Configure Router

Unlike home routers, configuring business class routers need a good networking knowledge and at certain networking environment level, a strong knowledge about networking is needed to configure router properly.


Configuring home routers (such as Netgear WNDR3700 or WRT610N Linksys which are typically integrated with the firewall NAT feature, a 4 port LAN Switch, and a wireless access point) do not need a complexity knowledge in computer networking. But for business class routers, there are many tasks and configuration concepts to configure the router including modifying router configuration, enabling the interfaces, and so on.

Modifying router configuration

To view current router configuration files using commands such as show running-config, you need to be in the Privileged Exec mode. But if you need to configure router for actual changes you must be in a configuration mode. Different configuration tasks need separate configuration modes.

User exec-mode

Configure router in User exec-mode / User mode (> prompt) does not have any privilege, which allow you display information about the router, no configuration changes allowed.

• You can use console to interact with the router, which is direct connection to the router and enabled by default.
• You can administer the router remotely using telnet. With telnet you can establish a virtual terminal session over LAN connection. Initial configuration is needed such as enable the password and assigning the router IP address

Privilege EXEC mode

Privilege EXEC mode (# prompt) allows you view router configuration both running-config and startup-config files. The only changes you can configure router in Privilege EXEC mode are copying / overwriting the files configuration and restarting the router.

In the previous article discussed about router hardware including the startup-config file, running-config file. Startup-config file is saved in NVRAM and is used by the router when it boots up. Startup-config file might be different with the current running-config file. To save the current running-config file to the startup-config file, you have to do a copy using write memory command. Running-config file is saved in RAM and is used by the router in the current session. Any changes in configuration mode will take effect in the running-config file. But if the router is rebooted the router will use the startup-config file.

Global Configuration mode

Global Configuration mode allows you modify – configure router including any changes as a whole. For other configuration mode you can modify specific portions of the router configuration such as interfaces, subinterfaces, controller, line etc. Remember that in this configuration mode you can not view the router configuration.

Initialization Tasks

To configure router you should arrange the router to have a direct connection to the console before performing the basic configuration tasks.

1. Type in the config t command and the password to enter the global configuration mode.
2. To make any configuration changes, use the appropriate command
3. Type in exit or ^Z to exit the global configuration mode
4. Save the changes to overwrite the startup-config file by typing copy run start

Enabling the router password has been discussed in the other article, now we need to enable IP addresses.

Enabling IP interfaces

To allow the router to communicate you need to configure the router by assigning the LAN and the WAN interfaces. IP and IP routing are both enabled by default, but to allow a remote session via virtual terminal connection you need to assign the IP address. See also IP routing guide.

1. Type config t from the privilege EXEC mode to enter global configuration mode
2. Switch to the appropriate interface configuration mode
3. Use appropriate commands to make any changes
4. Exit to privilege mode and save the changes

Complete the following steps to assign the IP address for the interface:

Set the IP address 202.102.1.10 subnet mask 255.255.255.240 for example serial 0 interface (s0):

Router (config)#int s0

Router (config-if )#ip address 202.102.1.10 255.255.255.240

Router (config-if )#no shutdown

‘No shutdown’ command will enable the interface.

To verify the IP address, view the run-config using either:

• Show protocols
• Show interfaces
• Show ip interfaces

Configure router with the hostname is often helps when you have many routers as an identifications for each of the routers. The hostname will appear in the EXEC prompt.

Use this command:

Router (config)#hostname HRD (assigning the HRD hostname to the router) and the prompt will change to HRD (config)#

Viewing the interfaces status helps you in troubleshooting the network connection. The readiness of the interfaces to communicate with other devices can be indicated by the interface status.

• Line status which corresponds to the OSI physical layer indicates if the hardware link to the network is functional.
• Line protocol status / link status which correspond to the OSI Data link layer indicates if the necessary communication software is functioning properly.

Status	Description
Administratively down, line protocol is down, line protocol down	The interface is shutdown with the ‘shutdown’ command. It indicates hardware problem, no carrier detect signal
Up, line protocol is down	There is a communication problem, no keepalives – indicates a Data link layer problem
Up, line protocol is up	The link is functional

When you see the interface status is “up, line protocol is up” one more additional task to assure the communication between routers take place, you need to assign the IP address to allow the upper layers from Network layer through Application layers function.

Setup Mode

For a brand new router, you will be prompted with the setup mode when the router boots up. With setup mode, the router will guide you through the routine process with series of questions; and your responses will be used as basic configuration entries. It’s an initial router configuration.


You can enter the setup mode in two ways:

• Type in the ‘setup’ command from the privilege mode
• When you boot the router with no startup-config file due to the current startup-config file is erased. Or booting a brand new router. you can use the ‘erase nvram’ command to delete the startup-config file.

With the basic setup mode, you can

• Set the router hostname
• Set the enable and enable secret passwords as well as virtual terminal passwords
• Enable and assigning the IP address to the interfaces

While in the extended setup mode you can configure router to:

• Configure more than one interface
• Configure additional protocols and also the routing protocols

See also related articles:

• wireless firewall NETGEAR’s SRXN3205 ProSafe® Wireless-N VPN Firewall and external firewall standards.
• WAN services technology
• Understanding Cisco IOS
• VPN network connection
• Cisco RV082 Router redundancy