Configure Initial Router Settings
Basic Router Configuration Steps
The following tasks should be completed when configuring initial settings on a router.
1. Configure the device name.
Router(config)# hostname
2. Secure privileged EXEC mode.
Router(config)# enable secret password
3. Secure user EXEC mode.
Router(config)# line console 0
Router(config-line)# password password
Router(config-line)# login
4. Secure remote Telnet / SSH access.
Router(config-line)# line vty 0 4
Router(config-line)# password password
Router(config-line)# login
Router(config-line)# transport input {ssh | telnet}
5. Secure all passwords in the config file.
Router(config-line)# exit
Router(config)# service password-encryption
6. Provide legal notification.
Router(config)# banner motd delimiter message delimiter
7. Save the configuration.
Router(config)# end
Router# copy running-config startup-config
Basic Router Configuration Example
In this example, router R1 in the topology diagram will be configured with initial settings.
To configure the device name for R1, use the following commands.
Note: Notice how the router prompt now displays the router hostname.
All router access should be secured. Privileged EXEC mode provides the user with complete access to the device and its configuration. Therefore, it is the most important mode to secure.
The following commands secure privileged EXEC mode and user EXEC mode, enable Telnet and SSH remote access, and encrypt all plaintext (i.e., user EXEC and VTY line) passwords.
The legal notification warns users that the device should only be accessed by permitted users. Legal notification is configured as follows.
If the previous commands were configured and the router accidently lost power, all configured commands would be lost. For this reason, it is important to save the configuration when changes are implemented. The following command saves the configuration to NVRAM.
Configure Interfaces
Configure Router Interfaces
At this point, your routers have their basic configurations. The next step is to configure their interfaces. This is because routers are not reachable by end devices until the interfaces are configured. There are many different types of interfaces available on Cisco routers. For example, the Cisco ISR 4321 router is equipped with two Gigabit Ethernet interfaces:
- GigabitEthernet 0/0/0 (G0/0/0)
- GigabitEthernet 0/0/1 (G0/0/1)
The task to configure a router interface is very similar to a management SVI on a switch. Specifically, it includes issuing the following commands:
Note: When a router interface is enabled, information messages should be displayed confirming the enabled link.
Although the description command is not required to enable an interface, it is good practice to use it. It can be helpful in troubleshooting on production networks by providing information about the type of network connected. For example, if the interface connects to an ISP or service carrier, the description command would be helpful to enter the third-party connection and contact information.
Note: The description-text is limited to 240 characters.
Using the no shutdown command activates the interface and is similar to powering on the interface. The interface must also be connected to another device, such as a switch or a router, for the physical layer to be active.
Note: On inter-router connections where there is no Ethernet switch, both interconnecting interfaces must be configured and enabled.
Configure Router Interfaces Example
In this example, the directly connected interfaces of R1 in the topology diagram will be enabled.
To configure the the interfaces on R1, use the following commands.
Note: Notice the informational messages informing us that G0/0/0 and G0/0/1 are enabled.
Verify Interface Configuration
There are several commands that can be used to verify interface configuration. The most useful of these is the show ip interface brief and show ipv6 interface brief commands, as shown in the example.
Configuration Verification Commands
The table summarizes the more popular show commands used to verify interface configuration.
Configure the Default Gateway
Default Gateway on a Host
If your local network has only one router, it will be the gateway router and all hosts and switches on your network must be configured with this information. If your local network has multiple routers, you must select one of them to be the default gateway router. This topic explains how to configure the default gateway on hosts and switches.
For an end device to communicate over the network, it must be configured with the correct IP address information, including the default gateway address. The default gateway is only used when the host wants to send a packet to a device on another network. The default gateway address is generally the router interface address attached to the local network of the host. The IP address of the host device and the router interface address must be in the same network.
For example, assume an IPv4 network topology consisting of a router interconnecting two separate LANs. G0/0/0 is connected to network 192.168.10.0, while G0/0/1 is connected to network 192.168.11.0. Each host device is configured with the appropriate default gateway address.
