The Cisco Internetwork Operating System (IOS):- is the kernel of Cisco routers and most switches. The Cisco IOS is a proprietary kernel that provides routing, switching, internetworking, and tele-communications features. These are some important things that the Cisco router IOS software is responsible for:
1. Carrying network protocols and functions
2. Connecting high-speed traffic between devices
Adding security to control access and stop unauthorized network use providing scalability for ease of network growth and redundancy Supplying network reliability for connecting to network resources.
We can access the Cisco IOS through the console port of a router, from a modem into the auxiliary (or Aux) port, or even through Telnet.
Connecting to a Cisco Router
We can connect to a Cisco router to configure it, verify its configuration, and check statistics. There are different ways to do this, the first place you would connect to is the console port. The console port is usually an RJ-45 (8-pin modular) connection located at the back of the router. You can also connect to a Cisco router through an auxiliary port—which is really the same thing as a console port, the third way to connect to a Cisco router is in-band, through the program Telnet.
Bringing Up a Router
When you first bring up a Cisco router, it will run a power-on self-test (POST). If it passes, it will then look for and load the Cisco IOS from flash memory—if an IOS file is present. After that, the IOS loads and looks for a valid configuration—the startup-config—that’s stored in nonvolatile RAM, or NVRAM.
Async Async interface BVI Bridge-Group Virtual Interface CDMA-Ix CDMA Ix interface CTunnel CTunnel interface Dialer Dialer interface FastEthernet FastEthernet IEEE 802.3 Group-Async Async Group interface Lex Lex interface Loopback Loopback interface MFR Multilink Frame Relay bundle interface Multilink Multilink-group interface Null Null interface Port-channel Ethernet Channel of interfaces Serial Serial Tunnel Tunnel interface Vif PGM Multicast Host interface Virtual-PPP Virtual PPP interface Virtual-Template Virtual Template interface Virtual-TokenRing Virtual Token Ring Range interface range command
Router # config t Router (config) # hostname Todd Todd (config) # hostname Atlanta Atlanta (config) # hostname Todd Todd (config) #
Router (config) # banner? login Set login banner motd Set Message of the Day banner
Router (config) # banner motd? LINE c banner-text c, where ‘c’ is a delimiting character Router (config) # banner motd # Enter TEXT message. End with the character ‘#’.$ Acme.com network, then you must disconnect immediately. # Router (config) # ^Z Router # or Router (config) # banner motd x Unauthorized access prohibited! x
password Assign the privileged level password secret Assign the privileged level secret
aux Auxiliary line console Primary terminal line tty Terminal controller vty Virtual terminal x/y Slot/Port for Modems x/y/z Slot/Subslot/Port for Modems
Router# config t Router (config) # line aux 0 Router (config-line) password cisco Router (config-line) # login Router (config-line) # exit
Router# config t Router (config) # line consol 0 Router (config-line) password cisco Router (config-line) # login Router (config-line) # exit
Router# config t Router (config) # line vty 0 1180 Router (config-line) # password telnet Router (config-line) # login
Router# config t Router (config) # service password-encryption Router (config) # exit Router # sh run Router # config t Router (config) # no service password-encryption Router (config) # ^Z
Router (config-if) #ip address 172.16.20.2 255.255.255.0? secondary Make this IP address a secondary address < cr > Router (config-if) # ip address 172.16.20.2 255.255.255.0 secondary Router (config-if) # ^Z Router (config-if) # do sh run
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