at the prompt tells you that you are in user mode. In user mode you can only view limited statistics of the router. To change configurations you first need to enter privileged EXEC mode. This is done by typing enable at the Routername> prompt, the prompt then changes to Routername#. This mode supports testing commands, debugging commands, and commands to manage the router configuration files. To go back to user mode type disable at the Routername# prompt. If you want to leave completely, type logout at the user mode prompt. You can also exit from the router while in privileged mode by typing exit or logout at the Routername# prompt.
Global Configuration Mode
Enter this mode from the privileged mode by typing configure terminal or conf t for short, the prompt will change to Routername(config)#. Changes made in this mode change the running-config file in DRAM. Use configure memory to change the startup-config in NVRAM. Using configure network allows you to change the configuration file on a TFTP server. If you change the memory or network config files, the router has to put them into memory (DRAM) in order to work with them, so this will change your router's current running-config file.
Interfaces
While in global configuration mode you can enter interface configuration mode and make changes to individual interfaces with the command Router(config)#interface ethernet 0 or Router(config)#int e0 for short, this enters into the interface configuration mode for Ethernet port 0 and changes the prompt to look likeRouter(config-if)#.
Subinterfaces
In global configuration mode you can create virtual interfaces, so at the prompt Routername(config)# type int e0.1 and the prompt will change to Routername(config-subif)#. For all practical purposes there isn't a limit to the amount of subinterfaces an interface can have.
Lines
In global configuration mode you can enter line [aux, vty, console] to enter commands for the line type. Changes the prompt to Routername(config-line)#. In line mode you can set passwords, inactivity timeout times, and number of available lines (vty).
Routing Protocols
In global configuration mode enter router followed by one of the following protocols: bgp Border Gateway Protocol (BGP) egp Exterior Gateway Protocol (EGP) eigrp Enhanced Interior Gateway Routing Protocol (EIGRP) igrp Interior Gateway Routing Protocol (IGRP) isis ISO IS-IS iso-igrp IGRP for OSI networks mobile Mobile routes odr On Demand stub Routes ospf Open Shortest Path First (OSPF) rip Routing Information Protocol (RIP) static Static routes
This will allow you to set parameters for the selected routing protocol and will change the current prompt to Routername(config-router)#.
Banners
There are four types of banners: exec, incoming, login, and motd. The banners are set in global configuration mode with the command: Router_2(config)#banner motd ! Enter TEXT message. End with the character '!'. Welcome to Router_2 Only authorized personnel may login ! Router_2(config)#
A delimiting character is used to set off the message, in this case the character is the ! symbol.
Adding a Description to an Interface
An interface description is limited to 80 characters and typically describes the function of the interface. Router_2(config)#int serial 1 Router_2(config-if)#description Link to East Office Router_2(config-if)#
Cisco IOS software is used to :
Carry network protocols and functions
Connect high speed traffic between devices
Add security, control access, and stop unauthorized network access
Promote Scalability for ease of network growth and redundancy
Supply network reliability for connecting to network resources
The IOS can be accessed through the console port, from a modem (auxiliary port), or through the network via telnet. Access to the IOS command line is called an EXEC session.
Console Port
Connect using a RJ-45 port on the back of the router.
Cable is wired straight through but reversed on one side (rolled cable).
Cable connects to RJ-45 to DB9 adapter and the PC uses a Terminal Emulation program set to 9600 baud, 8 bits, N parity, 1 stop bit.
Console port has no password by default.
Auxiliary Port
Same as console port and can be used in same way.
Typically used by having a modem you can use to dial into the router with.
Useful for configuring a remote router you don't have physical access to.
If a remote route stops responding, it can still be accessed if it has a modem on its auxiliary port.
Telnet
Telephone Network - it emulates a dumb terminal and connects over the network.
Can connect from PCs or other routers.
When logging on to the router, be aware that telnet sends and receives passwords and usernames in plain text.
Powering up a Cisco Router
First runs POST (Power On Self Test).
If POST passes, it loads the IOS from flash memory if present (Flash Memory is EEPROM).
IOS will then load the configuration file called startup-configuration, stored in NVRAM by default.
