9: Cisco IOS, The Router Device

9.1 LAN and WAN interfaces

Image1759.JPGFigure 9.1 LAN vs. WAN

Suppose that a company has two branches, one of them is in Cairo, and the other one is in New York.

The network that exists in Cairo branch is called a ‘LAN’ (Local Area Network).

The network that exists in New York branch is called a ‘LAN’ (Local Area Network).

The network that connects between the two branches through the internet is called a ‘WAN’ (Wide Area Network).

Therefore, we can deduce the following,

The LAN (local area network) is the network that exists in a limited boundary of a geographical area.

The WAN (wide area network) is the network that exists in a wide geographical area.

As you can see in the figure (9.1),

The LAN is always connected to the router through its ‘ethernet port’. Therefore, the ethernet port is the LAN interface.

The WAN is always connected to the router through its ‘serial port’. Therefore, the serial port is the WAN interface.

9.2 The router’s hardware

Every router contains hardware and software. In addition, there are many router models, every model has its certain capabilities and features and external body shape.

Every router’s model contains a certain number of ethernet ports and serial ports. However, some router models allow you to increase the number of ports by plugging some modules in them.

In figure (9.2), you can see a router that contains only two ethernet ports.

Image1767.JPG Figure 9.2:a router.

We can increase the number of the ethernet ports by plugging a module that contains extra number of ethernet ports in the router.

In figure (9.3), you can see the router’s module that contains the extra ethernet ports.

In figure (9.4), you can see the place that accepts the external router’s module.

Image1775.JPG Figure 9.3: a router‘s module.

Image1784.JPG Figure 9.4: a router that accepts an external module.

9.2.1 Configuring a router

5618.jpg Figure 9.5:some ports of the router.

In figure (9.5), you can see a router that contains a serial port, an ethernet port, a console port, and an auxiliary port.

To configure a router, we have three methods to connect to it,

Using a console port

Simply connect the computer to the console port using a rolled cable.

Using an auxiliary port

The auxiliary port enables us to connect to the router while we are a way from the company, this is done by connecting the auxiliary port to a modem, and if we need to connect to the router from outside the company, we dial up this modem, which connects us to the router.

Using the telnet

Using any telnet application in our computer enables us to telnet the router and configures it. (Of course, you must be the network admin to have the telnet username and password).

9.3 Booting up a router

9.3.1 Memory types on the router

Flash memory

It contains Cisco IOS (the operating system that operates the router).

NVRAM (non-volatile RAM)

It holds the ‘startup configuration’ and the ‘configuration register value’.

Startup configuration is the configuration configured on the router and then stored to the NVRAM.

Configuration register value is a value that determines the booting sequence of the router.

ROM

It contains the ‘POST’ and the ‘Bootstrap’.

POST (power on self-test) is a program that checks the router’s hardware when starting up.

Bootstrap is a program that loads the IOS when the router starts up.

RAM

It holds the ‘running configuration’.

The difference between the RAM and the other memory types is that when the power gets off, all the data that exists on the RAM will be deleted.

Running configuration is the actual configuration that the router uses.

9.3.2 The startup configuration vs. the running configuration

The startup configuration is the configuration that configured on the router and then stored to the NVRAM. So that the configuration will never be deleted when the router shuts down.

The actual configuration that the router uses while it is working, is the running configuration that exists on the RAM.

When the router starts up, it loads the startup configuration from the NVRAM to the RAM; this is done in order to make it the running configuration that the router should work from.

9.3.3 The router booting up sequence

  1. POST checks the router’s hardware.
  2. Bootstrap loads Cisco IOS from the flash memory.
  3. Cisco IOS looks for the startup configuration in the NVRAM.
  4. The startup configuration is copied to the RAM, which converts this configuration to be the running configuration that the router should use in its operation.