This post is by no means an exhaustive tutorial about cisco 3800 router and how to configure their numerous features. It is just a step-by-step guide for the most basic configuration needed to make the router operational. When you first power on a new Cisco Router, you have the option of using the “setup” utility which allows you to create a basic initial configuration. However, in this post I will show you how to do this basic setup with the Command Line Interface (CLI). Mastering the Cisco Router CLI is essential for more complex configuration tasks and it is the most important knowledge you should acquire if you want to become a Cisco network administrator.
The basic CLI modes that we will be referring below are as following:
Router> <– User EXEC Mode
Router# <– Privileged EXEC mode
Router(config)# <– Global Configuration Mode
Router(config-if)# <– Interface Configuration Mode
Router(config-line)# <– Line Configuration Mode
I assume that you already have some basic knowledge of CLI and how to navigate between different configuration modes (user mode, privileged exec mode etc), so let’s get started:
Step1: Configure Access Passwords
The first step is to secure your access to the router by configuring a global secret password and also passwords for Telnet or Console as needed.
Enter into Global Configuration mode from the Privileged EXEC mode:
Router# configure terminal <– Privileged EXEC mode
Router(config)# <– Global Configuration Mode
In Global Configuration Mode you configure parameters that affect the whole router device. Here we will configure the Enable Secret password that you will be using from now own to enter into Privileged EXEC Mode from User EXEC Mode.
Router(config)# enable secret“somestrongpassword”
From now on, when you log in from user EXEC mode you will be asked for a password.
It is suggested also to configure a password for the Telnet Lines (VTY lines) which will secure your access when connecting via Telnet over the network.
Router(config)# line vty 0 4
Router(config-line)# password “strongTelnetPass”
Router(config-line)# login
Step2: Configure a Router Hostname
To differentiate your Router from other devices in the network, you should configure a Hostname for your device.
Router(config)# hostname My-Router
My-Router(config)#
Notice that your cisco 3825 router prompt changes to the new hostname that you have just set.
Step3: Configure IP addresses for Router Interfaces
This is an essential step in order for your router to be able to forward packets in the network. The most basic parameter for a Router Interface is the IP address. From Global Configuration Mode you need to enter into Interface Configuration Mode:
My-Router(config)# interface serial 1/1
My-Router(config-if)# ip address 100.100.100.1 255.255.255.252
My-Router(config-if)# no shutdown
My-Router(config-if)# exit
My-Router(config)# interface fastethernet 0/1
My-Router(config-if)# ip address 192.168.10.1 255.255.255.0
My-Router(config-if)# no shutdown
My-Router(config-if)# exit
Step4: Configure Routing (Static or Dynamic)
The Router’s main purpose is to find the best route path towards a destination network and forward packets according to the best path. There are two main ways a router knows where to send packets. The administrator can assign static routes, or the router can learn routes by using a dynamic routing protocol. For simple network topologies, static routing is preferred over dynamic routing. Let’s see how to configure static cisco3825 router from Global Configuration Mode.
My-Router(config)# ip route [destination network] [subnet mask] [gateway]
My-Router(config)# ip route 200.200.200.0 255.255.255.0 100.100.100.2
The command above tells the router that network 200.200.200.0/24 is reachable via gateway address 100.100.100.2.
Another popular static route that we usually configure on Internet Border routers is the default static route:
My-Router(config)# ip route 0.0.0.0 0.0.0.0 50.50.50.1
The default static route above instructs the router to send ALL packets that the router does not have a more specific route entry to gateway address 50.50.50.1 (which might be the ISP gateway address).
Step5: Save your configuration
Save your current running configuration into NVRAM.CISCO2811-AC-IP This will overwrite the startup configuration.
My-Router(config)# exit
My-Router# copy running-config startup-config
You can display your current configuration to verify your settings as following:
My-Router# show running-config