In this example, if PC1 sends a packet to PC2, then the default gateway is not used. Instead, PC1 addresses the packet with the IPv4 address of PC2 and forwards the packet directly to PC2 through the switch.
The diagram is a network topology with one router, two switches, and four PCs showing the flow of information between devices on the same network. PC1 and PC2 are connected to the switch on network 192.168.10.0/24 at interface G0/0/0 on router R1. PC3 and PC4 are connected to another switch on network 192.168.11.0/24 at interface G0/0/1 on R1. An arrow shows the flow of information sent from PC1 passing through the attached switch on its way to PC2.
What if PC1 sent a packet to PC3? PC1 would address the packet with the IPv4 address of PC3, but would forward the packet to its default gateway, which is the G0/0/0 interface of R1. The router accepts the packet and accesses its routing table to determine that G0/0/1 is the appropriate exit interface based on the destination address. R1 then forwards the packet out of the appropriate interface to reach PC3.
The same process would occur on an IPv6 network, although this is not shown in the topology. Devices would use the IPv6 address of the local router as their default gateway.
Default Gateway on a Switch
A switch that interconnects client computers is typically a Layer 2 device. As such, a Layer 2 switch does not require an IP address to function properly. However, an IP configuration can be configured on a switch to give an administrator remote access to the switch.
To connect to and manage a switch over a local IP network, it must have a switch virtual interface (SVI) configured. The SVI is configured with an IPv4 address and subnet mask on the local LAN. The switch must also have a default gateway address configured to remotely manage the switch from another network.
The default gateway address is typically configured on all devices that will communicate beyond their local network.
To configure an IPv4 default gateway on a switch, use the ip default-gateway ip-address global configuration command. The ip-address that is configured is the IPv4 address of the local router interface connected to the switch.
The figure shows an administrator establishing a remote connection to switch S1 on another network.
In this example, the administrator host would use its default gateway to send the packet to the G0/0/1 interface of R1. R1 would forward the packet to S1 out of its G0/0/0 interface. Because the packet source IPv4 address came from another network, S1 would require a default gateway to forward the packet to the G0/0/0 interface of R1. Therefore, S1 must be configured with a default gateway to be able to reply and establish an SSH connection with the administrative host.
Note: Packets originating from host computers connected to the switch must already have the default gateway address configured on their host computer operating systems.
A workgroup switch can also be configured with an IPv6 address on an SVI. However, the switch does not require the IPv6 address of the default gateway to be configured manually. The switch will automatically receive its default gateway from the ICMPv6 Router Advertisement message from the router.
What did I learn in this module?
Configure Initial Router Settings
The following tasks should be completed when configuring initial settings on a router.
- Configure the device name.
- Secure privileged EXEC mode.
- Secure user EXEC mode.
- Secure remote Telnet / SSH access.
- Secure all passwords in the config file.
- Provide legal notification.
- Save the configuration.
Configure Interfaces
For routers to be reachable, the router interfaces must be configured. The Cisco ISR 4321 router is equipped with two Gigabit Ethernet interfaces: GigabitEthernet 0/0/0 (G0/0/0) and GigabitEthernet 0/0/1 (G0/0/1). The tasks to configure a router interface are very similar to a management SVI on a switch. Using the no shutdown command activates the interface. The interface must also be connected to another device, such as a switch or a router, for the physical layer to be active. There are several commands that can be used to verify interface configuration including the show ip interface brief and show ipv6 interface brief, the show ip route and show ipv6 route, as well as show interfaces, show ip interface and show ipv6 interface.
Configure the Default Gateway
For an end device to communicate over the network, it must be configured with the correct IP address information, including the default gateway address. The default gateway address is generally the router interface address for the router that is attached to the local network of the host. The IP address of the host device and the router interface address must be in the same network. To connect to and manage a switch over a local IP network, it must have a switch virtual interface (SVI) configured. The SVI is configured with an IPv4 address and subnet mask on the local LAN. The switch must also have a default gateway address configured to remotely manage the switch from another network. To configure an IPv4 default gateway on a switch, use the ip default-gateway ip-address global configuration command. Use the IPv4 address of the local router interface that is connected to the switch.
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