Configuring The IOS

Using Lines to Configure The IOS: 

Lines identify ports that allow us to connect into, and then configure, Cisco devices. There are three methods (or lines) to configure cisco IOS devices.

1. Console ports: Nearly, every modern Cisco router or switch includes a console port, sometimes labeled on the device simply as con. The console port is generally a RJ-45 connector, and requires a rollover cable to connect to. The opposite side of the rollover cable connects to a PC's serial port using a serial terminal adapter.
             From the PC, software such as HyperTerminal is required to make a connection from the local serial port to the router console port. The following settings are necessary for a successful connection:

• Bits per second - 9600
• Data bits - 8
• Parity -  None
• Stop bits - 1
• Flow Control - Hardware

2. Auxiliary port:  The auxiliary port can function similarly to a console port, and can be accessed using a rollover cable. Additionally, auxiliary ports support modem commands, thus providing dial-in access to Cisco Devices.


3. Telnet (VTY) ports:  Telnet, and now SSH, are the most common methods of remote access to routers and switches. The standard edition of the IOS supports up to 5 simultaneous VTY connections. Enterprise editions of the IOS supports up to 255 VTY connections.
                These are two requirements before a router/switch will accept a VTY connection:
a) An IP address must be configured on an interface.
b) Atleast one VTY port must be configured with a password.

Cisco IOS

The Cisco IOS is a command-line interface used by nearly all current Cisco routers and Catalyst switches. The IOS provides the mechanism to configure all layer 2 and layer 3 functions on Cisco devices.
                          The IOS is structured into several modes, which contain sets of commands specific to the function of that mode. Access to a specific mode (and specific commands) is governed by privilege mode.

The following is a representation of the IOS command-line interface, with an example command:

                       Router#show startup-config

Router--------------------> Hostname
# -------------------------> Mode
show ---------------------> Command
startup-config -------------> Argument

Hitting the "enter" key after a command will usually yield output specific to your command.

IOS version Numbers:
  IOS version numbers are formatted as follows:
                                  x.y(z)t

• "x" designates a major revision number.
• "y" designates a minor revision number.
• "z" designates an individual release number.
•  "t" designates a train identifier

Train Identifiers:

• "T" or technology train is continously updated with new features and security fixes.
• "E" or Enterprise train features and a command-set for specific equipment.
• "S" or Service Provider train contains features and a command-set for specific ISP equipments.

The absence of a train identifier denotes a Mainline release. Security updates are releases for the mainline train, but new functionality is never added to the feature set.
The latest version of the IOS (as of this writing) is 24.4(11)T. To view the IOS version of your Cisco device:
           Router#show version

NOTE:
To practice configuring routers and switches, please download and install any network simulation program. i would recommend Cisco Packet Tracer.