If no configuration file is present, the router will bring up setup mode (a step-by-step process to help you configure a router, it can be run any time by entering setup at the global configuration command line prompt).
SETUP Mode
Setup mode has two modes, Basic Management and Extended Setup.Basic Management
Only gives you enough configurations to allow connectivity to the router.
Configures only enough connectivity for management of the system.
Extended Setup
Allows you to configure some global parameters as well as interface configuration parameters.
Prompts you to configure each interface on the system.
Prompts for
Hostname
Secret Password
Enable Password
VTY Password (used for Telnet Sessions)
SNMP setup
Protocols {DECnet, AppleTalk, IP(IP routing -RIP, IGRP, etc)}
Bridging
IPX protocol
Async Lines
If ISDN BRI interface is present, it prompts for switch type.
Next configures Interfaces, including IP address and network mask.
The running-config is shown after the interfaces are configured.
The last option in setup is a menu of three choices.
1. Discard Configuration and go to command line.
To start setup mode over.
To save setup to NVRAM to be used at boot up (startup -config).
Command Line Interface
If you choose to skip setup mode, you will be taken to the command line and the status of all the interfaces will be shown to the screen.
Logging in to the Router
Depending on the port you're using, you might have to press enter to get the prompt to appear (console port). The first prompt will look like Routername> the greater than sign at the prompt tells you that you are in user mode. In user mode you can only view limited statistics of the router. To change configurations you first need to enter privileged EXEC mode. This is done by typing enable at the Routername> prompt, the prompt then changes to Routername#. This mode supports testing commands, debugging commands, and commands to manage the router configuration files. To go back to user mode type disable at the Routername# prompt. If you want to leave completely, type logout at the user mode prompt. You can also exit from the router while in privileged mode by typing exit or logout at the Routername# prompt.
Global Configuration Mode
Enter this mode from the privileged mode by typing configure terminal or conf t for short, the prompt will change to Routername(config)#. Changes made in this mode change the running-config file in DRAM. Use configure memory to change the startup-config in NVRAM. Using configure network allows you to change the configuration file on a TFTP server. If you change the memory or network config files, the router has to put them into memory (DRAM) in order to work with them, so this will change your router's current running-config file.
Interfaces
While in global configuration mode you can enter interface configuration mode and make changes to individual interfaces with the command Router(config)#interface ethernet 0 or Router(config)#int e0 for short, this enters into the interface configuration mode for Ethernet port 0 and changes the prompt to look likeRouter(config-if)#.
Subinterfaces
In global configuration mode you can create virtual interfaces, so at the prompt Routername(config)# type int e0.1 and the prompt will change to Routername(config-subif)#. For all practical purposes there isn't a limit to the amount of subinterfaces an interface can have.
Lines
In global configuration mode you can enter line [aux, vty, console] to enter commands for the line type. Changes the prompt to Routername(config-line)#. In line mode you can set passwords, inactivity timeout times, and number of available lines (vty).
Routing Protocols
In global configuration mode enter router followed by one of the following protocols: bgp Border Gateway Protocol (BGP) egp Exterior Gateway Protocol (EGP) eigrp Enhanced Interior Gateway Routing Protocol (EIGRP) igrp Interior Gateway Routing Protocol (IGRP) isis ISO IS-IS iso-igrp IGRP for OSI networks mobile Mobile routes odr On Demand stub Routes ospf Open Shortest Path First (OSPF) rip Routing Information Protocol (RIP) static Static routes
This will allow you to set parameters for the selected routing protocol and will change the current prompt to Routername(config-router)#.
Banners
There are four types of banners: exec, incoming, login, and motd. The banners are set in global configuration mode with the command: Router_2(config)#banner motd ! Enter TEXT message. End with the character '!'. Welcome to Router_2 Only authorized personnel may login ! Router_2(config)#
A delimiting character is used to set off the message, in this case the character is the ! symbol.
Adding a Description to an Interface
An interface description is limited to 80 characters and typically describes the function of the interface. Router_2(config)#int serial 1 Router_2(config-if)#description Link to East Office Router_2(config-if)#
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