Day 16 Basic Router Configuration and Verification

CCNA 640-802 Exam Topics

  Access and utilize the router to set basic parameters (CLI/SDM).

  Connect, configure, and verify operation status of a device interface.

  Implement basic router security.

  Verify device configuration and network connectivity using ping, traceroute, telnet, SSH, or other utilities.

  Verify network connectivity (using ping, traceroute, and telnet or SSH).

Key Topic

Today we review the basic router configuration and verification commands as well as testing using the ping, traceroute, and telnet commands. Most of this should be very familiar to you at this point in your studies because these skills are fundamental to all other router configuration tasks.

Basic Router Configuration

Figure 16-1 shows the topology and addressing scheme we will use to review basic router configuration and verification tasks.

Figure 16-1      Basic Router Configuration Topology

When configuring a router, certain basic tasks are performed, including the following:

  Naming the router

  Setting passwords

  Configuring interfaces

  Configuring a banner

  Saving changes on a router

  Verifying basic configuration and router operations

Table 16-1 shows the basic router configuration command syntax used to configure R1 in the following example.

Table 16-1      Basic Router Configuration Command Syntax

Let’s walk through a basic configuration for R1. First, we enter privileged EXEC mode and then we enter global configuration mode:

Next, name the router and enter the encrypted password for entering privileged EXEC mode. This command overrides the older enable password password command so we are not entering that one:

Next, configure the console password and require it be entered with the login password:

Then configure the password for the Telnet lines and require it to be entered with the login password:

Configure the message-of-the-day (MOTD) banner. A delimiting character such as a # is used at the beginning and at the end of the message. At a minimum, a banner should warn against unauthorized access. A good security policy would prohibit configuring a banner that “welcomes” an unauthorized user:

Now configure the individual router interfaces with IP addresses and other information. First, enter interface configuration mode by specifying the interface type and number. Next, configure the IP address and subnet mask:

It is good practice to configure a description on each interface to help document the network information:

Activate the interface:

In a lab environment, we add a clock rate on the DCE side. However, in production environments the service provider sets the clock:

Assuming the other side of the link is activated on R2, the serial interface will now be up. Finish R1 by configuring the FastEthernet 0/0 interface:

Assume R2 is fully configured and can route back to the 192.168.1.0/24 LAN attached to R1. We need to add a static route to R1 to ensure connectivity to R2’s LAN. Static routing is reviewed in more detail on Day 14. For now, enter the following command:

To save the configuration, enter the copy running-config startup-config command or copy run start.

You can use the show running-config command to verify the full current configuration on the router; however, a few other basic commands can help you not only verify your configuration, but help you begin troubleshooting any potential problems.

First, make sure the networks for your interfaces are now in the routing table by using the show ip route command, as demonstrated in Example 16-1.

Example 16-1   The show ip route Command

If a network is missing, check your interface status with the show ip interface brief command, as demonstrated in Example 16-2.

Example 16-2   The show ip interface brief Command

The output from the show ip interface brief command provides you with three important pieces of information:

  IP address

  Line Status (column 5)

  Protocol Status (column 6)

The IP address should be correct, and the interface status should be “up” and “up”. Table 16-2 summarizes the two status codes and their meanings.

Table 16-2      Interface Status Codes

Four combinations of settings exist for the status codes when troubleshooting a network. Table 16-3 lists the four combinations, along with an explanation of the typical reasons why an interface would be in that state.

Table 16-3      Combinations of Interface Status Codes

If necessary, use the more verbose show interfaces command if you need to track down a problem with an interface. Example 16-3 shows the output for FastEthernet 0/0.

This command has a lot of output. However, sometimes this is the only way to find a problem. Therefore, Table 16-4 parses and explains each important part of the show interfaces output.

Table 16-4      show interfaces Output Explanation

Verifying Network Connectivity

As reviewed on Day 20, “Host Addressing, DHCP, and DNS,” ping and traceroute are helpful tools for verifying network connectivity. These tools work for routers as well. The only difference is the command output and the command syntax.

Example 16-4 demonstrates successful ping output on the router.

Example 16-4   Ping Output on a Router

Unsuccessful ping output shows periods (.) instead of exclamation points (!) as demonstrated in Example 16-5.

When tracing the route to the destination, use the command traceroute on a router instead of the tracert command used on a Windows PC. Example 16-6 shows output from a successful traceroute command.

Unsuccessful traces will show the last successful hop and the asterisks for each attempt until the user cancels. To cancel the traceroute command on a router, use the key combination Ctrl+Shift+6, and then the x key. Example 16-7 shows unsuccessful traceroute output.

Example 16-7   Unsuccessful Trace Route Output on a Router

Using Telnet or SSH to remotely access another device also tests connectivity. More importantly, these remote access methods will test whether a device has been correctly configured so that you can access it for management purposes. This can be very important when a device is truly remote (for example, across town or in another city). Day 8, “Switching Technologies and VLAN Concepts,” reviews SSH configuration and verification in greater detail.

During our basic configuration tasks earlier, we entered the commands to properly configure the Telnet lines (vty 0 4) for remote access. Example 16-8 shows a success Telnet from R1 to R2.

If R2 does not have a password configured, you might see the following output shown in Example 16-9.